Nothing Is Where You Left It
Nine stories, each built on a mechanism that works.
The author has loved real science fiction all his life and has never had much patience for the other kind, where the hardware is a rumour and the physics is whatever the plot needs this week. In every story here the thing driving the plot is a real effect taken from the working literature, and the people are up against it on its own terms: a cold mirror that catches water out of nothing, a memory array that quietly certifies its own mistakes, a rock whose equator throws things off it, an atmosphere that freezes onto the floor as a planet moves away from the Sun. Nothing is solved by a device that has not been invented. Nobody gets a convenient discovery. The arithmetic is done out loud, and the places — the lunar south pole, the cloud deck of Venus, the waist of a spinning asteroid, Titan, where a person with wings can genuinely fly — are described as they are known to be.
Each story is followed at the back of the book by a short note naming the mechanism it turns on and stating plainly how much of it is established physics, how much is standard engineering practice, and how much is extrapolation. None of it is needed in order to read the stories. It is there so that a reader who wants to check the author’s work can do it without leaving the volume.
Contents
Nothing Is Where You Left It 53
Notes on Scientific Plausibility. 234
Nothing Is Where You Left It 238
The Sharpness Budget
The first thing that went wrong went wrong beautifully, which is how Ileana Brăiloiu knew it would take a month to explain and a year to forgive.
At 03:14 vehicle time the calibration frame came up from Threnody’s focal plane, and every star in it was wearing a halo. Not a smear, not a streak, nothing an engineer could point at and call a failure. Each point source sat exactly where the ephemeris promised, perfectly centred, perfectly round, and perfectly collared in soft light, as though someone had breathed on the sky and then wiped it with a sleeve out of politeness.
— That’s gorgeous, said Kwabena Osei-Darko, arriving behind her with a bulb of coffee he was not supposed to have in the instrument bay. Put it on a stamp.
— It’s a point-spread function with wings.
— Ghana issues a stamp, Romania issues a stamp, we are both immortal and slightly rich.
The wings were the problem and Kwabena knew it before she said it, which was why he was making jokes; it was his version of putting a hand on someone’s shoulder, and on this vehicle putting a hand on someone’s shoulder had become a loaded manoeuvre for reasons nobody was discussing. A telescope’s point-spread function is its signature, the shape a single star makes when the optics behave. The core carries the signal. The wings are what spills out around the core, and when the wings rise, every faint thing drowns in the glare of every bright thing near it. Threnody existed to look at objects ten billion times fainter than the star they orbit, sitting a fraction of an arcsecond away. A halo of this size, measured honestly, meant the starlight suppression had degraded by something near a factor of forty. It meant the most important instrument ever flown had stopped being able to do the one thing it was for.
Ileana pulled the previous three nights. The wings were in all of them, smaller, smaller, smallest, a curve rising so smoothly that nobody had flagged it, because each night’s number sat comfortably inside the night before’s error bar. That is how real degradations arrive. Catastrophes announce themselves. Slow ruin files paperwork.
— Since when, said Kwabena, no longer performing.
— Since we got here, said Ileana, and heard her own voice go flat, because she had already done the arithmetic and did not like where it landed.
⁂
They had arrived nineteen days earlier, after five months of cruise, in a servicing vehicle named Aubade that had cost roughly what a middling country spends on bridges and had been approved in a single afternoon by a legislature that normally could not agree on the price of coffee. That unanimity had a cause, and the cause had a name, and the name was in every schoolroom on Earth.
For thirty years exoplanet science had been counting. Kepler counted magnificently — thousands of worlds, a statistical census of the galaxy’s habits — but counting is done by watching a star dim as something crosses it, and a dip in a light curve gives you a diameter and a period and almost nothing else. The planets that came back in any detail were the loud ones: hot Jupiters, bloated Neptunes, the endless middle class of super-Earths and sub-Neptunes the galaxy turns out the way a bakery turns out rolls. Everyone knew the small cool rocky worlds were there. Nobody could see one. The threshold sat for three decades like a locked door with light under it.
Threnody took the door off its hinges. Not by being large — it was not especially large — but by being cold, and quiet, and carrying a coronagraph whose job was to delete a star and leave what surrounds it visible. At thirty-nine kelvin, working in the mid-infrared where a temperate planet actually glows rather than merely reflects, with a wavefront loop holding the optics still to a few tens of picometres, it did in its first year what the whole previous history of the field had failed to do. It imaged a rocky planet in a habitable zone. Then it took its spectrum.
Then it did it again, and then the discoveries came down in bunches.
Proxima b first, inevitably, a world people had argued about for a decade on the strength of a wobble. Threnody resolved it, found it tidally locked and weathered, measured carbon dioxide and water and a hydrogen feature that started three separate feuds. Barnard’s Star next, where the little family of sub-Earths turned out to have one more member, further out and colder, surfaced in water ice nobody had predicted. Then the real haul. Tau Ceti e, twenty years a contested squiggle in a radial-velocity dataset, came up as a disc of light with an atmosphere thick enough to fight about, and the fight was ongoing and vicious and wonderful. GJ 1002 c showed water vapour and a thermal map with a cold pole. Teegarden’s Star b showed oxygen and methane in the same spectrum — the combination that is not supposed to persist unless something keeps replenishing it — and the cautious phrasing in the discovery paper, a persistent chemical disequilibrium of unestablished origin, was the most exciting sentence written in any language that year. Lalande 21185. Ross 128. GJ 887. Luyten’s star. YZ Ceti. Fourteen temperate rocky worlds characterised in six years, after thirty years of none.
That was why three people were sent a million and a half kilometres from Earth with a detector in a padded case. The focal-plane array Threnody had launched with was superb and was by now the slowest part of a machine that had found fourteen Earths. The replacement would cut the integration time for a full spectrum by a factor of six. Six times more worlds per year. The budget passed in an afternoon because by then the public had learned the names of other planets and had opinions about them, and in one documented case had named a cat after Teegarden b.
The obvious question had been asked, loudly, for two years, by people who were entirely right to ask it: why send bodies? A robot does not sweat. Everyone understood that before anybody was selected; it was the first line of every objection and the last line of every cartoon.
The answer was that Threnody had been built in an era that had quietly given up on servicing. Its focal plane sits behind a shroud secured by forty captive fasteners whose torque history is a matter of belief, cold-soaked for six years at thirty-nine kelvin, with dissimilar metals in contact and a non-trivial chance that some of them have grown into each other. There are no grapple fixtures, no blind-mate connectors, no servicing interface of any kind, because adding one would have cost mass and because the programme that paid for the observatory was a telescope programme and not a logistics programme. Two robotic concepts had been funded through preliminary design. Both ran into the same wall and the wall was not dexterity, it was time delay. L2 is five seconds of light round trip, and a teleoperated arm under five seconds of delay does not work in a continuous loop; it works in move-and-wait, a command, a pause, a look, another command, which multiplies task duration by something between twenty and fifty. A procedure a crew completes in thirteen hours becomes a robotic campaign of months, every hour of it one hardware fault away from a fastener backed halfway out of a blind hole with a cryogenic connector half demated and nobody within a million and a half kilometres able to reach in and sort it out. Full autonomy was the other branch, and an autonomous system able to improvise around a seized fastener in a one-off geometry it has never touched is not a servicing robot, it is a decade of development and more money than the crewed option, delivered later, at the cost of the very years the new detector was supposed to buy back.
So the trade was stated honestly in the decision memorandum, in a sentence that was later quoted in three parliaments: a clean machine that will probably fail, or dirty animals who will certainly succeed and will certainly make a mess.
Ileana had been on the imaging team that produced the Proxima spectrum. Yusuf Tanrıkulu had built the wavefront sensor that made it possible. They had met across an alignment dispute four years ago, had conducted that dispute at a volume that cleared a corridor, had been correct in different directions, and had then spent four years being assigned to the same reviews by a management that mistook their arguments for friction rather than for whatever they actually were.
⁂
Yusuf came up through the hatch with his hair doing what hair does in free fall, looked at the frames, looked at the curve, and said the sentence that made it official.
— It’s us.
— We don’t know that.
— We are the only new thing within a million kilometres. Either the universe went soft precisely when we showed up, or we brought the softness with us. I have met the universe. It is not that interested in our schedule.
He came down the rail to the console and stopped at the distance he always stopped at now, which was about forty centimetres further than he used to stop and had been recalculated, Ileana was certain, as deliberately as any trajectory on board. She had done her own recalculation. Theirs did not match, and the mismatch was the most carefully maintained piece of engineering on the vehicle.
— Nineteen days, he said quietly. Twenty-two excursions.
— Twenty-two, said Ileana.
The baseline had been eighteen.
⁂
Here is what Ileana had done, and it is worth being exact, because she was exact about it afterwards for the rest of her life.
The plan allotted eighteen excursions across twenty-six days. On day two she looked at the real rate of work — they were good, the hardware fit, the fixtures behaved — and saw that by adding two excursions a week and compressing the rest periods she could finish nine days early. Nine days mattered. Nine days meant Threnody back on sky in time for the November quadrature of 82 Eridani, a sun-like star twenty light years out, around which the observatory had found a planet of one and a quarter Earth masses on a four-hundred-and-ninety-day orbit with a thermal signature that two independent groups had modelled as an ocean.
The geometry of that target was cruel. To image a planet you need it well off its star on the sky, near maximum elongation, and Threnody’s field of regard excludes a broad band around the Sun that sweeps the sky once a year. The planet’s year and the observatory’s year beat against each other, and the two constraints agree for a usable stretch about every nine years. The next window opened in November. The one after that opened when Ileana would be fifty.
So she compressed the schedule, and the crew agreed, enthusiastically, because they wanted it too and because she was good at explaining why a hard thing was worth doing. Four extra excursions. Twenty-six additional hours outside. And there was a second reason, which she did not put in the plan, and which was that an eighteen-hour working day leaves no evenings, and that evenings on a small vehicle with a man you have agreed in writing not to touch are the longest unit of time known to physics.
⁂
So how does the water get from a man’s back to a mirror behind a sunshade the size of a tennis court? It is worth following, because the answer is the whole story.
A spacesuit sheds metabolic heat through a sublimator: water is bled into vacuum through a porous plate, where it flashes to vapour and ice and carries the heat away. Hard work costs something near half a kilogram of water an hour. The discharge goes aft at several hundred metres a second, and in a straight line it never comes near the optics, which is what the original analysis said and what the original analysis was right about.
Nothing travels in a straight line for long near a spacecraft. Within a few centimetres of the plate the plume is dense enough to collide with itself, and self-collisions throw a tail of molecules out at wide angles. Those wide-angle molecules strike the vehicle’s own structure — and Aubade carried, courtesy of a mass-saving change approved three years after the plume analysis, a flat multilayer insulation apron at a sympathetic angle. Warm surfaces do not retain water. They re-emit it thermally, in a broad cosine distribution, which is to say in every direction including forward, past the edge of the shade, into the cavity. From there the molecule flies ballistically until it hits something, and the coldest something for a million kilometres in every direction is a mirror at thirty-nine kelvin.
At that temperature water does not bounce. It arrives, it sticks with a probability very close to one, and nothing evaporates back off. The layer only grows.
The brutal part is the bookkeeping. A hundred nanometres of amorphous ice is about ten micrograms per square centimetre; across the aperture, call it a gram. Twenty-two excursions had put something near seventy kilograms of water overboard. The return fraction required to ruin the most expensive instrument in history was therefore about one molecule in fifty thousand. No engineer on Earth designs against a leak of one part in fifty thousand. No cold mirror in the universe forgives one.
The fabric that steals the sharpness of outlines. Ileana wrote that in the margin of the fault log at 04:40, deleted it, and put it back two minutes later.
⁂
Ground took forty-nine minutes round trip, which gave every exchange the texture of arguing by post with someone always slightly in the past and entirely certain. The first reply came from Dr. Henrietta Volk, contamination control, who had spent twelve years of her working life — she said this the way a woman quotes a sentence handed down by a court — keeping Threnody’s optics cleaner than the air of any operating theatre on Earth.
— Good morning, Aubade. I have reviewed the frames. Before anyone uses the word contamination on an open loop I remind the crew that the particulate ledger is nominal. Deposition has tracked the model within twelve percent since your arrival. The ledger does not lie.
— The ledger does not lie, said Kwabena, delighted. The ledger merely declines to comment.
— I heard that in advance, said Volk, forty-nine minutes later, which was the funniest thing she had ever done and almost certainly unintentional.
The ledger was a serious instrument measuring the wrong quantity. It tracked mass released. What mattered was where the mass went, in what form, and whether it found anything cold.
— So we built a snow cannon, said Kwabena, reading the apron geometry, and aimed it at the finest mirror our species has.
— We built a snow cannon, said Yusuf, and then the agency bolted a backboard onto it.
— The second gauge is worse, said Kwabena, who had pulled the microbial swabs because Volk’s office counts organisms as devotedly as it counts grams. Water isn’t all we’re shedding. A working human sheds skin at a rate I am not going to read aloud before dinner, and a measurable fraction of what comes off a person is alive, or was recently, or is waiting to find out. Which makes that ice layer, technically, a thin film of distilled water at thirty-nine kelvin seeded with the most travelled microbiome in history.
— It’s not a habitat, said Yusuf. It’s a freezer with a view.
— It is a freezer with a view and a guest list, said Kwabena. And observe that we came out here to look for life, and the first thing we did on arrival was put some on the lens.
— Nothing is going to grow on a mirror at thirty-nine kelvin.
— Nothing is going to grow, Kwabena agreed. That is the only reason it’s funny. The nearest place anything of ours could grow is twenty light years off, which is, on reflection, a well-judged distance. Our species has a long history of arriving somewhere clean and improving it, and the one mercy of this profession is that the interesting real estate is too far away for us to sneeze on.
— Please put that in the report exactly like that, said Ileana.
— I will write no credible proliferation pathway exists at the deposition site, said Kwabena, and the sentence will do forty years of work and nobody will ever read it.
Ileana said nothing, because the apron angle had not scheduled four extra excursions. She had, and she knew exactly why, and one of the two reasons was not in any document.
⁂
— Two branches, she said next morning, with a grease pencil on the bay’s scratched polycarbonate, while Kwabena filmed, because he filmed everything that might later be described as leadership. Both testable. Let’s stop having opinions.
— Branch one, the halo is in the sky. Zodiacal dust, a thermal gradient in the far field, anything out there. Then it is fixed with respect to the stars and does not care what attitude we hold.
— Branch two, said Yusuf, it is on us. Ice on the mirror or a cloud in our own near field, co-moving with the vehicle.
— And the discriminator is free. We roll.
A sensible reader will ask why nobody simply looked at the mirror. Because a contamination layer capable of killing a coronagraph is about a hundred nanometres thick. Shine a lamp on it and you see a mirror. The only instrument within a million kilometres sensitive enough to detect the problem was the instrument suffering from it, an irony that occurs in engineering far more often than anyone admits in public.
So they rolled. Threnody held pointing on a calibration star and rotated about the line of sight, sixty degrees at a time, taking a frame at each station. Sky-fixed structure spins in the data as the detector turns beneath it. Vehicle-fixed structure does not move at all.
The halo did not move. Six orientations, and it sat where it had sat the first time, locked to the telescope’s own axes: a circle of soft emptiness that belonged to them, travelled with them, and had been manufactured on site by three people breathing, sweating, venting and doing excellent work.
— We brought our own weather, said Kwabena.
Volk’s answer, when it came, had the brevity of real distress.
— Understood. The ledger was measuring the wrong thing. Stand by.
⁂
Crew Policy 9.2 is not a joke, although it is written in the prose of a man who has never been more than four metres from another human being for five consecutive months. It prohibits romantic or sexual relationships between crew members for the duration of an assignment, on the entirely sound grounds that a three-person vehicle has no spare social structure, that a falling-out at L2 cannot be resolved by anybody going home, and that a commander who is in love with a subordinate is an instrument with an uncalibrated offset.
Ileana had signed it, had believed in it on Earth, continued to believe in it in principle, and had spent four months discovering that principle is a word people use for things they have not yet had to carry.
The practical situation was, to be fair, hilarious, and Kwabena made certain that nobody was allowed to forget this.
— I just want to establish, he said, around month three, over a dinner of rehydrated beans, that the two of you have selected the single worst environment in the observable universe for this.
— For what, said Yusuf.
— For whatever it is you are both not doing. Which, by the way, you are not doing extremely loudly. Let me walk you through the engineering, since you’re engineers. Free fall. Newton’s third law. You push, she goes. She pushes, you go. Anything requiring sustained contact requires a restraint system, and our restraint systems were designed by a committee that has never once imagined this application and whose straps leave marks that the flight surgeon photographs. Thermal: no convection. Body heat does not rise, it sits on you in a shell, and in ten minutes you are both inside a small personal swamp. Fluid behaviour: nothing runs off. Nothing goes anywhere. It accumulates in a film and then detaches as a sphere and then floats into the air return and then, Ileana, my friend, my commander, it becomes a line item on the ledger.
— Please stop.
— I am being scientific. Volume: this vehicle has a habitable space the size of a generous bathroom and three humans in it, one of whom is me, and I do not sleep well. Acoustics: none. The partitions are a curtain and an optimistic assumption. And finally, logistics, which is the part everyone forgets: there is no shower. There is a wet wipe. There are eight hundred and forty wet wipes, manifested, counted, and inventoried by Dr. Volk’s office.
— She counts the wipes?
— She counts everything that holds water, said Kwabena. It is her whole professional identity. Imagine explaining the variance.
Yusuf, who had gone the colour of a man doing structural calculations about his own face, said:
— The literature does suggest that the realistic envelope is limited to, essentially, holding on to each other.
— The literature, said Kwabena, has clearly been written by people who tried.
And the appalling thing, Ileana thought — the thing that made the whole business so much worse rather than better — was that the limited envelope was not a consolation prize. In free fall two people holding on to each other are genuinely weightless together, which no couple on Earth has ever been; nothing presses, nothing tires, no arm goes numb, no one must support anyone. You simply stay, as long as you both decide to keep deciding. It is, by any honest accounting, the most romantic physical arrangement available to the species, and it had been placed four metres away from her for five months, behind a curtain, under a policy she had signed, in a vehicle where the fundamental operating hazard was the water that comes off a human body.
She had thought about that symmetry more than was good for her. Everything about this mission was the same problem. Warm wet animals, trying to hold still near something exquisite and cold that they could ruin by breathing on it.
⁂
That evening she found Yusuf in the galley with two bulbs of tea, one of which he handed over without being asked, which was how he conducted most arguments.
— Say it, he said.
— I added four excursions.
— We added four. I voted.
— You voted because I presented it well, and I presented it well because I wanted two things, and only one of them is in the plan.
He did not say anything for a while, which was his tact.
— I wanted November, she said. I have wanted that planet since the second detection paper. I compressed a contamination-critical timeline for nine days of sky, and I also compressed it because eighteen hours of work a day means we are never both awake and off shift, and I have been managing that like a thermal load since the second week of cruise. And now there is a hundred nanometres of me on that mirror, and I cannot tell any more which part of the schedule was the ocean and which part was the curtain.
— Does it matter which?
— It matters enormously. One of them is a defensible engineering judgement made with the information available. The other one is a woman using a billion-dollar observatory as a chaperone.
— It can be both, he said. Most things are both. That’s not a character flaw, that’s just how people with one body do two things at once.
— Don’t be kind to me, I’m trying to be accurate.
— You’re trying to be punished, said Yusuf. Those get confused in you. They always have. I noticed it in the alignment review four years ago and I have been noticing it steadily since, in considerable detail, with a frequency that I would describe to any ethics panel as professional.
— Yusuf.
— And I have forty-three days left on this policy, he said, — on which I am going to go to bed now, in the other direction, as I have done a hundred and forty times, with enormous discipline, which I am told builds character.
From behind the galley partition, where he had been floating silently for an unknown duration with an unauthorised coffee, Kwabena said:
— For the record, I’m the only unattached person aboard and therefore the only objective witness, and objectively that was the most restrained thing I have ever heard and I would like it read at my own wedding.
⁂
The decision was genuine, which is to say there was no clean answer.
Finish: four days to complete the installation, thirteen more hours of sublimator time, a contamination layer the models put at double its present thickness. Threnody would receive an instrument of extraordinary sensitivity and be unable to use it, the way a man given a violin in a room full of bees is technically a violinist.
Stop: undock now, go home with the detector in its case, leave the observatory with the halo it already has. Five months out, five months back, a bridge’s worth of money, and a headline Ileana could already see in a font she disliked.
The third option arrived on the second day, found by Yusuf the way third options are usually found, by refusing the shape of the question.
— The ice isn’t welded on. It’s physisorbed water on a cold surface. It’s parked. Warm the mirror and it leaves.
Decontamination bake-out is not exotic. Cryogenic instruments on the ground do it routinely and flight instruments have done it in orbit. Water desorbs along a brutally steep exponential in temperature: take the primary from thirty-nine kelvin to something near two hundred, hold it, and the layer sublimates away into space and takes the halo with it.
The costs came in two kinds, and the crew spent a day and a half discovering that they disagreed about which kind frightened them.
The first was arithmetic. Warming the mirror meant shutting the cryocooler chain and spending the stored cryogen margin, the mission’s insurance for its final years. Cooling back and settling to a stable figure would take six to eight weeks of nothing, and the margin spent would shorten the observatory’s operating life by close to a year — a year at the end, when the instrument is best understood and the target list richest. And no November. 82 Eridani in nine years, by whoever was holding the console then.
The second cost was not arithmetic. Threnody’s primary is a segmented beryllium structure with a gold coating a few hundred atoms thick, built on Earth at room temperature, cold-soaked for six years, never since warmed. Beryllium, gold, the adhesion layer between them and the composite backing all expand at different rates. Taking the assembly up by a hundred and sixty kelvin and back down meant running the whole thermal cycle in the wrong direction, once, with no spare.
— The coating could craze, said Yusuf. An actuator could seize at an intermediate temperature. We could get differential strain at a segment mount and put a permanent figure error into a mirror nobody can replace.
— Probability.
— Low. Not quotable. Nobody has ever done this to this mirror.
— So either the thermal model holds and we get the sharpness back for the price of a year, said Ileana, or it doesn’t hold, and we discover that we didn’t lose a year, we lost the telescope.
— That’s the fork, said Yusuf. I can’t close it from here and neither can Pasadena. The only instrument that could measure the answer is the one we’d be risking.
⁂
Volk’s reply did not sound like a committee.
— Aubade, the recommendation is bake-out and it is unanimous, and the sentence that ended the discussion came from the flight surgeon. She said: an instrument that can see is worth fewer years than an instrument that cannot. Dr. Brăiloiu, you have been careful not to say I told you so on an open loop, and I notice, and I have spent today thinking about the difference between a number that is correct and a number that is relevant, and I intend to publish on it at length under a title that will embarrass me. Dr. Osei-Darko, the stamp is apparently going to happen. The postal service has been in touch. Your face is involved.
— My face, said Kwabena, has always been involved.
⁂
They finished the detector first, since whatever they laid down now would come off with the rest.
The final excursion ran thirteen hours and it was not clean work. Inside a suit the body is a badly ventilated animal in a bottle: sweat does not run off, it pools and migrates and finds the inside of an elbow; the air carries a flat metallic smell everyone calls ozone and nobody has confirmed; somewhere around hour seven the pulse becomes audible behind the ears and stays, a slow soft thudding under the fan. Ileana worked with her hands inside gloves pressurised hard enough that closing a fist thirty times is a day’s exercise, and she closed a fist several hundred times, torquing captive fasteners on a housing machined to tolerances her own breath would have violated. Below her the shade lay white and flat. Four centimetres from her face, the visor; beyond it nothing at all, in every direction, forever, at three kelvin.
At hour ten, with the clarity that arrives once the body stops negotiating, she thought: the cleanest machine ever built, and the only thing within a million kilometres that cares whether it works is this warm wet sack of salt water, sweating on it. That is the permanent arrangement and there is no version of the job without it. Everything we have ever made that is finer than we are has had to be assembled, carried, repaired and eventually ruined a little by hands that leak. We are smudgers. We fog what we lean close to, we leave a fingerprint on every lens we have ever ground, and we go on leaning close anyway, because nothing else out here is interested.
— Status, said Yusuf on the loop, which meant something else.
— Hands are fine, said Ileana, which also meant something else.
The detector seated on the first attempt. Kwabena said something unrepeatable in Twi. Every channel came up alive.
⁂
They backed off to forty kilometres, which took the sublimators out of the geometry, sent the command, and Threnody began to warm at four kelvin an hour, slow enough to be boring and fast enough to break something.
The desorption gauge — a small sensor nobody had expected to become the most-watched instrument of the mission — showed water partial pressure climbing as the mirror passed a hundred and forty kelvin, peaking in a broad hump, falling to nothing. Nineteen days of ice left the surface one molecule at a time and dispersed into a volume where it would never meet anything cold again. What must die crumbles into a sweet snow, and then the snow is gone, because out here there is nowhere for snow to lie.
The trouble came on the way back down.
At ninety-four kelvin, descending, segment B4 stopped tracking its neighbours. The metrology showed its piston drifting, holding, drifting again, in steps of a few nanometres: the signature of a mechanism binding and releasing against thermal strain rather than moving under command. Yusuf watched it for forty minutes without speaking, which Ileana had seen him do exactly twice before.
— Either the actuator is binding and will free itself as the gradient relaxes, he said at last, or the mount is yielding, in which case it keeps walking, leaves capture range, and cannot be commanded back. Then the primary has a hole in it.
— How long until we know?
— That’s the problem. If it frees itself, it does so within two days. If it’s yielding, it also looks exactly like this for two days.
— And if it’s yielding and we wait?
— Then in two days the answer is permanent and we are forty kilometres away with our hands in our pockets.
Going back meant re-docking, which meant thrusters, which meant contaminating a mirror they had just cleaned at the price of a year. It also meant an excursion against a structure at ninety kelvin with a consumables budget written for a different mission.
Kwabena, who had been quiet, said:
— Third thing.
— There’s always a third thing. Go.
— If it’s binding, what frees it is a change of gradient, and we can change the gradient from here. Slew ninety degrees and let the shade shadow that structure differently for six hours. Friction unsticks with geometry. And it separates the branches in hours instead of days, because a yielding mount responds to a load change and a seized actuator doesn’t.
Yusuf looked at him with an expression that Ileana, watching, catalogued and kept.
— That’s the discriminator, he said. Free and fast.
They slewed. Two hours of nothing. In the third hour B4 released in a single clean step of seven nanometres and settled, and the metrology went quiet and stayed quiet, and Ileana discovered that she had been gripping a handrail hard enough to leave marks in her palm, and that Yusuf’s hand had closed over hers at some point she could not reconstruct and had not moved since.
Neither of them moved it. They floated there, not touching anything else in the universe, weightless, in violation of a policy with forty-one days to run, over a console showing a seven-nanometre step in a mirror two million times too delicate for anyone’s hands.
— This is holding on to each other, said Yusuf, after a while, in a tone of scrupulous technical accuracy. Which is, I’m told, the entire available envelope.
— It’s a handrail.
— It’s a shared handrail.
— Dr. Tanrıkulu.
— Forty-one days, he said, and did not let go, and did not do anything else either, and from the far console, without turning around, Kwabena said:
— I’d like the record to show that I have seen nothing, that I am an unreliable witness, that the cabin camera has been inoperative since Tuesday because I unplugged it on Tuesday, and that if either of you gets us written up over a handrail I will personally tell Dr. Volk about the coffee.
⁂
It was fifty-three days. They spent most of them going home.
The frame arrived four weeks into the cruise, relayed up with a note from Volk consisting of a single character, a colon followed by a bracket, which Ileana printed and taped to the bulkhead.
The star was a point. Not a perfect point — nothing is, and the diffraction rings sat where theory said, patient and concentric, the honest limits of a real aperture doing its best with real light. But the collar was gone. Around the core there was only the structured dark of a well-made instrument looking at a sky that had never been soft at all, and had only seemed so for a while, to three people standing too close.
— Threshold’s clear, said Kwabena. Contrast two point one times ten to the minus ten.
Better than before they arrived, by a little over six percent, because the bake-out had taken six years of slow accumulation along with their nineteen days of enthusiasm. Nobody had planned it. It is what happens when your own mess forces you to clean something more thoroughly than any committee would have authorised.
It did not give back the year. Ileana did the arithmetic once more and wrote it into the final report in the flattest sentence she could build, having decided somewhere over the last hundred million kilometres that the one honest thing she could do with the cost was refuse to make it sound smaller than it was. The observatory would end a year early. 82 Eridani would be observed in nine years by whoever was on console. She would be fifty. There was an ocean there and she was not going to be the one to see it, and she found, examining the feeling with some interest, that it hurt about as much as she had expected and did not hurt in the way she had feared, which are two different measurements and only one of them had been in the model.
Three weeks later, with the new detector running, Threnody returned a spectrum of GJ 1002 c in a single night that would have taken a week before, and the water bands came up so hard and clean that the discovery team spent an hour convinced they had a calibration error.
— Put it on the stamp, said Kwabena.
— They already did, said Yusuf. It’s a terrible photograph.
— My face has always been involved.
Ileana looked at the frame a long time, at the sharp hard honest outline of a thing that had been there the whole while, and then at the mission clock, which read six days to atmospheric entry and the formal end of an assignment, after which Policy 9.2 would have nothing further to say to anybody.
— Worth starting, then, she said.
Sixty-Four Pascals
The first thing Teodoro Quispe did on the surface of the asteroid was turn a screw, and the screw turned him.
He had the anchor seated and the driver braced and he squeezed the trigger, and the anchor went in, and Teodoro began — slowly, evenly, with tremendous dignity — to rotate in the opposite direction. His boots came off the ground at about the same moment he understood what was happening. He went round once in nine seconds. He went round again.
— Ritsuko.
— Mm.
— Any time.
— I’m filming.
— I can see that you’re filming. I can see the light.
— It is an unanticipated dynamics case, said Ritsuko Amagai, four metres away, not moving, — and we are required to document those.
— It is me, going round.
— Those are compatible, said Ritsuko.
From eight hundred metres above them, in a vehicle that had not landed because there is no landing here, Zofia Marchlewska said:
— Let the record show that I warned both of you about this exact thing at the exact angle, and that nobody listened, and that I have now been proved right inside the first hour of the first excursion, which is early even for me.
Teodoro got a hand on the tether and stopped himself, which took two attempts, because pulling on a line also pulls the line, and the line was attached to Ritsuko’s anchor, so that for a moment the two of them drifted gently toward each other like a pair of balloons in a stairwell.
— Hello, said Ritsuko.
— Don’t.
⁂
The object underneath them was a kilometre and a third of loose rubble that had no business existing.
It turns once every two hours and seven minutes, and that is the whole problem. Spin a heap of gravel that fast and the material at its waist is flung outward harder than the heap’s own gravity pulls it in, and the correct and dignified behaviour is to come apart — to throw the equator off into a ring and settle down to a decent speed like everything else in the catalogue.
It has not come apart. It has been doing this for an extremely long time.
— So what’s holding it on, the flight surgeon had asked, four years earlier, at the medical briefing, which is not where this question normally comes up.
— Dust, said Ritsuko. The grains are holding hands.
— That’s a metaphor.
— It is not remotely a metaphor, said Ritsuko. Two grains of rock touching each other attract. It is the feeblest effect in the entire inventory, it would not hold up a postage stamp on Earth, and there are something like ten to the twentieth of them down there, and the sum is a mountain. We would like to know the number to better than a factor of three, because in eight hundred and fifty years this thing may hit us, and what we are permitted to do about that depends entirely on how hard you are allowed to push it.
— And you can’t measure that from a spacecraft.
— We can measure it from a spacecraft to a factor of six, said Ritsuko, — which is the difference between a plan and a hope.
⁂
Nobody sleeps properly out there, and the reason is daylight.
The Sun comes up in the west, because the thing turns backwards, and the whole of morning takes ninety seconds. There is an hour of day, two minutes of evening, an hour of night, and then it all happens again, for ever, twelve times between breakfast and bed. Teodoro’s body refused to sign the agreement. Three weeks in, with the shutters down and the lamps off and ship’s time painted on every surface, his eyes would still open at random intervals and ask, with great sincerity, what time of day it was outside.
— That one, Zofia would say, from the flight deck, without looking. In ninety seconds.
On the fourth week he gave up and went to the window during a night, and watched the terminator come over the horizon at a brisk walking pace, and the shadows of the boulders shorten visibly, like something going out of focus in reverse, and said afterwards that he had stopped minding and had begun to find it restful, which Ritsuko said was the most alarming thing he had told her in twenty-two years.
What neither of them ever got used to was the sky, and specifically that it moves.
The whole heavens go round in two hours and seven minutes. Lie on your back on that surface for sixty seconds — which you can, because there is nothing to stop you, and because lying down is in any case the most practical posture available — and you can watch Orion slide. Teodoro had grown up at four thousand metres with the best night sky on Earth over his head and had spent a childhood unable to catch it moving.
— That’s the thing, he said, on the loop, flat on his back, tethered, in the middle of a work shift, doing nothing at all. That’s the thing I’m going to miss.
— You are on the clock.
— I am aware of the clock.
— You are on the clock and you are lying down.
— Ritsuko. The sky is going round. Lie down.
There was a pause of about four seconds.
— I’m lying down, said Ritsuko.
— I know. I can see your boots.
— You can see my boots because my boots are off the ground, said Ritsuko. Everybody’s boots are off the ground. It is the condition of the place.
⁂
Here is what the place weighs.
A man of a hundred and eighty kilograms, counting his suit, weighs about five grams at the poles of this object. Five. A moth. A small coin. You cannot walk, because walking requires something to push against and you have nothing to push with; the first push sends you off the world, since a stroll — twenty-two centimetres a second — is escape velocity.
So they crawled, and clipped, and installed handholds as they went, and did everything against an anchor, because every single action moves you exactly as much as it moves the thing you are acting on, a sentence that every one of them could have recited at sixteen and that none of them had ever had to live inside.
Zofia hovered. She did not orbit, because close orbits around a fast-spinning lump go chaotic in days: the gravity field of an irregular body is lumpy in its own right and it turns underneath you. So Sestina station-kept on tiny pulses at eight hundred metres, nose down, for fourteen weeks, which Zofia described as holding a ladder for two geologists and about as intellectually demanding.
— You have a doctorate, said Teodoro.
— I have a doctorate and I am holding a ladder, said Zofia. These are the two facts and they are both true and I have made my peace.
The agency, incidentally, continues to name its deep-space vehicles after verse forms, and the committee responsible has now worked its way down to the ones that cannot be explained without a diagram. Zofia had looked up what a sestina actually is, in week two, out of boredom, and had regretted it, and had explained it to the other two at dinner, at length, with a napkin, and the unanimous verdict afterwards was that the committee had lost control of the situation some years ago.
⁂
The horizon was forty-seven metres away.
That is not a turn of phrase. On a body this small, with your helmet a metre and a half up, the ground curves out of sight at about fifty paces in every direction, and past that edge there is nothing at all. You stand on a small grey hill that stops. And because the hill stops, the sky does not: it comes all the way down and round and continues underneath, so that from the middle of a flat area you can walk forty metres and look down, past your own boots, at stars.
Ritsuko walked to the edge on the ninth day to place a reflector and stood there longer than the task required.
— You’re quiet, said Zofia.
— I’m at the edge of the world.
— Is it nice?
— It’s about four metres from the reflector mount, said Ritsuko, — and it is the actual edge of the actual world, and I can see the Pleiades underneath my feet, and I would like one minute, please, before I am a professional again.
She got the minute. Teodoro, who had the other end of the survey line and could have filled the silence, did not fill it, and mentioned it to nobody, and that is the first thing in this story that was going on without being said.
⁂
The ground was made by light, and so was everything else, and this was the part Ritsuko kept coming back to.
There is no weather. There has never been weather. The regolith underfoot was manufactured by sunrise: the Sun comes up every sixty-four minutes, the face of a rock goes from a hundred and seventy kelvin to three hundred and forty in a few minutes and back again, and it does that eight thousand times a year, and after a billion years the rock gives up and becomes gravel, and after another billion the gravel gives up and becomes dust.
And the dust clings.
That is the most memorable physical fact of the place, and it is best demonstrated with a hand.
— Hold out your glove, said Ritsuko, on the second week.
— Why.
— Because I am about to put something in it and I want to watch your face.
She scooped up a double handful of fines and poured them onto his palm, and they did not pour. They arrived in a grey clinging mass like a wasp’s nest, and when Teodoro turned his hand over, slowly, they stayed. They hung from the underside of his glove in a sagging lump that moved when he moved and did not fall, because out here, at the scale of a grain, weight has left the argument entirely and surface forces have taken the whole thing over.
— Oh, said Teodoro.
— Yes.
— Oh, that’s — yes.
— That is the entire object, said Ritsuko. That is the force. The thing you are holding is the reason there is a floor.
He tipped his hand back and forth a few times, which did nothing, and then held it out toward her, and she took some of it off with her own glove, and for about two seconds their hands were in contact through two layers of pressurised fabric in a way that was completely necessary and lasted slightly longer than it needed to, and then they got on with the survey.
Zofia, eight hundred metres up, with nothing to do but hold a ladder and watch two camera feeds, said nothing at all, which cost her something.
⁂
The method was to hit the asteroid and listen to it.
They laid sixty metres of geophones across the north polar region, each one screwed down and levelled, which took four days, because every screw had to be driven against a reaction mass after the lesson of the first hour. Then they shot the surface with a spring gun, because a dropped weight here takes a minute and a half to fall one metre and you cannot run a seismic survey on that schedule.
The first shot told them most of it.
— That’s it? said Zofia. That little thing?
— That little thing, said Ritsuko, watching the trace, — is a signal that went into the ground, travelled about twelve metres, and gave up.
— Which means.
— Which means it is exactly as loose in there as we thought. Poorly contacted, voids throughout, and it carries a shock the way a sack of walnuts carries one.
The video was the part they watched forty times, and then showed to Earth, and then watched again.
The surface did not crater. It splashed. There was a brief grey hump and then a slow spreading ring, lifting, drifting outward at a few centimetres a second, every particle on its own small ballistic career, and then nothing happened for five minutes, and then it all came down again, gently, more or less where it had started.
— It’s a ball pit, said Zofia.
— It’s a ball pit where every ball is glued to its neighbours with about the weight of a postage stamp, said Ritsuko, — which is why it is a ball pit and not a cloud.
They shot it thirty-one more times over five weeks and at the end of it they had a number, and the number was sixty-four pascals. The pressure of a sheet of paper lying on your hand. That is the thread the mountain hangs by. Ritsuko refused four separate requests to tighten the uncertainty and the planetary defence office accepted the figure in the form it was offered, which from that office is a standing ovation.
⁂
Then they went to the equator, where down is up.
The arithmetic turns over at the waist. Gravity pulls in; the spin throws out; the throw is bigger; and the difference, going the wrong way, is about a hundred-thousandth of Earth’s gravity, outward, everywhere, all the time. Let go of a pebble there and it does not fall. It rises, unhurriedly, and keeps rising, and does not come back.
— Describe it, said Zofia, on the first equatorial excursion, because she had asked twice already and had been told twice that it could not be done.
— It is like the top of a lift, said Teodoro. The moment at the top of a lift when your stomach is still coming up.
— Everybody says that.
— Everybody says it because it is right. But the lift stops and this does not stop. It goes on for four hours. You are being very politely pushed off a hillside from underneath, continuously, by the ground, which is not quite strong enough to do it and has not stopped trying for four and a half billion years.
— And you’re sure you’re not simply frightened.
— I am certainly also frightened, said Teodoro, — but the feeling in my stomach is correct and has a value and I could write it on the board.
The equatorial ridge is the one part of the object that is unarguably beautiful. It is a raised band running the whole way round the waist, which is not a mountain range but a tide mark: as the spin crept up over the ages, material crept toward the equator, and it is creeping still, and the ridge is the record of a body in the slow act of throwing itself away.
They had been there three hours, and had placed four anchors, and Ritsuko had just started the fifth, when Fifteen let go.
⁂
Fifteen was a boulder about nine metres across. It was called Fifteen because by then nobody had the energy to be imaginative. It had been sitting in that spot for some substantial fraction of the age of the Sun, held on by the same sixty-four pascals as everything else, and what dislodged it was not the drill. It was four anchor installations inside twelve metres, each one breaking a few thousand grain contacts, in a place where everything was already being pushed outward.
It did not roll. It did not topple. It rose.
A piece of rock the size of a chapel came off the surface of an asteroid, evenly, in complete silence, and started up into a black sky at about the speed of the minute hand of a large clock.
— Up, said Teodoro.
Then nothing from him for two whole seconds, which is the longest he has ever been silent at work.
The horror of the next ninety seconds is entirely in the slowness, and it has to be laid out properly or it sounds like nothing at all.
The boulder was accelerating at about a ten-thousandth of a metre per second squared. In the first minute it rose twenty centimetres. In two minutes, eighty. It could not have crushed anybody; at those speeds it would have pressed a person into the regolith about as hard as a duvet presses you into a bed.
The tether was the problem. Ritsuko’s line ran from her waist, under the base of Fifteen, to the screw anchor on the far side. As the rock came up it was lifting the line with it, and when the line came taut she would be pulled off the equator of a rotating asteroid, attached by six metres of webbing to nine metres of departing stone, with a combined mass that nothing in her possession could argue with, leaving for ever.
Zofia’s reconstruction gave her between seventy and a hundred seconds.
And she could not run. That is the thing that has to be understood. There is no running. The push required to move her three metres sideways in a useful time is the same push that launches her off the surface, where escape speed is an amble and the ground was already helping.
— Cut it, said Teodoro.
— Working along it, said Ritsuko, who had already pulled the slack and was hand-over-handing toward the anchor, and who abandoned that four seconds later because the line was going up with the rock and taking her hand with it.
— Ritsuko. Cut it.
— If I cut it I have nothing.
— If you keep it you have nine metres of rock.
— I’m aware of the rock.
— Ritsuko.
— Don’t say my name like that, she said, — it makes it harder.
She unclipped.
There is no procedure in which you unclip. The tether is the entire relationship between a human being and a body they cannot stand on, and unclipping at the equator of this one — where the ground is quietly trying to put you into interplanetary space — is, as the report later said with admirable restraint, outside the envelope of recommended practice.
The line went away over her head with Fifteen, unhurried, almost ceremonial.
And Ritsuko Amagai lay down flat on her front and took two handfuls of dust.
That is the whole manoeuvre. That is why there is a story instead of a memorial.
She needed about a fiftieth of a newton to stay on the surface — two grams, in Earth terms. The dust she was holding had been holding a kilometre-wide mountain together against a two-hour rotation since before the Earth had a crust, and it was more than equal to a geologist. She lay with her fingers pushed into the fines to the second knuckle, boots off the ground, legs drifting up slowly behind her like weed in a current, held on by surface chemistry, while a chapel went up past her shoulder and kept going.
— Status, said Zofia, in a voice like a sheet of steel.
— Holding on.
— Holding on to what.
— The force, said Ritsuko.
Teodoro reached her at ninety-four seconds with a second line, properly anchored, hand over hand. He has described those ninety seconds exactly once, and not as frightening — there was no violence anywhere in it — but as obscene: like running underwater toward somebody in a dream, with everything in his body screaming for a speed that the universe had simply declined to supply.
Fifteen is still going. It is in its own orbit around the Sun now, a nine-metre rock that sat on an asteroid for four billion years and left because three people put some screws in the ground nearby. Ritsuko named it in the log. She called it Postage Stamp. The Minor Planet Center has been very patient about the paperwork.
Afterwards, in the airlock, with the suits still on and the pump running:
— You said my name like that on purpose, she said.
— I did not.
— You did it twice.
— The second one was not on purpose, said Teodoro.
⁂
Hirut Alemayehu ran the planetary defence office and had not got there by being soothing. Her instruction had arrived before launch and had made both of them furious in the quiet way that lasts.
— Two assessments, independently produced, she had said, over a six-minute light time. I want them to disagree. If they agree in every particular I shall want to know which of you stopped thinking first, and I will find out, because I have read twenty-two years of your papers and I can hear both of you in every sentence of them, including the ones with only one name on top.
— That’s insulting, Teodoro had said, to a screen.
— That is a procedure, Ritsuko had said, and had gone quiet.
— It is insulting and a procedure, Zofia had said, from the flight deck, not turning round. People underestimate how often those overlap.
So, after the survey, they were separated for six days. Ritsuko in the lower bay, Teodoro on the flight deck, no discussion, with Zofia enforcing it in a manner the two of them found hilarious for about three hours and then did not find hilarious at all.
On the first morning Ritsuko opened a blank page to derive the cohesive strength from scratch, which she had done in collaboration perhaps forty times and which she expected to take four hours.
The route is not complicated. You take the spin rate, which is measured to absurd precision. You take the shape, which the radar gives you. You take the bulk density, and from the bulk density and an assumed grain density you get the porosity, and from the porosity and the spin you get the stress state at the equator, and the cohesion is whatever has to be there for the thing not to have come apart.
The bulk density needs the mass, and the mass comes out of the astrometry, and the astrometry has a drift term in it, because the orbit of this object is being pushed by its own radiated heat, and the size of that push depends on the thermal inertia of the surface.
Ritsuko typed the symbol for thermal inertia and stopped.
She had used that number in fourteen published papers. She could see its value — she could see the font it was in, in the table, in the 2047 paper, third row — and she had never once derived it, or checked the pipeline that produced it, or been in the room when the regolith conductivity scaling was argued about, because that was Teodoro’s, had always been Teodoro’s, for twenty-two years, the way the strain tensor had always been hers.
She sat with her hands off the keyboard for a while.
Then she went and got the raw thermal data and started on it herself, and by the second day she had established that she did not know how to do it. Not that it was difficult. She could read the method. She could follow every step in his paper. What she could not do was form an opinion about it — could not tell, looking at a choice between two conductivity models, which one would annoy her, which is the only reliable instrument any scientist actually has, and the only one that cannot be lent.
On the third evening she wrote in her notebook, in pen, and then tore the page out and then put it back in: I have published forty-one papers. I can defend about twenty-six of them.
Up on the flight deck, Teodoro’s problem arrived in a different costume and was the same problem.
He wrote a clean paragraph on the second day and read it back and heard her in it. Not the content — the shape. The habit of stating the objection first and answering it second. The dashes. The way a sentence would set up a measurement and then undercut it with a clause beginning which is. He had been writing like that for fifteen years and had always assumed it was his.
He deleted the paragraph. He wrote it again in what he believed to be his own voice and it came out sounding like a second-year student, flat and over-explained and slightly pleading, and he looked at it for a long time, because the honest conclusion available from the evidence was that his own voice had stopped existing somewhere around 2045 and nobody had sent a notice.
On the fourth day he found, in his own handwriting, in a notebook from 2043, the sentence about strain partition that he had been giving in talks for a decade as his own observation, and could not establish whether he had written it down because he had thought it, or because she had said it at lunch and he had wanted to keep it.
He took that to Zofia, because there was nobody else, and because by then he had decided that the rule against discussion covered the asteroid and not the catastrophe.
— Ask me a question about rubble piles, he said.
— No.
— Ask me anything. I want to see whether there’s anybody in here.
Zofia put down what she was holding, which was a pen, and turned round in the seat, which she did not often do.
— I’ll do better than that, she said. Sit down. I am going to tell you something and then I am going to go back to work and we are never going to discuss it.
Here is what Zofia Marchlewska did, every hour of every day, for fourteen weeks.
She held a vehicle eight hundred metres off a lumpy rotating rock whose gravity field turns underneath you and cannot be trusted past a few hours. The autopilot handles the arithmetic and does not handle the judgement, because the judgement is about which of the model’s assumptions has quietly stopped being true, and no autopilot has an opinion about that. So every few minutes, for fourteen weeks, she made a small decision that nobody checked, with the nearest second opinion six minutes away at the speed of light, about an object that would eat the three of them in silence if she got a sign wrong.
She keeps a paper log. In pen. Not because the systems do not record everything, which they do, but because she worked out at thirty-one that she needed to say her reasoning out loud to somebody before acting on it, and there has never been anybody, so she says it to a notebook. She has fourteen of them at home. Her sister thinks they are diaries.
— Nineteen years, she said. I am extremely good at this and I am completely alone inside it, and I decided at twenty-six that I could not afford to be otherwise, because the thing that keeps me alive out here is that there is exactly one person in the loop and I know precisely where her edges are.
— Zofia —
— I have not finished. I have spent fourteen weeks watching the two of you and I have been making jokes about it, and the jokes are real, and underneath them I want to be clear that there are two things in my head at once and they do not resolve.
— Go on.
— The first is that what you two have is the thing I gave up and I have watched it with my face pressed against the glass for three months, said Zofia. You get to be wrong in front of somebody. Do you have any idea. You get to say a stupid thing out loud at two in the morning and have it come back improved. I say my stupid things to a notebook and the notebook never once argues.
— And the second thing.
— The second thing is that I think what you have done to yourselves is dangerous and that I would not survive it, said Zofia. If I lost half of my judgement to another person I would fly this vehicle into that rock inside a week. I need all of mine, all the time, and it has to be mine, and it has to be the same instrument tomorrow as it was today. You have built something magnificent and you have built it out of the only tool either of you brought, and the office is right, and you are going to hate me for saying so.
— I don’t hate you for saying so.
— Give it until Thursday, said Zofia, and turned back to the panel, and did not discuss it again for the rest of the mission, except once, four months later, when she asked Ritsuko to read a page of her log and tell her whether the reasoning was sound, and Ritsuko said that it was, and Zofia said thank you in a voice that neither of them commented on.
⁂
The assessments came in on the sixth day.
The numbers agreed inside the error bars, which Hirut said afterwards she had expected and would have been alarmed not to see, because data are data. The recommendations did not agree at all, which is what the six miserable days had been for.
Here is the fork, both arms of it, neither comfortable.
If the body is strong, you may push it. Hit it, or better, shove it slowly, and change its speed by a few millimetres a second, which over eight centuries is the width of a planet, and it goes by.
If the body is weak, you may not. A rubble pile glued together with tens of pascals does not take an impulse the way a rock does: it absorbs it, deforms, redistributes it, and may shed a fraction of itself, and then the single object you started with is a loose swarm on slightly different orbits, spread along the track, some of which are still coming. Trading one impact for an unknown number of smaller ones over a wider area, with a hundred times the tracking problem, is not obviously a trade.
Sixty-four pascals is weak. They agreed on that.
Teodoro’s proposal was the gravity tractor. You build a vehicle with as much mass as you can afford and you fly it alongside the asteroid, a hundred metres off, for thirty years, firing continuously and canting the thrusters outward so the exhaust never touches the surface. The ship pulls the rock with nothing but its own gravity — a force of a fraction of a newton, less than the weight of an apple, applied without pause for three decades. Nothing is struck. Nothing is disrupted. You simply stay beside it, not touching it, burning fuel the entire time, for longer than most marriages, and at the end of it the thing has moved.
Ritsuko’s proposal was a kilogram of chalk.
Not literally chalk: a reflective dust, delivered in a single pass, laid over a fraction of the surface, altering how that surface takes up and lets go of heat. The object’s orbit is already being steered by its own radiated warmth and has been for four and a half billion years. Change the surface and you change the steering. One pass. One release. Then you go home, and sunlight does the work, and in eight hundred and fifty years the thing is somewhere else.
Zofia read both documents in one evening and said the thing that neither of them had allowed themselves to say.
— You’ve each proposed yourselves.
— That’s glib, said Ritsuko.
— It is extremely glib and I have been holding a ladder for fourteen weeks and I have earned one, said Zofia. His is a machine that stays next to the thing it loves for thirty years, never touching it, under power the entire time, and calls that a solution. Yours is a handful of dust thrown once and then nothing, no contact, no presence, no control, trusting a slow process to do it properly if you only leave it alone long enough.
There was a silence in which the air handler could be heard.
— The objection to mine, said Teodoro eventually, to the table, — is cost.
— The objection to yours, said Ritsuko, — is that it has to be maintained for thirty years by people who will not be the people who started it.
— And the objection to yours, said Teodoro, — is the one you have not written down.
Ritsuko did not answer at once.
The objection to hers is this. If you throw the dust and go home, nobody alive will ever learn whether it worked. The encounter is in 2880. Every measurement you can make in your lifetime will be consistent with success and consistent with failure, because the signal is a drift of metres per year against an uncertainty of kilometres, and the answer arrives in a century with nobody in it that you ever met. You do the one small irreversible thing, and then you spend the rest of your life not finding out, and so does everyone you will ever love, and the first person who knows is a stranger eight hundred and fifty years downstream who will not know your name and will have no reason to.
— I am aware of it, she said. I prefer it anyway.
— Why?
— Because it is true of nearly everything, said Ritsuko, — and most people arrange their lives so as not to notice, and I would rather not, and also because it works, which is the part you keep leaving out of the question.
Hirut’s office took eighteen months and adopted a programme combining both, because the two methods fail in different directions and the combination is robust, which is what offices are for on the rare occasions they work.
Her covering note was not part of the official record and both of them kept it.
— Dr Amagai’s recommendation is the more elegant and Dr Quispe’s is the more likely to be funded. Your two documents disagree about the method and agree about the data, and it took six days of not speaking to each other to produce that. Please do it on purpose from now on. I am sorry about the six days. I am not sorry enough to withdraw the instruction.
⁂
The cruise home took four months, which is a long time in a small vehicle with somebody you have just been forbidden to talk to.
Ritsuko had kept a sample tube of the fines from the equator — the dust that had held her on — and she had it out in the lab in the ninth week when Teodoro came in.
He stood in the hatch for a moment, which he did not normally do.
— I have been composing a sentence for two months, he said, — and I am going to say it badly.
— Say it badly.
— I can no longer tell which parts of me are mine, he said. And for six days that frightened me, because the office was right and it is a real defect. And I have spent two months waiting for the fright to arrive properly, and it has not come, and what came instead is that I don’t want it fixed. I want it managed. I would like us to go on being one instrument with two readouts, and I would like somebody to put us in separate rooms every single time anything matters, for the rest of our working lives, and I would like it written into the proposals.
Ritsuko turned the tube over in her hand.
The dust inside did not pour. It clung to the glass and came away in slow reluctant sheets, weighing nothing whatever, held on by the feeblest force on the list, acting across a number of tiny contacts that nobody has ever counted, exactly as it had been doing on the waist of a mountain for four and a half billion years without once being asked and without, as far as anyone can establish, ever having been thanked.
— Do you know what this does on Earth, she said.
— Tell me.
— Nothing. It becomes dirt. The force is still there — it doesn’t switch off, it is a property of matter and it goes on acting in your kitchen exactly as it acts here. It simply stops mattering, because down there everything is being pulled on some thirty thousand times harder, and there is water in the air that gets into every contact, and the grains slump into a heap like any other heap and you sweep them up. In a laboratory on Earth this tube is a soil sample. Nobody would look at it twice.
— That’s a depressing fact about Earth.
— It is a fact about competition, said Ritsuko. The force never changes. Sixty-four pascals holds up a mountain here because there is nothing else pulling, and down there it holds up nothing at all, because everything else is pulling. That is the whole of it. There was never anything special about the bond. There was only a place with nothing in it to interfere.
She put the tube back in the rack.
— Agreed, she said. Separate rooms. Write it in.
And neither of them said the other thing, then or afterwards, and they worked together for nineteen more years, and took three sabbaticals in the same institute without ever once arranging to be in the same city outside working hours, and the dust is in a drawer in Tokyo, where it is dirt.
Nothing Is Where You Left It
The lander was supposed to come down at 04:12, and at 04:12 it did not come down, and the thing Caio Bettencourt remembers is that it was beautiful.
He was out on the rim with Imane Benali, both of them suited, in the light that the lunar south pole does and nowhere else does. The Sun sits a degree and a half above the horizon and goes round it instead of over it, so nothing is ever overhead, and every pebble throws a shadow a hundred times its own length, and the whole landscape is drawn in horizontal light like a stage lit from the wings by somebody with strong opinions. The shadows swing. Over a month they come round like the hand of a clock, and after a while you stop checking the time and look at which way the boulder outside the workshop is pointing.
Kittiwake came over the western horizon on schedule, a hard white star moving fast, and lit its engine for the descent burn, and the plume was a small silent cone of light that should have grown and steadied and brought sixteen tonnes of water down the last fifteen kilometres onto the pad.
It burned for nine seconds. Then it stopped.
The star went on across the sky at the speed it had always been going, which is the speed of a thing in a hundred-kilometre orbit, unhurried and entirely indifferent, and it crossed the whole black sky in four minutes and went over the eastern horizon, and the sky was empty.
— Well, said Imane.
— Yes.
— That’s ours.
— It’s ours.
— It’s ours and it’s going round, said Imane, and she said it the way you say a word in a language you are learning, to hear whether it sounds as bad out loud as it did inside.
⁂
The question everybody on Earth asked, in the fortnight that followed, usually in the first sentence and usually with a small laugh in it, was why four people sitting on the largest ice deposit in the inner solar system were short of water.
It is a fair question and it has an answer and the answer is concrete.
— They think it’s a rink, said Oskar Lindqvist, who ran the workshop and who had been asked it twice by journalists and once by his own brother. They think we chip it with a pick and put it in a bucket. My brother asked me whether we could skate.
— What did you tell him?
— I told him to go out to his garden, said Oskar, and dig up a cubic metre of frozen clay with a spoon, and then pick the frost out of it, and then write to me about the ninety kilograms of water he had not obtained.
The ice at the pole is not ice. It is frost, mixed through the regolith at something between a half and a few percent by mass, in the top metre or two of a crater floor that has not seen sunlight since before there were continents, and at forty kelvin that soil is not soil. It is cemented. It has the mechanical character of a poor concrete and it does not care about hand tools. To get a tonne of water out of it you must excavate and heat somewhere between thirty and two hundred tonnes of the stuff, in the dark, at forty kelvin, where lubricants turn to wax and batteries die and every machine you own is operating a hundred and eighty degrees below its design intent, on power that comes down a cable from a ridge four kilometres away because there is no sunlight to put a panel in.
The machine that did this at Rim Nine was called the plant, and the plant had been down for nineteen days, and the reason the plant was down was a drive train that had eaten lunar dust, which is what lunar dust is for. The bearings were on the next cargo flight. The next cargo flight was Kittiwake.
And the reason the margin mattered at all — the reason there was not a comfortable buffer sitting in a tank while they waited — was the thing that had happened ten days before that, which Thanh Dieu Nguyen still referred to, with great evenness, as the event.
The stored water lived in two tanks in the cold shade under the north berm, which is the sensible place to put water on the Moon: no sunlight, no boil-off, no pumps. What nobody had modelled properly was the thermal cycling on the support saddles as the shadow swung round through the lunar month, and a weld that had been quietly working itself to death for three years gave up at some point during the night side, and sixteen tonnes of water sublimated into vacuum over about six hours, silently, invisibly, into a sky that did not notice.
There is no puddle. That is what Caio could not stop thinking about for a week. On Earth a disaster like that leaves a lake and a smell and a mess you can stand in. Here it simply stopped existing, and the only evidence was a gauge, and the gauge took six hours to go from everything to nothing, and the crew slept through four of them.
Kittiwake was the answer to the event. Kittiwake was the rescue. That was the part the journalists kept missing: the base had not run out of water and then had bad luck. The base had run out of water, and help had come, and help was now in orbit.
Thanh put the numbers on the galley screen inside the hour, worst first, as she did.
— Open loop, four of us, hard ration, no washing, the backup recycler doing what it can: nine days. Oskar’s quarry adds five if it keeps producing. Earth’s emergency flight is twenty-two days out and that is optimistic and everyone in this room knows what agency optimism weighs. Kittiwake is four hundred kilometres over our heads with sixteen tonnes, and it is going round every two hours, and it does not answer.
— Then we go and get it, said Oskar.
— Yes, said Thanh. That is the whole of the discussion and it took about six seconds. The rest of the week will be us finding out it is not that simple, and the reason it is never simple is that it is in orbit, and orbit does not work the way the inside of your head works.
Over the suit racks in the workshop, in letters Oskar had cut from scrap aluminium in his second month and that nobody had ever persuaded him to take down, was the sign:
IF IT FEELS RIGHT YOU ARE ALREADY IN THE WRONG ORBIT.
⁂
Oskar’s quarry deserves its own paragraph, because it ran all the way through the fortnight and because it was the only funny thing happening.
On day two he had taken a jackhammer, a resistance heater, a cold finger, a tarpaulin and a quantity of improvised plumbing down the cable run into the permanently shadowed floor, and had begun to mine the Moon by hand. The procedure was: break out a barrow of frozen regolith, bag it, drag it under the tarpaulin, heat it with the resistance element, catch the vapour on the cold finger, scrape off the frost, melt, filter, repeat. It worked. It worked at a rate of between eight and fifteen kilograms a day, depending on whether the patch he had reached was rich or poor, which nothing on the surface tells you in advance.
The crew needed about twelve.
— So we’re fine, said Caio, on the fourth evening.
— We are fine, said Oskar, in the sense that a man running down a corridor with a bucket under a leaking roof is fine. It is thirteen hours a day in the dark at forty kelvin. My suit’s glove heaters are at maximum the whole shift and my hands are still cold, because the ground is a hole that heat falls into. The hammer has started making a noise I don’t like. The cold finger is a thermos lid. And the production rate is a coin toss on every barrow. I have found patches at four percent and patches where I heated a hundred and ten kilos of rock to get a glass of water.
— You’ve also lost six kilos.
— I have lost six kilos and gained a trade, said Oskar. On Earth I am an engineer. Here I am the only miner on the Moon, and I would like that in the record, and I would like a hat.
He got a hat. Imane made it out of thermal blanket offcuts on the seventh evening and it was awful and he wore it in the galley for the rest of the deployment.
⁂
Caio walked out to the pad on the eighth day to run a pre-flight on a vehicle he was trying not to think about, and stopped halfway, as he always did, because of the view, which does not get less strange and which nobody had described to him adequately before he arrived.
The first thing is that the ground ends.
A man’s eyes on the Moon are about a metre and a half up and the Moon is a small world, so the horizon is two and a half kilometres away. Not hazily, not approximately: two and a half kilometres, and then an edge, and then black. There is no distance beyond it to look into. On Earth the far-off is always doing something — haze, blue, a suggestion of hills — and here the world is a bright disc of rubble about five kilometres across with a man standing in the middle of it and nothing whatsoever past the rim. It is the clearest possible demonstration that you are standing on a ball, and it never once reads as beautiful on the first day. It reads as an error.
And then, out past the edge, with nothing underneath them, there are mountains.
Those are the far ridges, forty and sixty and a hundred kilometres off, whose tops come up over the curve while their bases are hidden below it. They sit in the black, lit along one side, apparently afloat. There is no air to grey them with distance, so a peak ninety kilometres away is exactly as sharp as the handrail by the hatch, and the brain, having no cue to go on, puts it wherever it likes and changes its mind hourly. Oskar had set out on his second week to walk to a rock, with a clear idea that it was a chest-high boulder a few hundred metres off, and had been called back by Thanh after twenty minutes when it became obvious from his helmet feed that the rock was twelve storeys tall and over a kilometre away and was in fact slightly larger than the habitat.
The Sun does not rise here and it does not set. It goes round.
At this latitude it sits on the horizon the whole time, a degree or so up, and tracks right the way round the compass over a month, and there is no noon. It is permanently dawn and permanently dusk, from every direction in turn. The ridges that stand high enough catch it almost continuously — the old astronomers called them the peaks of eternal light, which is florid and is also exactly correct, and is why the power plant is up on one of them and the people are not.
The sky is black with the Sun in it. That is the part the photographs cannot do. There is no air to scatter light, so there is no blue, no glare, no brightening around the disc: the Sun is a small ferocious white circle and the sky touches it and is absolutely black at the point of contact, like a hole burned in cloth. Nothing is diffused. Every shadow has an edge you could cut a finger on.
And the shadows are long. At a Sun angle of one degree, a boulder a metre high throws a shadow sixty metres long, and the workshop throws one most of the way to the quarry road, and all of them sweep round through the full circle over the month like the hand of an enormous clock laid flat on the ground. Everybody at Rim Nine tells the time by looking at which way the boulder outside the workshop is pointing. Everybody does it unconsciously within about three weeks. Oskar had painted the hours on the ground around it and the paint had been a failure, because paint on the Moon is a brave idea.
There is a thing that happens around the shadow of your own head, and Caio had never read about it anywhere and had been quietly delighted by it for eight months.
When you look at the ground directly away from the Sun — at your own shadow — there is a soft halo of extra brightness around the shadow of your helmet, a glow a few degrees across that falls off smoothly outward. It is not a trick of the eye. Looking straight down-Sun, every grain of dust hides its own shadow exactly behind itself, so that patch of ground is showing you nothing but lit surfaces, and it genuinely is brighter. It follows you. It stays centred on your own head, forever, wherever you walk.
And you cannot show it to anybody. It is centred on the observer, so Imane walking beside him has her own, over her own shadow, four metres away, and from where Caio stands hers is not there at all. Oskar maintained that this proved something theological. Imane maintained that it proved that light goes in straight lines. Thanh had ruled that they were not to have the argument on the suit loop any more because it was being transcribed by the agency.
The colour of the place depends entirely on which way you are facing. Down-Sun, with your own shadow in front of you, the regolith is a warm tan brown and looks almost like soil. Turn ninety degrees and the same ground is a dead neutral grey. Turn to face the Sun and it is nearly white with a dark fringe on every rock. Nothing has changed except the geometry of how the dust is hiding its own shadows from you, and the Moon obligingly changes colour three times while you turn round on the spot, which is the kind of behaviour that makes people say the Moon is grey and makes everyone who has been there say it depends.
Four kilometres north, the ground stops being lit at all.
The permanently shadowed floor does not read as darkness, because darkness is something you look into. It reads as a hole in the data. The Sun has not touched it since before there were fish, the rock down there sits at forty kelvin, and from the rim in sunlight your eyes are so adapted that the floor is simply absent: a shape cut out of the Moon with scissors, with Oskar somewhere down inside it, on a cable, in a hat, mining frost.
And then there is the Earth.
It hangs low over the northern horizon, about a hand’s breadth up from this particular ridge, and it is two degrees across, which is four times the width of the Moon from a garden on Earth — a thumbnail at arm’s length, not a dot. And it does not move.
That is the thing. Everybody is told that the Earth does not rise or set from the Moon and everybody nods, and nobody understands it until they have lived under it for a month and watched it sit in precisely the same place over the same two peaks, through sleep and shift and sleep, never a degree higher, never a degree further along. It wobbles. Over the month the libration walks it in a slow small loop a few degrees across, so that if you photograph it at the same hour every day for a year you get a lopsided figure of eight, and that is the whole of its movement, and the eye cannot see it happening any more than it can see a clock’s hour hand.
It is blue, and it is bright. Full Earth on the lunar surface is some fifty times the light of a full Moon in a terrestrial field, and it is enough to walk by, to work by, to read a large label by, and it comes out of the sky as a soft blue-white that lands on grey dust and makes it the colour of ash with ink in it. Nothing on Earth is lit that way. In Earthlight, at the lunar south pole, everything has a faint cold blueness and a double shadow, one from the Sun and one from the Earth, and the two shadows go in different directions and are different colours, and that detail alone had cost Caio about an hour of his first week.
It goes through phases, opposite to the Moon’s, so the night side of a lunar month is lit by a full Earth and the sunlit part of the month has a thin Earth-crescent hanging in the black. And it turns. It is the only thing in the lunar sky that does anything at all, and what it does is revolve, once a day, so that you can stand outside at the end of a shift and watch Africa come round the edge, and the Atlantic after it, and the weather moving — actual weather, white fronts curled up in the blue, visibly crawling if you give it an hour — and then the terminator sliding across, and all of it in complete silence, in a place where there is no weather, has been no weather, and will be no weather, ever.
Caio watched it for about four minutes, which was three minutes and forty seconds longer than the schedule allowed, and then went and did his pre-flight.
⁂
Caio Bettencourt was forty-one, was the only qualified pilot at Rim Nine, had not flown anything in eight months, and had been dreading one specific conversation since 04:12.
Seven years earlier, on a crewed approach to a station node that everyone involved now discusses with great vagueness, the sequencer had called a hold at forty metres, and Caio had looked at the closure rate and the plume geometry and had overridden it and completed the approach by hand, and had been right. The node had a soft seal failure that the hold would have turned into a slow collision over about twelve minutes, and his deviation is the reason two people are alive.
The board had been complimentary. The agency had put him in a photograph.
What nobody in the photograph knew was that he had not worked out the seal failure. Something in his hands had disliked the hold and had moved before he had a reason, and the reason had been handed to him afterwards by a board of inquiry as though it had been his all along, and he had taken it, because what else do you do.
Since then he had been the most procedurally exact pilot in the service. His simulator scores were the kind they show to visitors. He had not deviated from a written sequence by so much as a second in seven years, and he knew precisely what that was, and so did his wife, who had told him so twice, kindly, before deciding that twice was enough.
Thanh came and found him in the workshop on the second evening, under the sign.
— I need you to fly.
— I know.
— I need you to fly it the way the dynamics say and not the way it looks.
— That’s the only way I fly anything now, said Caio.
Thanh looked at him for about a second longer than the sentence required.
— That wasn’t a compliment, she said, and it wasn’t an instruction. It was the start of something I’ll come back to. Go and talk to Imane. She’s been waiting for you with a face on.
⁂
Imane had been waiting for him with a face on.
— Right, she said, before he had his helmet off the rack properly. Three problems, worst last, and I want you to tell me which one you’d have guessed.
— Where it is.
— Oh good, you’re not going to be a pilot about this, said Imane. Yes. Nobody knows where it is.
She had the fit up on the screen: four days of tracking, a cloud of residuals, a confidence ellipse that was a hair’s breadth across in two dimensions and enormous in the third.
— We know its orbit beautifully. Altitude, inclination, the shape, the plane, all of it, to metres. What we cannot tell you is where it will be on that orbit on Thursday, because that depends on the period, and a one-second error in a two-hour period puts you fifteen hundred metres out per lap, and by Thursday it has gone round forty-eight times and you are seventy kilometres out, and still spreading, and no amount of staring at it harder helps.
— The Moon’s lumpy, said Caio.
— The Moon is catastrophically lumpy, and the Moon is not my problem. The Moon is mapped. My problem is that your lander is leaking.
She put up the light curve. A tumble, period forty-four seconds, and a residual acceleration on the orbit that nothing in the model would own.
— There’s a cracked line somewhere on a water tank, said Imane. It vents, it flashes, half of it freezes, and the whole thing acts as the world’s worst thruster, pointing wherever the tumble happens to be pointing at the time. The mass loss is nothing, it’s grams a minute, it would take four centuries to empty at that rate. The push is what matters. It’s a ten-millionth of a gravity and over four days it moves the thing tens of kilometres and I cannot predict it, and neither could anyone, because it depends on a tank temperature I can’t see and a crack I can’t imagine.
— So we measure it every pass.
— We measure it every pass, we get a good answer six hours out and a useless one four days out, and the last correction gets made as late as physics allows by a man looking at the thing with his own eyes. That is problem one. Problem two is the window.
Caio had already done problem two in his head and had been hoping to be wrong about it.
A vehicle leaving the surface arrives in a plane that contains the launch site. Kittiwake’s plane was fixed in space; the Moon turned under it, carrying Rim Nine round once in twenty-seven days; twice in that period the base passed beneath the plane, and at those two instants, and no others, you could take off and be in the right plane without paying.
Paying meant a plane change, and a plane change is the most expensive routine thing anybody does in space. Swinging a hundred-kilometre lunar orbit by ten degrees costs roughly what it costs to launch off the surface in the first place. The hopper had never been built to own that kind of margin. It was a taxi.
Imane put the pass times up.
— Next alignment: nine days and fourteen hours.
— And our margin is fourteen.
— And your flight is two to three days if nothing goes wrong.
— And problem three.
— Problem three, said Imane, with the particular relish of a woman arriving at her subject, is that when you get up there it will be a hundred and forty degrees ahead of you in the same orbit, and every instinct you own will be wrong.
⁂
She made him sit through it anyway, with a pencil, which he did not resent as much as he pretended.
— It’s ahead of you. What do you do?
— Burn prograde, said Caio obediently. And then I fall behind.
— Say why.
— Because thrusting forward doesn’t make me faster, it makes my orbit bigger. Bigger orbit, longer period. I go round slower. The faster I push the further behind I drop.
— And to catch it?
— I brake. Drop into a lower orbit, shorter period, go round quicker, come up underneath it from behind, having never once pointed the engine at the thing I’m chasing.
— And the resource you spend?
— Time. Not fuel. Time.
— Good, said Imane. Now the important part, which is that none of that will help you at all.
— Thanks.
— I mean it. I have taught this to four crews. Every one of them nodded exactly like you nodded. And every one of them, in the box, with the target in the window getting further away, reached for the stick, because there is something in the middle of a human being that cannot be taught this. You can know it with the whole of your education and your forearms will still try to throw a rope.
Oskar, from the doorway, in the hat, said it was like beating upwind.
— It is not like beating upwind, said Imane.
— It is a bit like beating upwind.
— It is like beating upwind if going faster made the wind go backwards and the harbour move, said Imane, and Oskar said fine, and left, and the standard of argument improved.
There were two ways to do the chase and they failed differently, which is the most useful property two options can have.
Patient: drop a long way down into a phasing orbit, go round several times quicker than the target, let the angle close itself, come back up alongside having spent almost nothing. Cost: two days, and a periapsis down at twenty-two kilometres over the lumpy nearside, which is a place where nobody sane spends two days.
Impatient: buy the angle with a hard burn and stop it with another. Cost: time, almost none; propellant, nearly all of it. Imane’s numbers came out at a four percent reserve on return, which is not a reserve, it is a rounding error in a reserve’s coat.
— Slow and low, or fast and dry, said Thanh. Both get worked all the way to the end before anybody has a preference. I notice we all have one already and we have no data, which is how crews die.
⁂
What changed the week was Imane doing the dullest possible thing sixteen times.
Every two hours Kittiwake came over and Rim Nine ranged it and tracked it and fed the numbers into the fit. Position: hopeless at four days. But the plane — the orientation of the orbit in space — came out gorgeously, because a plane is a slow and stately thing that a dripping tap cannot shift.
And the plane was moving faster than the planners had assumed.
Planes do move. The lumpy field makes them precess, and the rate depends on altitude and inclination, and the model handles it perfectly — using the orbit the vehicle was supposed to be in. Kittiwake was not in that orbit. It had fired for nine seconds before quitting, which had pulled its low point down a long way, and the precession rate had changed with it.
It was swinging toward Rim Nine.
Imane came into the galley at one in the morning base time and did not sit down.
— The window isn’t in nine days. It’s in thirty-one hours.
Four people did the same arithmetic in parallel and nobody said anything for a while.
— Imane, said Oskar carefully, from under the hat. Is there any chance you’re wrong?
— Every chance. The entire reason we’re in this mess is that nobody can predict anything about that vehicle. What there is no chance of is finding out by waiting. If I’m right and we wait, we’re dead in fourteen days. If I’m wrong and we launch, we burn the hopper’s margin on a plane change we can’t afford and we’re dead sooner.
— And the thing that decides it, said Caio, from the doorway, is the same lumpy gravity that lost it for us in the first place.
— Yes.
— The thing that took it is handing it back.
— If I have the sign right, said Imane. And I would like three people to check the sign, because I have been awake for nineteen hours and a sign is precisely what a person gets wrong at the end of nineteen hours.
They checked the sign. Oskar checked it. Thanh, who had not done orbital dynamics since her qualification and said so twice, checked it anyway on the grounds that a wrong sign is usually obvious to a stranger. The sign was right. Four people stood round a screen at two in the morning under a Sun that had not perceptibly moved in a week, agreeing about a number.
— Thirty-one hours, said Thanh. Fly the patient one. I want the propellant in the tanks and not in the schedule. Oskar, what’s the quarry at?
— Nine kilos yesterday. The hammer is definitely making the noise.
— Then make it twelve somehow and don’t break your wrist, because our pilot is going to be busy.
⁂
The hopper was called Tern, because the agency names landers after seabirds, which Oskar held to be the single most ridiculous convention in spaceflight.
— Kittiwake. Tern. There is a Petrel at the equatorial site and a Shearwater on the manifest for next year, he had said, more than once. Every one of them named for a bird that eats fish. There are no fish. There has never been a fish. In four billion years this entire body has not had so much as an unkind word about a fish.
— What would you call them?
— Numbers, said Oskar. I would call them numbers and I would be happy.
Launching from the Moon has almost no theatre in it, which is the first thing that surprises anybody who has done it on Earth.
No roar — there is nothing to carry a roar, and what Caio heard was the pumps and a hiss that was his own suit and a deep structural note through the couch like a door closing in a large empty building. No shaking. No atmosphere to punch, so no profile built around not being torn apart, no maximum dynamic pressure, nothing to fight. Two thirds of a gravity in the back, politely, for seven minutes.
And he did not climb. That is the other thing. Tern tipped over almost at once and spent the whole burn going sideways, because getting into orbit has never been about height; it is about going fast enough sideways that you keep missing the ground, and height is only the part that gets you clear of the scenery.
He watched the scenery go.
Dust left the pad radially in every direction at a speed that looked wrong, flat and fast and silent, and did not settle, because there was nothing for it to settle through; it simply went, over the horizon, gone. The ridge dropped away with its clock-hand shadows. The permanently shadowed floor beside it, from four kilometres up, did not look like a dark place. It looked like an absence, a piece cut out of the Moon with scissors, and somewhere down inside the absence was a man in a hat, with a jackhammer, mining frost.
At seven minutes he was in orbit, a hundred and four kilometres up, with Kittiwake a hundred and thirty-eight degrees ahead and no way to reach it except to deliberately fall behind.
— Rim Nine, Tern. In plane.
— In plane, said Imane, and the plane is correct, in a voice with a great deal underneath it.
⁂
The chase took thirty-one hours. Here is what thirty-one hours is.
It is a coolant solenoid in the bulkhead behind his left shoulder that clicks every forty-one seconds. It clicked for the first hour without his noticing. In the second hour he noticed it. In the fourth hour he knew its rhythm well enough to feel the click arriving before it came, and by the ninth hour he had counted eight hundred of them and had made himself stop, and had then caught himself at it again twenty minutes later.
It is a cabin that goes cold on the night side. Tern is a small pressurised can with thin walls and a radiator that does not care about his comfort, and on the far side of the Moon the wall beside his knee cooled until he could feel it through the suit layer, and frost grew on the inner surface of the window at the corners in a fern pattern, from the humidity of one man breathing, and he had to scrape it with a gloved thumb and watch the scrape fog over again in six minutes.
It is the smell. The scrubber canister puts out a faint sharp mineral smell that everyone calls lithium and nobody has ever confirmed, and under that is hot electronics, and under that is a man who has been in a suit for a day.
It is the terminator. The hopper crosses from day into night in about four seconds, and the night on the far side with the Earth below the horizon is a blackness that has no equivalent in human experience: the window stops being a window and becomes a mirror, and what is in the mirror is a tired man’s face lit green from an instrument panel, four hundred kilometres above a surface he cannot see and is moving across at sixteen hundred metres a second.
And it is the ground, which was the part he had not been ready for.
At a hundred kilometres the Moon is a map. At twenty-two it is not. He dropped into the phasing orbit at the end of the second hour, the retrograde burn pulling him down over the next half-lap, and when he looked out at the low point the surface directly beneath him was crossing the window at four degrees a second, which is the speed of the second hand of a clock, except that the second hand is a mountain.
There is no air to go soft with distance, so nothing fades. A crater rim thirty kilometres away is exactly as sharp as the rail two feet from his hand, and his eyes kept trying to put the rim at arm’s reach and his inner ear kept agreeing with them, and the result, the first three times, was a lurch in the stomach of the kind you get on a stair that has one more step than you counted. He was in free fall and his body kept insisting he was falling, which was correct, and kept proposing that he do something about it, which was not.
Over Mare Nubium the ground came up at him. That is what it looked like. The lumpy field was pulling his low point about and the altimeter wandered by two kilometres over a few minutes, and the mascons under the basins reached up and took hold of the vehicle and let it go again, and the readout counted down in a leisurely way toward a number that it was not going to reach and that he watched anyway, with his jaw tight, for forty minutes, because it is one thing to have read the word perturbation and another to be inside it.
Twenty laps. Seven degrees of angle closed per lap. Two sleeps, neither of them good, strapped to a wall in a seat that had been designed by somebody who had clearly slept in a bed every night of his life.
On the ninth lap he caught his right hand on the translation controller.
He had not decided to put it there. It had gone there while he was looking at something else, and he found it resting on the grip with the forearm already tensed, in the attitude of a man about to give a shove to something that was a hundred kilometres ahead of him and getting further away in angle every minute exactly as the plan required.
He took the hand off. He looked at it for a while. Then he said out loud, in a vehicle where nobody could hear him:
— If it feels right you’re already in the wrong orbit.
And then he sat on both hands for twenty minutes, which is in no procedure anywhere, and which may have been the single best thing he did on the entire flight.
⁂
It came up out of the dark at him on the twenty-first lap, and the last hour was the first hour that felt like flying.
At nine kilometres it was a bright irregular star with a flicker. At two it was a vehicle: four tonnes of structure, legs still folded, one radiator panel bent over at an angle that explained a lot, and a thin white feather coming off the port side of the service section, eight or nine metres long, absolutely straight, visible only where it caught the Sun — water flashing out of a cracked line, half of it vapour and half of it ice crystals, and the ice crystals catching the light like a struck match held sideways.
— Rim Nine, Tern. I have the leak and it’s exactly where you said. It’s beautiful and I hate it.
— How’s the tumble?
This was the question, and the answer was the first piece of luck of the entire fortnight, except that it was not luck, it was physics being dependable.
Kittiwake was not tumbling any more. It was spinning flatly and steadily about one axis, at a bit under one and a half turns a minute, with that axis lying almost exactly perpendicular to the orbit plane and holding there.
Nothing is perfectly rigid. Propellant sloshes, structure flexes by microns, and every flex turns a little rotational energy into heat and throws it overboard, while angular momentum stays exactly where it was. The lowest-energy way to carry a given angular momentum is a flat spin about the axis of greatest inertia, so anything left alone long enough will dissipate itself into that state and sit in it. It embarrassed the first American satellite in 1958 and it has been quietly happening to unattended hardware ever since, and it had happened to Kittiwake, which had spent nineteen days sorting out its own affairs.
Which meant it had poles. And a point on the spin axis goes nowhere: the structure turns around it, and the point itself is still.
— Stable flat spin, one point four rpm, axis normal to the plane, said Caio. The forward collar is three metres off the axis. I’m going in down the pole.
— Tern, confirm you are not matching rates.
— Negative on matching rates. Matching a one-four body with this vehicle costs propellant I need to get home and it puts me inside the swept volume for four minutes. Down the pole, the collar makes a circle three metres across every forty-three seconds, and I put the arm into that circle at the near point and let the structure bring itself to me.
A pause of exactly the right length, and then Thanh’s voice rather than Imane’s.
— Is that the procedure?
— No.
— Is it in any procedure?
— The procedure for a spinning target assumes a cooperative vehicle that can be commanded to despin. Mine can’t be commanded to do anything. The procedure’s next line is abandon approach and I can read you the paragraph.
— Why is your way better.
And he heard the question properly — heard that she had been building toward it since the second evening, and that she was not asking whether he could do it.
— Because matching rates is four minutes inside a rotating structure with an eight-metre radius, with my attitude control fighting a rate nobody wrote the software for, said Caio. The axis approach is twenty seconds of exposure at contact. The thing I’m actually worried about is angular momentum transfer at grapple, and I can predict that, because I know its spin rate and I can get its inertia from the mass properties in the cargo manifest to about fifteen percent. I’d like Imane to run it. If the transfer puts a rate on the stack I can’t null with what’s left after the return burn, I abandon, and I’d rather take that call now than argue about it at three metres.
Another pause.
— Imane says run it, said Thanh. Imane also says that is the first time in her career anybody in a vehicle has asked her a question instead of telling her an answer.
Four minutes later the number came back. Capture at the near point, arm compliant, thrusters inhibited: two thirds of a degree per second on the combined stack. Inside Tern’s authority with margin, provided he was not simultaneously fighting a translation error.
— Tern, one more thing and then I’ll be quiet, said Thanh. Seven years ago you did the right thing for a reason you didn’t have yet, and you have spent the time since punishing a man who saved two people, and from out here it has been extremely boring to watch. What you just did on the loop is the same act with the reason attached. Please notice that you did it. That’s all. Go and get the water.
⁂
The approach took fifty minutes and the last three metres took fourteen of them.
Down the axis, the whole vehicle turned in front of him like a slow terrible flower. The structure swept through the edges of his vision — a leg, the bent radiator, the leg again — while the point he was aiming at did not move at all, and the disagreement between the centre of his sight and the edges of it was an insult his body would not accept. Twice his hand wanted to pull back and both times he let it want and kept his closure at four centimetres a second, which is roughly the speed of the minute hand on a large clock, and twice he had to deliberately unclench his jaw because his teeth had begun to ache.
The collar came round. Forty-three seconds. Came round again. He let three full turns go by doing nothing at all, which cost nothing and gave him the period to a tenth of a second, and on the fourth he put the arm out.
Contact was a bang.
Not a clang: a bang, a single hard event that came up through the arm and the frame and into the couch and through the couch into his spine, and then the world began to turn and did not ask.
Four tonnes of spinning structure had just been introduced to two tonnes of stationary one, and the angular momentum went where it had to go, in about a third of a second. The stack yawed. The couch came round and pressed him diagonally, left shoulder and right hip, a sensation with no name and nothing like a clean acceleration, more like being leaned on by a building. The panel gauges did not move, because gauges do not move, but his eyes moved, and the whole instrument face swam for a second and a half while his inner ear sent urgent and completely false reports about which way was down. Somewhere in the structure a longeron rang like a dropped bar. The reaction wheels came up in pitch, from a hum he had stopped hearing hours ago to a thin rising howl, and saturated, and quit.
Then the master alarm.
It is a loud, stupid, two-tone noise invented by somebody who has never been frightened, and it filled the cabin, and with it came the attitude warning and the rate warning and the star tracker dropping lock and the caution panel lighting up like a fairground, and underneath all of it, instantly and without consulting anybody, the automatic control system began doing its job, which was to null the rate, which it proposed to do with the forward thruster quads.
The forward quads pointed at Kittiwake’s port service bay.
Four metres away. Where a cracked line was venting a straight white feather of water into vacuum.
He had been looking at that feather for fifty minutes.
There is no version of this in which he worked it out. He has been asked, and he has stopped giving the modest answer, because the modest answer is a lie in the other direction. What happened is that his left hand went to the thruster inhibit and his mouth said no to a machine that could not hear him, and the hand got there in about a second and a quarter, and the first forward pulse had already fired — he felt it, a bang-bang-bang through the frame like someone kicking a tank — and the second one did not.
Then he sat in a rotating vehicle with the alarm going and did nothing for ninety-one seconds while the stack turned, unopposed, two thirds of a degree a second, because the alternative was a hot exhaust plume into a leaking bay at four metres, and ninety-one seconds is a very long time when the only thing you are doing is declining to act.
The alarm went on the whole time. He could have silenced it. He left it, because the hand that silences an alarm is the hand that goes on to do something else, and he did not want that hand available.
At thirty seconds the rotation brought Tern’s nose round into the feather.
He saw it coming and could do nothing about it, and for seven seconds the plume played across his forward window, and the water hit cold glass and did what water does when it hits cold glass in vacuum, which is that it does not run, does not bead, does not drip. It arrived as ice. A white bloom came across the window from the lower left like breath on a mirror and stopped being transparent, and did not clear, and was never going to clear, and that was that.
— Tern, Rim Nine, we have your rates, what is your status, said Thanh, in the voice she kept for this.
— Rates are as predicted, forward quads inhibited, I’m nulling off the aft set, said Caio. It’ll take longer and cost more. Also I’ve been snowed on.
— Say again.
— The leak got my window. I have about forty percent of it glazed and I’m not going to get it back.
A pause.
— Can you fly home like that?
— I can fly home like that, said Caio. I came four hundred kilometres to get rained on, and I would like that written down somewhere permanent.
It took four minutes on the aft quads, in deliberate small pulses, with the stack swinging past the Sun every forty-odd seconds so that the frosted half of his window went from grey to blazing white and back and made him flinch each time. When the rates were nulled he sat for a moment with sixteen tonnes of water on a stick and his hands shaking in a way that he noted with some interest and decided not to mention.
— Stack stable, said Caio. And I’d like to log a deviation.
— Logged.
— I want the reason in the same entry, not after. The reason is the plume geometry on the port bay. I saw that feather at fifty minutes out. I should have inhibited the forward quads before contact and I didn’t, and that’s mine, and next time I will.
— That is not how most people write those, said Thanh.
— I know exactly how most people write those, said Caio.
⁂
A board sat for six weeks and concluded that the thermal flux from the forward quads at four metres would probably not have ignited a water plume, there being nothing in a water plume to ignite — and then spent nine pages on what it would have done to the structure, the bay insulation and the cracked line itself, and used the word probably in a load-bearing way, and recommended a software change that ought to have been made fifteen years earlier.
Oskar’s considered opinion, delivered in the galley in the hat:
— They have now written nine pages about a man who did nothing for ninety-one seconds. This is the correct use of a board.
⁂
He brought it down thirty-one hours later and the descent was unremarkable, because by then the hard part had been over for a day and the rest was arithmetic that three other people had checked. He flew the final approach looking through the clear forty percent of his window with his head tipped to the left like a man reading a newspaper over somebody’s shoulder, and put it on the pad four metres off centre, which Oskar has never allowed him to forget.
The tanks came off Kittiwake in the shadow of the ridge over the following week. It was Oskar’s finest hour and he conducted it like a surgeon and narrated it like a man selling a car.
Rim Nine washed on the fourteenth day, and that needs describing, because a shower in a sixth of a gravity is not the thing the word suggests and nobody had warned any of them either.
It is a cylinder with a door, a low-pressure head at shoulder height, a downdraft fan, a squeegee on a hook, a drain with a filter and a suction pump under it, and a timer. Four minutes. Nine litres. The timer is not negotiable and the fan is not optional and everybody hates the fan.
The first thing is that the water comes down slowly and you can watch it do it. From the head to the floor is about a second and a half, which is long enough to follow a drop with your eye, and the stream separates on the way into a loose column of fat lazy beads. It does not drum. An Earth shower hammers on the top of the skull, which is most of what people actually mean by the word; this arrives at a walking pace and lands on you the way a hand lands on you, and the first time, Oskar said afterwards, he stood there waiting for it to start properly.
The second thing is that it will not come off.
Water on skin is held by surface tension and taken away by weight, and at a sixth of a gravity the weight has mostly gone and the surface tension has not changed at all, so everything you know about how wet works is wrong by a factor of two and a half. A drop can be two and a half times bigger here before it slumps and runs. A film that would have sheeted off your forearm in a second instead sits there as a thick trembling lens, moving when you move, going nowhere. You do not get rinsed. You get upholstered. You come out of the water carrying about twice as much of it as you would on Earth, and you have to take it off yourself, by hand, with a rubber blade, which is why the most important tool at Rim Nine after the jackhammer is a windscreen wiper.
Soap is worse and much funnier. Lather drains under its own weight, so at a sixth of a gravity it does not drain; it stands. A handful of foam becomes an architectural event. It rises, it holds its shape, it leans. Oskar came out of his first wash on the fourteenth day with his hair in a single standing white column about twenty centimetres high, perfectly stable, and walked the length of the habitat with it before anybody told him, and Imane has the photograph and has made certain it will outlive them all.
The air is the part that surprises people who have thought about the water. Warm wet air gets out of your way on Earth because it is buoyant and rises, and buoyancy is a gravity effect, so here it barely bothers. Your own warm cloud stays on you. Without the fan the cylinder fills with a hanging fog inside forty seconds and you stand in a personal swamp of your own making and breathe it, and the fine spray thrown up off the floor goes high and slow and takes its time coming back, drifting, in a way that is genuinely lovely to watch and absolutely has to be pulled down into the drain, which is what the fan is for, and which is why nobody gets to switch it off no matter how loud it is at four in the morning.
Oskar went first, by unanimous agreement and without a vote, on the grounds that he had spent twelve days in a hole at forty kelvin and the rest of them had not.
For the first ten seconds the water that went down the drain was black. Not grey: black, with the particular flat non-reflecting blackness of lunar fines, which get into the weave of everything and into the creases of your hands and into the skin itself, and which no glove seal has ever entirely defeated. The filter came out afterwards looking like something from an engine and Thanh photographed it for the maintenance log and then, separately, for herself.
He was in there for his four minutes and he did not say anything at all for the last two of them, which from Oskar was remarkable, and he came out looking about ten years younger and said only:
— Right.
Then he went and sat down and put the hat on.
Caio went last, as the pilot, because flying was still three days away and he wanted the smell of the suit out of his sleep. He used three minutes and forty of his four minutes on being clean and the final twenty standing still underneath it with his eyes shut, doing nothing, while beads of water the size of grapes assembled on his shoulders and declined to fall.
On Earth a shower is the thing you do to stop being dirty, and it is over when you are clean, and nobody thinks about it again. At Rim Nine it is the only occasion on which any of them was ever touched by something that was not a machine, a seam, a glove, or the inside of a helmet.
Thanh had declared it a formal occasion. Everybody made jokes about it beforehand and nobody made any afterwards.
The quarry was shut down on the sixteenth day, by which time it had produced two hundred and six kilograms of water by hand, which is a figure Oskar can still give to the gram, and which, at the rate the plant now does it, takes the plant about forty minutes.
— And I would do it again, he said.
— You would not.
— I would do it again, said Oskar, and I would complain in exactly the same way, and that is the whole of what a job is.
⁂
About a month afterwards, in the slow part of a lunar night, Caio sat down to write to his wife.
There is a desk in the second cylinder which is a shelf, and above the shelf is a small thick window, and in the window, where it always is and where it does not move, was the Earth: low over the northern horizon, a third lit, blue and white and very small, with the terminator across it. It does not rise and it does not set. It wobbles a little over the month, a few degrees of libration, like a face moving in sleep, and that is all it does, for ever.
He wrote it out longhand first, on actual paper, with an actual pencil, because a pencil on the Moon works properly and he liked that about it. In a sixth of a gravity the pencil wants to skate: there is not enough of your hand’s weight to settle it, and the line comes out light and the letters come out larger than you meant, so his handwriting on the Moon had become the handwriting of a much younger and more confident man, which he had noticed before and had not previously had any use for.
He wrote: I have got back in touch with myself.
He looked at it for some time. Then he scratched it out, hard, four or five strokes, and the pencil skated on the last one and went off the edge of the paper and left a grey scar on the shelf which is still there.
Because it was the kind of sentence that sounds better than it is, and because it was not what had happened.
What had happened was smaller and more useful. He had spent seven years trying to find, inside his own head, the moment of the decision at the node — the gap where a choice should have been sitting — and he had never found it, and had concluded from the absence that there had been no decision, only luck in the costume of judgement. And then he had spent thirty-one hours in a cold can with a clicking valve, and had wanted to push the stick and had not, and had said a reason out loud on an open loop to a woman who checked it in four minutes and told him he was right, and at no point in any of that had he experienced a gap either.
The difference between a hunch and a reason is not available by introspection. You cannot get at it by looking inward, which is what he had been doing, alone, in the dark, with the shutters shut and no witnesses, for the better part of a decade. The difference is simply that one of them can be said before the event and checked by somebody else.
That is all. It is a procedural distinction, not a spiritual one, and it is available to anybody willing to say the reason out loud on the loop first instead of to a board afterwards.
He wrote instead: I have started flying again, and I am talking more at work, which you would find funny.
Which was the same information, and was true, and fitted on one line.
⁂
One last thing, for people who like the small ones.
When the tanks were off and the carcass of Kittiwake was no longer any use to anybody, the tidy disposal was to put it into the Moon at a surveyed point, which is a strange errand to be given. It went in north of the base at sixteen hundred metres a second, and from the rim they watched the plume go up for about ninety seconds — slow, silent, white, in a vacuum that let it rise far higher than anything that size has any business rising — and then not rise, and then settle, and then stop. And there was a new crater on the Moon, perhaps thirty metres across, in a place where nothing had happened for a very long time and nothing would happen again.
Imane had the coordinates and had put them on the board, and Oskar, in the hat, asked why.
— Because now it has an address, said Imane.
The Other Face
It came out of the core tube at forty-one centimetres, and the first thing Nadia Shenouda thought was that somebody had dropped a washer.
That is not hindsight and it is not modesty. Her lamp was on it, the crater floor was at sixty kelvin and had not been touched by sunlight since before anything on Earth had a backbone, and the object lying in the split half of the tube was a flat grey disc the width of a bottle cap, and the thought that arrived, whole, in the head of a woman with nineteen years in the field, was: somebody has dropped a washer in my hole.
— Lóránt.
— Mm.
— Did you drop anything.
— I have not dropped anything in four years, said Lóránt Bakos, from the rover, in the voice of a man who had been waiting a long time for somebody to accuse him. What have you got?
— I don’t know yet.
— That is not an answer a person gives.
— It is the only one I have, said Nadia, and then put both wrists down on the regolith and left them there until they stopped shaking, because she was damned if she was going to be the woman who dropped it.
⁂
Mercury’s poles are the attic of the inner solar system and nobody gives them the respect they are owed.
The planet has effectively no axial tilt — two hundredths of a degree, which is to say none — so the floors of its polar craters have never, in the whole history of the solar system, had sunlight on them. Not briefly. Not seasonally. Never. With no atmosphere to carry heat sideways, those floors sit between fifty and a hundred kelvin, a few hundred kilometres from ground that reaches seven hundred at noon.
Which means they catch things and keep them.
Water goes in and stays. The radar-bright patches have been known since the nineties, and the ice under its dark lid since the orbiter work, and everything else that arrives stays too, because there is no weather, no flow, no wind, no chemistry worth the name, and nothing to shift anything except the slow rain of micrometeorites that stirs the top few centimetres and leaves what is underneath alone.
— It is a drawer, Nadia told every incoming rotation, for four years. The coldest drawer in the inner solar system. It has been standing open the entire time and nobody has ever gone through it.
And the second half of the sentence, which she said less often:
— Drawers are not full of messages. Drawers are full of what fell in.
⁂
The rover was called Linden, because the committee that names things for the Mercury programme had decided, at some point, to name the surface vehicles after shade trees.
Nobody has ever established whether this was a joke.
— Banyan. Plane. Linden, said Lóránt, roughly weekly. On the planet where shade is the only thing that matters and there is none of it except the piece you are standing in, which you will lose in four hours.
— You love it.
— I adore it, said Lóránt. It is the most considered act in the agency’s history and I refuse to believe anybody meant it.
The traverse rule fits on one line and everything else is a consequence: you live in the shadow, and the shadow moves at walking pace.
Mercury turns once in fifty-nine days and goes round the Sun in eighty-eight, locked three-to-two, and those two numbers give a solar day of a hundred and seventy-six. The line between day and night crawls across the equator at three and a half kilometres an hour. You can outwalk the dawn. People do it for fun on training rotations, and then they do it for work, and it stops being funny about the second time the schedule slips.
And the thing that kills you is not the Sun.
— Say it, Lóránt asked every new arrival at the airlock before they went anywhere.
— Shade isn’t safe.
— Why not?
— Because the wall opposite me can be in sunlight, and the wall is at four hundred degrees, and it radiates in a straight line, and it does not care that I am standing in a shadow.
— And that does what?
— Cooks one side of me while the other freezes.
— Good. Say it again in a month when you have got lazy.
No simulator prepares anybody for this. On a world with air, the air smears heat about and softens everything. Here there is nothing to smear anything, so the environment is not an environment, it is a collection of surfaces, each at its own temperature, each throwing infrared at you across vacuum with no falloff worth mentioning. Standing in a boulder’s shade with a sunlit scarp four hundred metres off is standing in front of an open furnace with a postcard between you and it. The shadow is the postcard. The postcard does not reach the scarp.
Nadia’s party trick for visitors, in the safe zone where a ridge lays a hard permanent edge across the ground: stand with the line between your boots, put one glove in the light and one in the dark. A hundred and ninety above zero on one hand. A hundred and sixty below on the other. The difference happens across the width of a pencil, because there is no air to argue about it.
— That is the whole planet, she would say. One line, two worlds, no transition. Never stand with a foot in each.
⁂
The disc went straight into a cold vessel, and this is the part that matters, and at the time it was simply procedure.
The sample vessel is a passively cooled dewar: a gold-shielded flask with a radiator cap, which in the permanent shadow of a polar crater sits at the temperature of its surroundings and holds there for as long as it can see cold sky. There is no power in it. It is a thermos with ambitions.
You do that because of the film.
Anything lying in a cold trap for four billion years does not lie there clean. Volatiles wander in — water, sulfur compounds, organics delivered by comets and by the solar wind working on the rock — and they stick to every cold surface they find, including the surfaces of whatever is lying there, and they build up, molecule by molecule, over geological time. The disc had a coating. Grey-brown, a few microns, visible under the scope as a dull bloom, the way a coin goes dull in a drawer.
— That’s not dirt, said Nadia, forty minutes later, in the rover, with the scope running and her gloves still on. That’s the only context this thing is ever going to have.
Lóránt had his hands behind his back, which is what he does instead of touching.
— Explain.
— One object, no stratigraphy, found in a layer that micrometeorites have been stirring for four billion years. We cannot say where it came from and we cannot say when it arrived. The film is different. The film accumulated while it was lying here. It is a clock and a logbook and it is four microns thick and it is held on by nothing but being cold.
— And if it gets warm.
— Then it is gas, said Nadia, — and gas in a vacuum is gone, and then we have a nice piece of metal with no history whatsoever, and I will have spent four years opening a drawer to find one object with everything scraped off it.
— At what temperature.
— The good stuff starts leaving around a hundred and fifty kelvin. By two hundred there is nothing left worth measuring.
— And the flask holds.
— The flask holds as long as it can see the sky, said Nadia. The flask cannot see the sky if there is a four-hundred-degree wall in the way.
Neither of them said anything for a moment, because they both heard it at the same time, and because it was not a problem yet.
⁂
It became a problem six days later, and before it did there was the scan, and the scan is where the floor gave way.
Nadia ran the film in the rover’s spectrometer on the fifth evening, because she was not going to wait eight months to find out what the coating was. It is a twenty-minute job and the answer is a set of peaks.
She ran the upper face.
Then she ran the lower face.
Then she sat very still and ran both again, swapping the order, because the only honest first thought is you have made a mistake with your samples.
— Lóránt.
— If this is about the chute I have already —
— Come here.
He came. She put the two traces up side by side, which anybody can read who has spent a week in the subject, and he read them, and she watched him read them, and she watched the moment he got there, because it is one of the three or four best things she has ever seen on a human face.
— They’re different.
— They’re different.
— They’re not a bit different, said Lóránt. They are a completely different inventory. That one is loaded. That one is practically bare.
— Say what that means.
— It means —
He stopped. He put his hands behind his back.
— It means one face was up for a very long time and one face was not, said Lóránt slowly, — and that is fine, that is what buried things do. And then it means that the bare face has some film on it, which it cannot have if it was buried the whole time, which means it has also been up. Which means both of them have been up.
— Which means.
— Which means it turned over, said Lóránt.
— Once. In four billion years. In a crater with no wind, no water, no atmosphere, no slope and no frost heave, said Nadia. Something turned it over.
Lóránt sat down on the edge of the bunk, which he did not normally do, and was quiet for about fifteen seconds.
— Right, he said. I am going to say a word once, in a small room, to one person, and then we are never saying it again on an open channel.
— Don’t.
— Artefact.
— Lóránt.
— That is how you handle that word, said Lóránt. You say it deliberately, in private, to somebody who will not panic, and then you put it away. If you do not, it waits until you are tired and comes out of your mouth on a loop that gets transcribed, and then it belongs to a press office.
— And what’s the sensible explanation.
— An impact. Something landed nearby, threw regolith, flipped it. Happens all the time.
— Yes, said Nadia.
— I’m going to keep saying that.
— Please do, said Nadia. Keep saying it for eight months. I need somebody to.
⁂
The exit problem arrived on the ninth day and it arrived because Mercury is shrinking.
The planet has been cooling for four and a half billion years and its interior has contracted, and the crust, with nowhere to go, has wrinkled into lobate scarps — thrust faults hundreds of kilometres long, some of them a couple of kilometres high. Some are young. Some are so young that the honest reading is that the planet is still at it, which means Mercury has quakes, which means a slope that has been stable since before the first cell on Earth can stop being stable in the time it takes to say so.
They heard nothing, because there is nothing to hear.
What they saw, coming back up the traverse, was that two hundred metres of their ramp was now lying at the bottom of it.
— Well, said Lóránt.
— How bad.
— Not bad at all if we had four days. We take the western chute. Wider, gentler, twenty minutes longer, and for about three hundred metres of it we are under the western wall.
— And the western wall is in sunlight in —
— Forty-one minutes.
They both looked at the number. Then they both looked at the flask, which was clipped in its cradle behind Nadia’s seat with a strip of frost on the collar where the cold was leaking into the cabin air, as it always did, as it was supposed to.
— Say the flask number, said Nadia.
— I don’t have a flask number. Nobody has a flask number. Nobody has ever driven a loaded cold vessel under a sunlit wall on this planet because nobody has ever been stupid enough.
— Then estimate it.
Lóránt did the arithmetic out loud, twice, because that is what you do.
— Rover’s twelve minutes. Flask is worse. It’s small, it’s got no power, and it is sitting inside a cabin that will be climbing. Under that wall, call it fourteen minutes before the inner vessel goes through a hundred and fifty.
— And the drive is twenty.
— The drive is twenty.
⁂
What follows took nineteen minutes and is the reason both of them are in the training material.
They went.
Linden is not fast. Linden is a seven-tonne pressurised box on six wheels designed by people whose central concern was that it should never, under any circumstances, tip over, and it goes down a chute at the speed of a determined pensioner. Lóránt drove it at that speed for eight minutes with his jaw set, and then the left forward hub picked up a rock the size of a thumb between the wheel and the fender and the drive cut out.
On any other planet that is a thirty-second job with a glove.
It is a thirty-second job with a glove here too. The thirty seconds come with six minutes of suit checks and egress either side.
— Out, said Nadia, already moving.
— Nadia.
— Out, out, out.
She did it in four minutes forty, which remains the fastest unscheduled egress in the programme and is now a line in a manual. She does not remember most of it. She remembers the seal check going green, and the hatch, and the ground, and the extraordinary clarity of the stars overhead, and the rock, which came out in her hand like a tooth, and the climb back in, and Lóránt saying go before the inner door had finished.
— Time.
— Ten minutes to do fourteen minutes of driving, said Lóránt, — and then we are under the wall, and then it lights.
— Flask.
— Seventy-one kelvin and climbing a degree every ninety seconds from the cabin alone. That’s fine. That’s nothing. It is what it does when it is in here. Under the wall it goes vertical.
The chute came past the windows. Grey. Grey. Grey. There is no colour on Mercury and no softness anywhere and nothing fades with distance, so the walls on either side were exactly as sharp at six hundred metres as the handrail by Nadia’s knee, and the whole thing came at them at a speed that any person who has ever driven anything would call a crawl.
— How long.
— Don’t ask me how long. Watch the flask.
— How long.
— Six minutes to the wall, said Lóránt. Nine minutes of driving after it. Fourteen on the flask. It does not fit. It does not fit by five minutes and I cannot drive faster, because if I put this vehicle on its side we will have a great deal more than five minutes to think about it.
Nadia had her hand flat on the cradle, which does nothing, which every person does.
— Options.
— Dump it out of the vessel and bury it in the floor, said Lóránt. Fifty centimetres of regolith, it stays cold, we come back for it in a hundred and seventy-six days when the geometry is good. We lose the flask, we keep the film.
— We lose the position. We lose the stratigraphy of the hole. We lose —
— I know what we lose. It is on the list, said Lóránt. It is the worst item on the list and it is still on the list.
— What else.
— We stop here and sit in the cold for nine days until the Sun clears the western wall, said Lóránt, — on four days of consumables.
— That is not on the list.
— No, said Lóránt. That is why I said it. The list is now complete, and I would like you to notice that both items on it are bad, and that I am going to drive at this speed either way.
And then the Sun came up over the ridge ahead of them, and stopped, and went backwards.
⁂
— Tamar, said Wen Jiaqi, from the station, into the loop, in a tone that made the station’s duty officer stand up. Tamar. Look at the west feed.
— I see it.
— It’s going backwards.
— I know what it is, said Tamar Kiknadze.
— The Sun is going backwards.
— Jiaqi, I know what it is, said Tamar, — and so do you, and so do they, and I want everybody on this loop to take one breath before anybody says anything they will hear played back at a hearing.
In the rover, Nadia was laughing, which is not an appropriate response and is a very common one.
— It’s the resonance.
— It is the resonance, said Lóránt, who had not taken his eyes off the chute and whose hands had not moved on the controls.
— We’re nine days from perihelion at a longitude of about a hundred and eighty. The planet’s going round the Sun faster than it’s turning. For a couple of days the Sun backs up, sets again, and rises a second time. It’s in the textbook. It’s in the planner, there is a column for it, it is four lines below the one I was looking at.
— How long does it give us?
Nadia pulled it up with hands that were not steady.
— Nineteen minutes.
— Then we are going to use fourteen of them, said Lóránt, — and this was a planning failure and that it was mine, and I would like that said now, while we are still frightened, because people get generous afterwards.
They came up out of the chute into the long cold shadow of the eastern rim with the flask at ninety-four kelvin and falling, and nobody said anything for about a minute and a half.
Then Wen said, from the station:
— I would like somebody to tell me that wasn’t a sign.
— It was two integers and an ellipse, said Nadia.
— I know.
— Kepler had the ellipse in 1609 and the resonance was nailed down in 1965 —
— I know, said Wen. I am not asking you to agree with me. I am asking you to give me forty seconds.
— Have the forty seconds, said Lóránt. Then help me write up a near-miss, because it is going in as a planning failure and not as an act of God, and the planning failure is mine, and if anybody tries to be kind about it in the report I will take it personally.
⁂
The film survived. That is the whole point of the chapter and it took eight months to pay off.
What was on the two faces, once four laboratories had it, was this.
The lower face carried a thick, layered, filthy accumulation: water ice, sulfur species, carbon compounds, and embedded in it, at the very bottom, a scatter of micron-scale particles that had arrived and been glued down and never moved. Those particles are old. Their crystal damage, their solar-flare track densities, their isotopes: they are debris from the era when the inner solar system was still being hit so hard and so often that the Moon’s face was being made, when the Earth had no continents to speak of and no life anybody could point at, and they have been lying on the underside of a disc in the dark at sixty kelvin ever since, undisturbed, while everything that has ever happened on Earth happened.
The upper face carried a thin, clean, much younger film, and implanted in its outermost few nanometres, the solar wind.
The solar wind leaves a dose. The dose on that face corresponds to an exposure of a few hundred million years — which is to say that the face now pointing at the sky has been pointing at the sky since roughly the time the Earth was growing coal forests and the first things with scales were deciding to lay eggs on dry land.
Four billion years on one side. Three hundred and forty million on the other.
And no air, no water, no slope, no wind, no frost, no process, no witness: a flat disc of iron in a hole in the dark, that lay one way up for four fifths of the age of the solar system, and then turned over, around the time of the first reptiles, and has lain the other way up ever since.
⁂
The committee wanted it to be an impact, and Nadia has never once held that against them, because so did she.
She has, however, kept the transcript.
Three sessions, seven reviewers, eight months, and the reason for all of it was a single sentence in section 4.3 which said that the exposure ages of the two faces differed by a factor of twelve and could not be reconciled by any shielding geometry.
They went at that sentence the way a committee should.
The first attempt was geometry. If the disc had been lying tilted, or partly buried, or shadowed by a boulder that is no longer there, could you shield one face enough to fake the difference? Three groups ran it. You can get a factor of two. With a boulder of an implausible size in an implausible place and a burial depth that contradicts the core log, you can reach three. The measurement is twelve.
The second attempt was the muons. The deep-penetrating component is modelled, and the models have parameters, and if you push the parameters you can move the ratio. One reviewer pushed them all the way to the edge of the published ranges and got to four and a half, and then, to his enormous credit, published the attempt and the failure, and the paper is still cited by people doing it properly.
The third attempt was the instrument, which is always the third attempt and is always right to be. They requested a blind recalibration, got it, got the same numbers, requested a second laboratory, got it, got the same numbers. The reviewer who had asked for it, a man named Pálsson who had been openly hostile in session one, said in session three: I have now spent four months trying to make this go away and I am obliged to report that I cannot, and I would like my previous remarks about Dr Shenouda’s methodology struck from the record, and I would like to buy her a drink.
And it was session three where the real argument happened, and it was not about aliens, and this is the part Nadia tells students.
A reviewer proposed that the paper state the impact-overturn explanation as the conclusion.
— It is the explanation, he said. It is overwhelmingly the most probable explanation. It requires no new physics, no new entities, nothing. And if we do not write it down as the conclusion, somebody else will write down something else, and we will have handed the subject to people who do not deserve it.
— All of that is true, said Nadia, — and I am still not going to do it.
— On what grounds?
— On the grounds that we did not observe it, said Nadia. There is no crater. There is no ejecta layer in the core. There is no second object. There is no mechanism in evidence. What we have is a very good argument from how often things get hit, applied to one object, with no independent confirmation of any kind, and if I put that in the conclusions I am not reporting a result, I am reporting my own prior, dressed up, in a journal, with my name on it.
— The alternative is to leave the field open to lunatics.
— The alternative is to leave the field open, said Nadia, — and yes, lunatics will come in, because the field is open, and they will write books, and one of them will be on television. And in thirty years somebody will find a second object with a context, and the thing that will save us then is that the 2061 paper said exactly what it measured and did not say one word more. That is the only protection any of us has ever had. It is not dignified and it does not play well and it is all there is.
The paper went out with the measurement, the natural explanation set out in full as the most probable account, and no conclusion.
Section 4.3 is four sentences long. Nadia wrote three of them. The committee wrote the fourth, which notes the impact hypothesis and says it is unverified, and which she regards, on balance, as an improvement.
⁂
Two more things, and then the drawer.
Wen Jiaqi spent the eight months conducting a campaign to have the object formally named, submitting, in order: Kiknadze’s Disc, which Tamar vetoed; the Shenouda Object, which Nadia vetoed with more force than was strictly collegial; the Mercury Flan, which the agency’s communications office rejected on the grounds that it sounded like a dessert; and finally Sample 2061-DK-04, which is what it is called, and which Wen submitted out of spite, and which she now insists was the plan all along.
The press ran with the Mercury Coin for three weeks anyway, which Nadia hated, and then the cycle moved on and it stopped being called anything, which she hated more and admits to in private.
And at the end of her last rotation, in the airlock, with the inner door cycling, Lóránt Bakos said:
— For the record. The chute. It was my error.
— It was the planner’s.
— It was mine, said Lóránt, — and I have been losing that argument on purpose for four years because it was the only reliable method I had for keeping you in a room.
Nadia looked at him for about the length of a suit check.
— I know, she said. Why do you suppose I kept arguing?
Then the door opened, because doors do, and they both went through it, and she caught the hop up to the station, and they write to each other most weeks, and that is where it stands and has stood for some time, and both of them appear to regard this as a satisfactory arrangement, which the two of them are entitled to do.
⁂
She went back to the site on her final traverse, which was not strictly authorised, and which Tamar approved with a single line reading: take the long route, the western chute is a planning failure.
She stood on a floor that has never been lit, and turned the lamp off, which you are not supposed to do.
With no lamp, no sunlight and no air, a crater floor on Mercury is not dark the way a room is dark. It is lit by starlight, which on an airless world is enough to see the ground by once your eyes stop expecting better, and the ground came up as a faint grey nothing, and the sky above it was absolutely full and did not twinkle anywhere, and low over the rim stood two steady lights brighter than anything else in it: Venus, which from Mercury is a lamp, and the Earth, which is a smaller lamp with a companion close enough that any eye can split the pair.
She had spent nineteen years opening other people’s drawers.
That is what the work is. You go to the coldest, stillest, least disturbed place you can reach, and you open it, and the entire time — under the method, under the error bars, under the professional language — you are hoping for a message. Everybody is. Nobody admits it on a transcribed loop. It is the reason anybody goes.
And what she had found, in the best-preserved drawer in the inner solar system, was a coin that somebody dropped, that lay heads up for four billion years, and then lay tails up for three hundred and forty million more, and that means nothing whatsoever, and is not a message, and is not addressed to anybody.
There is no malice in that and that is the part people get wrong. The universe is not hostile. It is not even uninterested, because uninterested would require a position. It is simply very large and very old, and in something that large and that old every sufficiently improbable thing happens somewhere, once, with no witness, and most of them are never found, and the one that is found gets a catalogue number and a sentence in section 4.3 and a woman who thinks about it on the bad nights for the rest of her life.
— Right, said Nadia Shenouda, out loud, to nobody, on a planet that cannot carry sound.
Then she put the lamp back on and went home.
Below Hearing
The thing arrived at 03:48, lasted a hundred and forty seconds, and was so quiet that the honest way to describe it is that the pressure in the room became very slightly interested in something.
Sarala Venkataraman was not asleep, which was not luck, because she had not been properly asleep at that hour of a Venusian passage for about four years.
She was in the lower bay with the lamps off and her feet up and a cup of tea going cold, watching three traces crawl across a screen at the speed of continental drift, and the middle one lifted.
Four millipascals.
For scale: a sheet of paper dropped flat on a table makes a louder noise than that, if there is anybody to hear it, which on the other side of the hull there is not and never will be. The lift took six seconds to develop, held, wobbled, came back down, did it again smaller, and a third time smaller still, and then the trace went back to being the trace.
Sarala put the tea down without looking at where she was putting it, which is how the cup ended up on the floor.
— Perpetua, this is Sarala. Everybody awake, envelope ballast locked, and nobody runs a pump, a fan, a centrifuge or a treadmill for four hours.
A pause of the kind that happens when two people are deciding whether to be annoyed.
— It is four in the morning, said Pilar Zepeda.
— I know exactly what time it is.
— You always know exactly what time it is, said Pilar. That is the entire problem with you. Another whisper?
— A whisper with a tail on it.
⁂
Here is what it is like to live in the one place in the solar system where you could, in principle, open a window.
Fifty-four kilometres above the surface of Venus the air outside is at about one atmosphere and twenty-seven degrees, which is a pleasant afternoon in most of the countries any of them came from. Gravity is nine tenths of Earth’s, so you walk, you do not float, you set a cup down and it stays down, and your spine ages at the correct rate. Cormac Dillane, arriving from a rotation where everything had to be velcroed, spent his first week putting objects on surfaces and leaving them there, apparently for pleasure.
Open the window and you would be dead four separate ways, in an order depending on which got there first. The air is ninety-six and a half percent carbon dioxide, which at a full bar puts you out in under a minute with none of the warnings your body is built to give. The cloud you are inside is sulfuric acid, not vapour but droplets, three quarters to ninety-eight percent concentration, which takes the lining off a lung and has opinions about metals. There is no oxygen worth the name. And all of it is moving: the whole atmosphere at this height goes round the planet at about ninety-five metres a second, a hurricane everywhere, always, which you cannot feel, because you are in it.
That is the part nobody gets used to.
Perpetua does not fly. Perpetua drifts, and the drift is the fastest thing on the planet, and from inside there is no sensation of motion at all — no sound, no buffet, nothing in the port but cloud going past at a speed you cannot judge because there is nothing to judge it against. The station laps Venus every four and a half days. The ground beneath turns once in two hundred and forty-three, backwards, so the surface is effectively standing still while the air goes round it fifty times faster, a fact the atmospheric people have been embarrassed about for a century because nobody has entirely explained it.
— I’ve read four explanations, said Cormac in his second week.
— There are seven, said Sarala. The first four are the ones that are wrong in interesting ways.
You cannot stop. No station-keeping, no hovering, no going back to look at anything. If you want to be somewhere you go up or down — the wind differs a little with height — and then you wait, sometimes a week, while the planet hands you the place you asked for. Everything Perpetua does, it does by changing altitude and being patient, which is either a philosophy or a sentence depending on the day.
The day, incidentally, is four and a half days long, because the station outruns the Sun. Two days of light, two of dark, and the light is not like light anywhere else: no sun in the sky, only a brightness arriving from every direction at once through a hundred kilometres of haze, the colour of the inside of an eyelid. There are no shadows. Nothing has an edge. From the observation port you see an unbroken floor of yellow-white going out to a horizon that is not a horizon but a gradual giving-up, and in all that time Sarala had never once seen the surface of the planet she was studying, because nobody has, because you cannot, because the cloud has never opened for anyone and never will.
— It’s like living inside a lampshade, said Cormac.
— It is exactly like living inside a lampshade, said Sarala, — and in about an hour, if you stay at that window, you will see the only weather there is, and then you will stop being rude about it.
He stayed out of politeness and then stayed another forty minutes out of something else, because what came up over the edge of the world was the bow.
Down on a surface nobody can see, the atmosphere runs into a highland the size of Africa and goes up over it, and the wave this makes stands in the air above the highland: a bright thermal bow ten thousand kilometres from end to end. It does not move. The entire atmosphere pours through it westward at a hundred metres a second and the shape stays exactly where it is, because it is not made of air. It is made of the air’s objection to a mountain.
— That’s standing still.
— That’s standing still.
— In a hurricane.
— For about four billion years, said Sarala. The wind is the thing that moves. The wave is the thing that stays. Most people get it backwards the first time, and some never stop, and I have been told I am one of them.
⁂
Cormac Dillane’s doctorate was in extremophile microbiology and his job on Perpetua was looking after a seismic payload, and if you want to know what that costs a person you had only to watch him on the evening of his twelfth day, three drinks into the monthly ration, holding forth to two women who had heard it before from other people and had never heard it from somebody who had actually wanted it to be true.
— It should be alive, he said. That’s all. That’s the whole of my position and I will defend it in any corridor on Earth. Everything out there is right. Pressure, right. Temperature, right. Energy, abundant — there is more light here than at Earth’s orbit. Chemistry, a buffet. And we have found phosphine, which has no business existing in an oxidised atmosphere, and then we have not found it, and then we have found it again, and the people on both sides are serious people, and the honest state of the literature is a shrug with references.
— And the acid, said Pilar.
— The acid is the least of it. We have organisms on Earth that metabolise at pH zero. We have things living in mine drainage that would eat a battery. Acid is an engineering problem and biology has four billion years of engineering. And before anybody says it — he pointed his cup at Sarala, — yes, the seeding. Of course the seeding. Earth has been hit hard enough to throw rock off the planet a hundred times, and some of that rock goes inward, and Venus is a target the size of Venus. The transfer is slow and inefficient and absolutely nonzero. Over four and a half billion years, with Earth running a biosphere the whole time, the idea that nothing of ours has ever arrived here is not conservative. It is eccentric.
— So why isn’t it alive, said Cormac, to himself, and answered himself, which is what he had come to Venus to do.
— Water, said Sarala.
— Water, said Cormac, and put the cup down. Everybody always wants it to be the heat or the acid, because those are frightening, and it is neither. It is that those droplets are not water with acid in them. They are acid with a rumour of water in them. The thing that matters is how much of the water is actually available — not how much is present, how much a cell could get hold of. And in that cloud it is a few thousandths. The driest thing any organism on Earth has ever been shown to grow in is about six tenths. Not six percent. Six tenths of the scale, and we are at a few thousandths of it, and that is not a hard environment, it is two orders of magnitude outside the hardest environment life has ever managed anywhere, in a direction where there is nothing to adapt to. You cannot evolve a way around not having water. There is no trick. Water is where the chemistry happens.
— And if something did, said Pilar.
— Then it is not doing our chemistry, said Cormac, — and it is the most important discovery in the history of the subject, and I would walk into that cloud without a suit to see it. Which is the other half of my position and is why I am not allowed to write reviews.
Sarala, who had been quiet, said:
— And then there is us.
Cormac looked at her for a moment.
— And then there is us, he agreed.
— Say that part.
— Nobody enjoys this part.
— Say it anyway, said Sarala. You’ve been here twelve days. It took me four years to work it out and somebody should have told me on the second.
— We are warm and wet and shedding, said Cormac. This station has been in these clouds for nineteen years. Every seal leaks a little. Every excursion carries something out. And whatever lives in our water loop is the most travelled microbial community in the inner solar system and it has been quietly introduced to the top of the Venusian cloud deck every single day for nineteen years. The acid and the dryness will have killed essentially all of it, essentially at once. But essentially is not a word with a number in it, and the consequence is that if anybody ever does find a cell up here, nobody alive will ever be able to prove where it came from. That question closed the day the first station arrived. We did not answer it. We ended it.
— And that bothers you.
— It is the reason I’m on a seismic payload, said Cormac, with the brightness people use for the thing that actually hurts. Pilar, pass the bottle.
⁂
The breathable air holds the station up, and in a decade of trying Sarala had never managed to make anybody on Earth feel it properly.
Venus’s air is carbon dioxide and heavy. Nitrogen and oxygen at the same pressure and temperature is a little over half as dense. So ordinary air — the air in your lungs, in a room, the air you are not thinking about — is a lifting gas here, as buoyant against Venus as helium is against Earth.
Perpetua’s envelope is fourteen thousand cubic metres of breathable atmosphere inside a fluorinated film, and the gondola hangs under it and is plumbed into it, and so the station floats on its own fitness to be lived in.
Pilar owned the envelope, ran a drill on it every six days, and her briefing to Cormac was the shortest and least comforting document aboard.
— Everything that goes wrong here is the same thing going wrong, she said. There is one gas. You breathe it and it holds us at fifty-four kilometres where it is twenty-seven degrees. Lose it and we do not get a leak now and a separate problem later. We go down, down is hotter, hot makes the film soft, soft loses more gas. The failure feeds itself. At forty-eight it is seventy-five degrees outside. At forty, two hundred. At the ground, four hundred and sixty-five, and nothing anybody has ever built has lasted two hours down there.
— How long would we have?
— From a square metre of seam, about seven hours before I stop enjoying myself, said Pilar. Which is plenty. Which is why we will all be very calm when it happens, and it will happen, because I have patched this envelope fourteen times and I will patch it again, and that is a Tuesday and not an emergency.
— Fourteen times.
— The acid gets in at the seams, said Pilar, with the affection of a woman describing a difficult but beloved relative. It is extremely patient. It has nothing else to do.
⁂
What Sarala had been doing since her second year was listening to a planet nobody has been able to listen to.
Venus has no seismic network and will not get one, because a seismometer must sit on the ground, and the ground is at four hundred and sixty-five degrees under ninety-two atmospheres, and the survival record down there is a couple of hours and was set in the nineteen-eighties by people entitled to be smug about it.
So nobody knows whether Venus is geologically alive. Its surface is young, almost uniformly, a few hundred million years, which is a strange thing for a planet to be and has produced a literature of competing resurfacing theories that nobody can test. The only way to test them is to catch the planet moving.
And a quake makes a noise, and here the noise comes upstairs.
— Explain it to me as if I were a payload specialist with a doctorate in the wrong subject, said Cormac.
— Earth’s air is thin, said Sarala. When the ground shakes on Earth it mostly doesn’t bother telling the atmosphere — the air is too flimsy to push efficiently, about a thousandth of the energy gets up. Down there the air at the surface is sixty-five kilograms a cubic metre. A tenth the density of water. The ground isn’t pushing a gas, it’s pushing something closer to a liquid, and the coupling is better by a factor of sixty or so. A quake on Venus is a drum skin hitting a wall of soup.
— And it climbs.
— As infrasound. Below hearing. Hundredths of a hertz to a few hertz, nothing an ear could use. Two and a half minutes to climb fifty-four kilometres, spreading, losing the high frequencies on the way, and what arrives is a few millipascals doing something unusual for a couple of minutes.
— And you’ve been catching those.
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— I have been catching something since my first year, said Sarala. Two hundred and six of them. The reason I am not a famous woman is that nobody believes me, and the reason nobody believes me is that they are right not to.
⁂
Nobody believed her because the atmosphere of Venus makes the same noise as Venus.
Gravity waves — the ordinary kind, air bobbing against its own buoyancy — run through that atmosphere constantly. Convective cells turn over. The bow over the highland sheds. The envelope breathes and flexes and radiates pressure fluctuations into exactly the band she was listening in, which is why the treadmill was banned at four in the morning and why Pilar had once been forbidden to sneeze during an observation window and had never been allowed to forget it.
Every one of those makes a small slow disturbance of a few millipascals lasting a couple of minutes.
— So you can’t tell, said Cormac in the galley on his nineteenth day, in the tone of a young man who believes he is helping.
— Not with one sensor.
— Then the honest answer is that you have two hundred and six unexplained wiggles and most of a decade.
— That is the honest answer, said Sarala, pleasantly.
— And you stayed nine years for it. Three rotations. You turned down three rotations — everybody reads the file on the way out. You could have had the Mars chair. They held a fellowship open for a year.
— They did.
— So what I don’t understand, said Cormac, who was twenty-nine and had not yet learned that there are two or three sentences a person should set down slowly and back away from, — is how anybody decides that staying in one place for nine years is the fulfilment of anything. Doesn’t it just become the thing you did instead?
The galley on Perpetua is two metres by three. There is nowhere to go.
— Sarala, said Pilar, without looking up.
Sarala held her breath for roughly the duration of an infrasound event and let it out.
— I’m going to get some sleep, she said, and did not slam the hatch, because the hatch is a pressure seal and you do not slam it, so the entire feeling went into closing it with enormous care.
Pilar waited for the latch.
— Do you want to know what you did, she said, — or find out slowly over four months?
— I’d like to know.
— You asked a woman who gave nine years to one question whether the nine years were the point. They were not. They were the price. She has known it to the month since about year five, and the only mercy available to her is that nobody says it at breakfast.
Cormac sat there for a while.
— I gave up a field, he said eventually.
— I know.
— She gave up everything else to keep one. I’m aware of the asymmetry. I was aware of it while I was saying it.
— Then you know what to do about it, said Pilar, — and it is not an apology, because she will refuse one, and it will cost you four months.
⁂
The discriminator existed, was free, and was horrible.
A quake’s infrasound comes up from below and arrives travelling nearly vertically, having climbed fifty-four kilometres through a medium whose sound speed falls steadily with height. An atmospheric gravity wave at this level is doing something else: travelling nearly horizontally, with the wind, through the layer the station sits in.
One sensor at one altitude cannot tell them apart. Two sensors separated vertically can — and the separation does not have to be in space. It can be in time.
Take Perpetua down four kilometres. Sit at fifty for a month, listening. Come back to fifty-four, listen, and compare the arrival statistics against the sound-speed profile. Vertical arrivals change their timing and their shape in a way that four kilometres of Venusian atmosphere makes very specific. Horizontal ones do not care.
At fifty kilometres the outside temperature is about seventy-five degrees. At fifty kilometres the acid in the droplets is at its most concentrated. And the station was certified for a nominal float of fifty-four with a short-excursion floor of fifty-one.
— You want to take my envelope three kilometres under the certified floor and park it there for a month, said Pilar.
— Thirty-one days.
— In the acid.
— In the acid.
— Sarala, said Pilar. I am not saying no. I am saying the film goes soft at seventy-five, that every seam I have ever patched is a seam the chemistry chose, that at fifty the droplets are at their nastiest, that I will not sleep for any of it, and that you knew all of that and came to me anyway, which means you think it is worth it.
— I think it is worth it.
— Then I need a reason I can put in writing, said Pilar, — because I have been listening nine years and I cannot stand it any more is a motive, not a reason, and the difference will matter when this is reviewed, and it will be reviewed.
⁂
The reason went to Earth and came back a hundred and four minutes later, because Venus was near the far side of its orbit and the light was taking fifty-two minutes each way.
This is the thing about the Venus desk that does not exist anywhere else, and it has to be felt rather than stated.
You ask a question. Then you go away, because there is nothing else to do with the next hour and three quarters. Sarala asked Aino Virtanen, once, in the middle of a technical exchange, whether it was still raining in Helsinki, and then went and heated a bowl of soup, and ate it, and washed the bowl, and did the socks, which on Perpetua is a bucket and a wringer and twenty minutes, and cleaned the intake screen on the number two barometer because it was due, and sat down to read, and got four pages in, and had entirely stopped thinking about Helsinki.
And then the speaker said, in Aino’s voice, out of nothing:
— It stopped about an hour ago. There is that light at the end of a wet afternoon that makes the whole street look varnished. I walked the long way back.
It is a crippled sort of intimacy and it has one enormous advantage, which is that it is the easiest thing in the world to confess into. You are not speaking to a person. You are speaking into a tube with a person at the end of it who will not react for fifty-two minutes, by which time you will be asleep, or working, or will have thought better of it and gone on with your day regardless, because there is no taking it back and therefore no point in the particular agony of wondering whether to.
Over the years Sarala had said things into that tube at four in the morning that she had never said to anybody with a face. The replies always came when she had moved on, answering a version of her that had ceased to exist two hours earlier, which should have been unbearable and was instead, somehow, the most restful relationship she had.
The approval, when it arrived, was in the same voice.
— Perpetua, Virtanen. Your reason is adequate and the office approved it in four minutes, which is the fastest they have ever done anything and tells you what they think of the catalogue. Pilar: the film people have sent a note which reads, exactly, this is within the envelope of what we did not test. I believe that is a yes.
A pause, and not a light-time one.
— And Sarala. I went back through the log, because I am that sort of person. You first described a whisper to me on day forty-one of your first year. I wrote interesting in the margin, which is the most cowardly thing I have ever written professionally, and I have thought about it from time to time since. I am looking forward to the thirty-one days. Virtanen out.
Cormac, who was in the bay and had no idea what he had just heard, said:
— She sounds all right.
— She’s all right, said Sarala, and went to check the ballast.
⁂
They went down on a Tuesday, over the night side, at the rate of a slow lift, and the thirty-one days that followed were the worst and best month any of them had.
What nobody tells you about descending on Venus is that it gets brighter before it gets darker. At fifty-four you are near the top of the cloud; at fifty-one you are properly inside it, and the light that came from everywhere starts coming from everywhere more. The port went from the inside of an eyelid to the inside of a lamp. Still no shadows. Still nothing with an edge.
The hull gauge came up like a tide. Thirty-one. Forty. Fifty-two. Sixty-nine. Pilar watched it with her arms folded and said nothing for ninety minutes, which from Pilar is shouting.
Then the station settled at fifty and began, slowly, to become unpleasant.
The thermal loop was the first thing. At fifty-four the radiators are working; at fifty they are arguing. The pumps went to a note none of them had heard before, a hard continuous hum through the deck plates that you stopped noticing in about a day and then noticed again every time it changed pitch, which it did, and which woke everyone every time it did. The gondola held at twenty-six degrees, which is fine, which is a number, and which says nothing about what it is like to live inside a box whose walls are warm on the outer side. The bulkheads were at thirty-four. You leaned on one by accident and took your arm away.
Nobody could sleep uncovered, because the standing order on an acid platform is sleeve and ankle at all times, in case, so everybody slept in a thin coverall in a cabin whose air was fine and whose walls were not, and woke up with the fabric stuck to the backs of their knees.
And on the third day the taste arrived.
It is not a smell exactly, because the scrubbers deal with the smell. It is a taste, at the back of the teeth, faintly metallic and faintly sour, from ingress so small that the sensors call it zero and the tongue calls it something else — a few parts in a billion coming through the regenerator beds, the sulfur chemistry doing to the inside of a mouth what it had been doing to the outside of the envelope for nineteen years. It never got stronger. It never went away. Cormac described it as licking a coin in a thunderstorm and then would not stop saying so.
— How long have you had it, he asked, on day six.
— Three days. You?
— Three days.
— Pilar’s had it since day two, said Sarala, — and hasn’t mentioned it, and will not, so don’t.
And over all of them, all the time, the bag.
At fifty kilometres the envelope was warm and soft and six degrees over its design point, and a hundred-metre structure of heated polymer in an atmosphere that is pouring past does not hold still. It moans. Not a creak — a long, low, slow, organic sound coming down the risers into the roof of the gondola, rising and falling at the pace of the station’s motion, exactly like something enormous breathing in its sleep two metres above your head, every minute, for thirty-one days.
On the fifth evening Cormac put his cutlery down and said:
— Does anybody else keep wanting to say shh to the ceiling?
— Every night, said Pilar.
— Thank God.
— It is not an emergency, said Pilar. It is a noise a tired material makes. I want everybody to be clear that if it stops, that is the emergency.
Nobody slept well again after she said that, which she knew, and which she said anyway, because it was true.
⁂
The catalogue filled.
By day thirteen they had nineteen events and the timing statistics had begun to do something, and Sarala had stopped sleeping in any pattern a doctor would endorse, and Cormac — who had turned out, under the one terrible sentence, to be extremely good, and to have the specific humility of a man who has decided to shut up and work — was running every waveform fit twice, independently, by hand, because she had asked and because he had worked out on his own that she needed somebody who had not spent a decade wanting a particular answer.
On day fifteen it went wrong.
A convective episode came through — ordinary, expected, the atmosphere doing its job — and for fifty-one hours the record was mud. Not noisy: smeared. Everything in the band at once, wandering, with structures in it that looked exactly like the thing she was hunting if you wanted them to, which she did, which is the whole problem with looking for something.
She sat with it for a night and a day.
And somewhere in the small hours of the second night, with the pumps grinding and the bag moaning over her head and the taste of metal on her teeth and fifty-one hours of beautiful meaningless data in front of her, Sarala Venkataraman believed, fully and without reservation, for about forty minutes, that Cormac had been right.
Not that she might be wrong. That she was wrong, and had been wrong since year one, and that the catalogue was two hundred and six fluctuations of her own air handling, and that she had spent nine years, three rotations and a particular shape of life on the noise a fan makes, and that she had built around it a method, a vocabulary and a reputation for integrity so that nobody, including herself, would ever have to say the simple thing out loud, which is that it is possible to be careful and rigorous and honest and to have wasted your thirties on a wiggle.
She did not cry, which she regards as a failure of efficiency, because it would have taken less time.
At some point she wrote in the notebook, which was not the log: If it is the air, I will publish it as the air and I will not say anything to anyone and I will take the Mars chair if it is still open, which it is not.
Then she slept four hours, and woke, and the convection had passed, and on day eighteen there were two clean events, and she worked.
She has never told Cormac about the forty minutes. She told Aino, at four in the morning, into fifty-two minutes of nothing, and got back, two hours later, a reply that began: I have had that night about the desk. Mine lasted three days. Here is what I did, and it is not advice, because it did not work.
⁂
On day nineteen the seam went.
Upper equator of the envelope, about two thirds of a metre, and the first anybody knew was the altitude trace bending, gently, downward.
— Mine, said Pilar, already moving. Suit up, both of you, you are holding lines. Sarala, you are not coming inside.
— Pilar —
— The second most useful person for this job is you and the most useful is me, and if we are both inside and it goes badly there is nobody out here with a hand on the valve. This is not about your nine years. Hold the line.
Going inside a balloon is not like anything else.
It is fourteen thousand cubic metres of breathable air at one bar, so no pressure suit — an acid suit, for what is on the outside of the film and what has come in at the tear, and a line, because the inside of a balloon is a cathedral with no floor and no ceiling, lit dirty yellow by Venusian daylight coming through two layers of polymer, with the whole vast skin of it breathing slowly in and out at the rate of the station’s motion, so that the walls come toward you and go away again, patiently, as if the thing were asleep and you were inside the sleep.
Pilar went up the internal webbing in forty-one minutes, with a patch kit and a torch she did not need, and found the tear by putting her glove near it and feeling the draught of her own station’s air going out into Venus.
She had the film unrolled and the adhesive broken open and one edge tacked, with both feet in a loop of webbing and one arm through another, when the whole envelope moved.
It was not violent. It was a long soft shove, the entire bag leaning a metre and coming back, the way a tent leans in a gust, except that there is no gust at fifty kilometres, there is only the wind you are already inside.
The patch came off the edge of the tear and folded over on itself. Pilar, hanging in the webbing with half a metre of film stuck to her own forearm and a tear open above her, said a word in Spanish that her mother would have recognised.
— Status, said Sarala, from the gondola.
— I am fine and the patch is ruined and I need the second kit. What was that?
Sarala was looking at the trace.
It had arrived at the microbarometers four seconds earlier: a clean vertical-arrival signature, the biggest in the entire catalogue, four hundred and fifty times the amplitude of the whisper that had started all this, with the dispersion exactly where the sound-speed profile said it had to be for a wave that had come up fifty kilometres from below.
It had also, because it was that big, rocked a hundred-metre bag of warm polymer with a woman hanging inside it.
— Pilar, said Sarala, in a voice that was not entirely steady. That was the planet.
— I would like the second kit.
— Pilar —
— I know what it was, said Pilar. I am inside the instrument. Send up the kit and then congratulate me in about forty minutes, and I want you to know that I am extremely happy and also that I am going to be sick, and that both of those are the adrenaline and not an opinion about your work.
⁂
And this is what had happened, four hundred kilometres below and fifty kilometres down, with nothing there to see it.
A plate of basalt, under ninety-two atmospheres, in a dim red half-light that never varies, at a temperature that would melt lead, moved against another plate of basalt by about a metre and a half.
No water. No life. No microbe, no lichen, no film of anything on the rock, because nothing survives up here in the clouds and nothing survives down there at all, so there is no witness of any kind, and there has not been for as long as the planet has looked like this. No city. No bridge. No gauge in a shed. The whole event is a shudder in a dead kettle, the hottest, stillest, most thoroughly uninhabited surface in the inner solar system letting go of some stress, as it has been doing, unobserved, at some rate nobody has ever measured, for four billion years.
And then the air above it — heavy, almost liquid, pressed down by ninety-two kilometres of its own weight — was pushed, and the push went up.
It took two and a half minutes. It lost everything fast and sharp on the way and arrived spread and slow and soft. And at fifty kilometres it moved a needle, and a bag, and a woman in a webbing loop, and that is the entire meaning that event will ever have: that there happened to be, for the first time in the history of the planet, something up here that could notice.
⁂
The month finished on a Thursday. Being sure of it took another three weeks.
Of the two hundred and six events in the nine-year catalogue and the forty-one new ones, a little under a third carried the vertical signature. They came from below. Their timing shifted between the two altitudes by exactly what the sound-speed profile demands, and their high end was gone in the way that fifty kilometres of hot carbon dioxide does to a sound and that nothing else does.
Venus moves. It has been moving the whole time, somewhere on the planet, every four or five days at a size the catalogue can see. The surface is not a dead lid, the resurfacing arguments have a measurement in them now, and the other two thirds turned out to be the atmosphere, exactly as everyone had always said, and are a magnificent dataset currently being fought over by an entirely different set of people who are also happy.
Sarala read the final fit alone in the lower bay at an hour she declines to specify, and sat with her hands flat on the table.
Then she called Earth, which took fifty-two minutes each way, so the first human being to know that Venus is seismically active had to wait an hour and three quarters to learn whether anyone had heard.
— Aino. It’s both. About a third is ours.
And then, because there was an hour and three quarters to fill and nothing to fill it with:
— I am going to say something into a recorder and you will get it in fifty-two minutes and I will not be able to take it back, which is the only reason I can say it. I have told you more at four in the morning than I have told anybody with a face in twenty years, and I have been able to do that because you cannot interrupt and I am always asleep when the answer comes. I don’t know whether that is a deprivation or a method. I would like, at some point, to find out which.
Fifty-two minutes out. Fifty-two back.
— Received, said Aino’s voice, eventually. Noticed. I have been running the same method from this end for exactly as long and I would point out that I started first. The office is on this loop, so: congratulations, it is the best piece of work this programme has produced, full confirmation attached.
A pause.
— The rest in four days, when they have gone home. Virtanen out.
⁂
Cormac asked her properly on the shuttle up to the relay, six weeks later, because by then he had earned it.
— May I have another go at the question I asked badly in week three?
— One.
— Why the nine years. Not the result — you didn’t know there would be a result. On day one of year six you didn’t know. So why.
She thought about it long enough that he assumed he had got it wrong again.
— Because the signal is four millipascals, she said, — and everything worth having is four millipascals. Every argument I ever had about this was really an argument about how long a person is allowed to look at something before it stops being research and becomes temperament. And the honest answer is that you can only hear a thing that small by not moving. Not by being clever. By staying in one place long enough that everything else about you goes quiet.
— That sounds like a virtue.
— It is a method. The virtue version is what they say afterwards if it works and the other version is what they say if it doesn’t, and both are about the same nine years, and neither describes what I actually did, which was sit in a chair in a balloon and refuse to get up.
— And the three rotations.
— Were bridges, and I burned them on purpose, one at a time, and knew exactly what I was doing each time, and it was not courage. It was arithmetic. If I had kept them I would have had somewhere to go on the bad days. There were about four hundred bad days. I would have gone.
Below the port, a long way down, the cloud went on being the colour of the inside of a lamp, and did not open, and never will.
— Can I say the thing I have been not saying for four months, said Cormac.
— Go on.
— If anything is alive down in that deck, we have already made it impossible to prove, he said. Not someday. Already. And I will spend my career on rock because of it, and I have made my peace with that in the way you make peace with a thing at two in the morning and then unmake it over breakfast. But I want you to know what I think the trade was. You gave up everywhere else to hold one question open for nine years. We — all of us, the whole programme, by arriving — closed a different one for ever, in about a week, without voting on it. And both of those are what it costs to be here, and only one of them gets a paper.
Sarala looked at the cloud for a while.
— Write that down, she said. Not for publication. Write it down so somebody has it in a notebook with a date on it. That is the entire difference between a regret and a record, and you are at the age where you still get to choose which one it turns into.
⁂
She went home the following year. Pilar had patched the envelope twice more by then and said the right thing at the handover, which was nothing at all, and shook her hand for slightly too long.
Sarala met Aino Virtanen for the first time in a corridor in Helsinki seven weeks after splashdown.
They had spoken on most working days for a decade. They had never been in a room, never shared an hour, never once had an exchange in which either could interrupt the other. The first thing that happened was that both started a sentence at the same moment and both stopped instantly, out of pure trained reflex, and waited for a light-time that was not there.
It took about four seconds.
— This is going to be a problem, said Aino.
— It is going to be an enormous problem, said Sarala, who was laughing by then.
And it was. It took them the better part of a year to learn to talk like people in the same room, and they got there, and they have been in the same city since, and Sarala still catches herself in the middle of a sentence leaving a gap where fifty-two minutes used to be.
Dynamically New
The ground started breathing seven minutes before it was supposed to, and Veronika Dvořáková felt it through her left glove.
Not a sound. There is no sound. What there is, when a patch of four-and-a-half-billion-year-old ice under a centimetre of dust first notices the Sun, is a vibration: gas forcing its way up through a porous crust at a few hundred metres a second, rasping against every pore on the way, and the whole structure conducting that into the palm of anybody stupid enough to have a hand flat on it.
It felt, she said afterwards, exactly like a cat purring in another room.
— Aminata.
— I see it.
— The terminator’s not here for seven minutes.
— The terminator is not here for seven minutes, agreed Aminata Diouf, from four hundred metres up, in the tone of a woman reading a number she had already stopped trusting. Veronika, get off that slope.
— I’ve got forty centimetres of core.
— Get off the slope.
— Forty centimetres of unheated hypervolatile stratigraphy that nobody in the history of the species has ever held, said Veronika, — out of a comet that is never coming back, and I am seventy centimetres from being finished.
There was a pause of about a second and a half, which on that crew meant a great deal.
— Four minutes, said Aminata. Then I come down and get you, and I will be extremely unpleasant about it for the rest of your life.
⁂
C/2058 F3 was a dynamically new comet, which is a technical term and also, as Matteo Serlupi observed roughly every second day, an excellent description of most of the people he had ever worked with.
It means first passage. It means this particular lump of ice and dust has been out in the Oort cloud since the solar system was assembled, at a distance where the Sun is simply the brightest star, at a temperature that has never been above about twenty kelvin, and that something — a passing star, the galactic tide, an argument among giant planets four billion years ago that is still settling — has dropped it inward, and that it is now, for the first time, falling toward the fire.
Everything about a comet that anybody has ever studied, before this, has been a comet that has already been round. Most of them have been round hundreds of times. They are burnt. The outer layers are cooked and gone, the hypervolatiles — carbon monoxide, nitrogen, methane, argon, the things that sublimate at temperatures where water is a rock — have been out of the top few metres since the Bronze Age, and what you sample is a crust, a scar, the thing the comet became after the Sun had a go at it.
Here, nothing had happened yet.
— Say it properly, Matteo had demanded, at the pre-launch briefing, because he liked hearing her say it.
— Under about a metre of this, said Veronika, — the carbon monoxide is where it was when the Sun lit. Not similar to. Not representative of. It is that. It has been at twenty kelvin for four and a half billion years, which is the same thing as not having happened yet. And in nine months it will be at one and a half astronomical units and all of it will be gone, into the coma, into the tail, into the solar wind, and it will never be anywhere again, and that is true not just of this comet but of this material, because a dynamically new comet has exactly one first passage and there is no second one, ever, and we get this one.
— And then what?
— And then it’s a used comet, said Veronika. Like all the others. Perfectly interesting. Thoroughly ruined.
Palinode carried four people out to meet it at six astronomical units, three of whom went outside and one of whom did not, by contract.
Rapee Suthep was the cryogenics officer and he lived in the sample bay, which was the coldest habitable volume on the ship and which he kept that way on purpose, and his entire professional function was to receive flasks from people who had been handling them and to make them stop handling them.
— You are warm, he said, to each of them, each time, at the hatch, with his hand out. You are a warm object. Everything about you is the problem. Give it to me and go away.
— Rapee.
— Go away.
He had three rules, posted, and the third one was the sample does not care about your morning, which Matteo had tried twice to have taken down and which outlived all of them, because it is still on the wall of a facility in Bern.
And the ship was named Palinode because the agency’s naming committee — and the agency’s naming committee — which had worked through the song forms and had arrived, by this decade, at the more technical end of prosody — had for once produced something that fitted. A palinode is a poem that retracts an earlier poem, and the ship was going to a body whose whole business, over the following nine months, was to destroy the evidence of what it had been.
— They cannot have meant it, said Matteo.
— They have never meant any of them, said Aminata.
⁂
The nucleus was three point four kilometres along its long axis, shaped like something a child had made and then sat on, and it weighed about as much as a modest hill and had the structural integrity of a meringue.
Density: a little over half that of water, which means that most of it is nothing. Seventy-odd percent void. Pores, cracks, cavities, and a crust of sintered dust over the top which is, in places, a centimetre thick and spans voids you could lose a bus in.
Veronika’s first excursion lasted five hours and she spent most of the first one lying down.
That is procedure. On a body like that you weigh about three grams. Escape velocity is somewhere under a metre a second, which is a brisk walk, so walking is not available: push off with any conviction and you do not come back. You move on lines, hand over hand, at the speed of a snail with opinions, and you do everything flat, and you learn within the first hour that the greatest hazard on the entire comet is enthusiasm.
— What does it feel like, Ingrid Haugland asked from Earth, on the open channel, because the outreach office had asked her to.
— It feels like being on a very large, very old, very fragile ceiling, said Veronika. From the wrong side.
Underfoot, when you got the dust off: ice, dark as a road. The famous thing about comets is that they are black. Albedo of a few percent, blacker than coal, because the surface dust is carbon-rich and the ice is underneath where you cannot see it, so this thing made of frost looks like a lump of soot and only gives itself away when you dig.
And the sky.
This is the part Veronika had not been prepared for and had thought she was.
At six astronomical units the comet was already active — not much, a thin leakage of carbon monoxide, because CO goes at twenty-five kelvin and will sublimate out there in the dark where water is as solid as granite. By the time they had been working on it for four months and it was inside three astronomical units, the leakage had become weather.
The coma closed the sky.
You cannot see stars through your own comet’s atmosphere once it gets going. The gas is thin by any sane standard — a laboratory on Earth would call it a hard vacuum — but it is tens of thousands of kilometres deep and full of dust, and dust scatters, and so the black absolute star-filled sky that every other airless body gives you simply goes away. It is replaced by a dim, even, faintly greenish luminosity, close overhead and in every direction, with the Sun somewhere in it as a bright smear, and nothing else at all.
— It’s a fog, said Matteo, the first time. We are standing in a hole in the ground inside a fog.
— It is the only place in the solar system where the sky closes over, said Veronika.
— That is what I said, with fewer words and a worse feeling about it.
And the dust rises. Continuously. Not fast — grains come up off the surface at centimetres a second and go past you, slowly, in ones and twos and then in handfuls, drifting upward past a person’s helmet and on out into the coma, lit by the Sun, going away for ever. You work inside a slow upward snowfall. It never lands on you. It never settles anywhere. It goes up.
Nobody had put that in a report in those words, and Veronika put it in hers, and the report was returned twice by an editor who thought it was a metaphor.
⁂
The crew’s deep-time game started on the outbound leg and ran for fourteen months and nobody can now establish who started it.
The rule was that at a meal you could say a true thing about time, and anybody who was not impressed had to produce a better one, and the loser washed up, and the washing-up on Palinode was objectively the worst job aboard.
— Stromatolites, said Matteo, on about day six. Three and a half billion years. There are living ones in Australia. You can go and look at them. They have not changed their business model in three and a half billion years and they are still on the beach.
— Weak, said Veronika.
— It is not weak —
— Sharks are older than trees.
Matteo put his fork down.
— That is not true.
— Sharks: four hundred and fifty million. Trees: three hundred and eighty-five. Sharks were swimming about for sixty-five million years before anything on land worked out wood, said Veronika. Wash up.
Aminata, who flew the ship and who had been quiet, said:
— Stegosaurus.
— What about it?
— Stegosaurus is further from Tyrannosaurus than Tyrannosaurus is from us.
There was a silence.
— Say that again, said Matteo.
— Eighty-odd million between the two of them. Sixty-six between the second one and this table, said Aminata. The two most famous dinosaurs in the world are not contemporaries. They are not even close. Put them on a sofa together and one of them is a fossil to the other one.
— Observe, said Matteo, — that our pilot has been sitting on that for six days.
— I have been sitting on that since I was twelve years old, said Aminata.
Veronika laughed so hard she had to put her head down on the table, and Matteo washed up, and that was the first evening on which anybody noticed that the two of them had stopped competing with each other and started competing as a pair against whoever else was in the room.
⁂
The science requirement was one sentence long and it was the hardest sentence anybody had ever handed her.
Return not less than two hundred grams of subsurface material at a temperature not exceeding thirty kelvin, from a depth below the thermal processing front, acquired on first passage.
Every clause in it is a problem.
Thirty kelvin, because above that the carbon monoxide starts to go and after that you are carrying an ordinary sample of ordinary cometary dust and the entire mission has been a very expensive way of confirming things known since the nineties. The flasks were actively cooled, triple-shielded, and had a thermal budget measured in minutes outside the shade.
Below the thermal processing front, because the Sun had been working on the comet for months by then, and the heat soaks downward, slowly, a few centimetres a week, and everything above that advancing front has been warmed and is therefore a used comet in miniature. The front was at about sixty centimetres and getting deeper every day, which is why the mission could not wait and could not be rescheduled and had a window measured against a line creeping down through the dark.
On first passage, because there is not a second one.
— And the alternative is a core from the plain, said Aminata, on the evening the argument started properly.
— The plain is processed to a metre twenty.
— The plain is safe. The plain is flat, it is on the night side for six hours at a stretch, it has no voids in it that the radar can see, and I can put a vehicle on it. Give me the number for the plain.
— The plain gives us about forty grams of marginal material from below the front, said Veronika, — assuming the front doesn’t move, which it will, and it is the single most valuable sample anybody has ever brought back, and it is not what we came for.
— And the other site.
— The other site is a hole in the ground with the whole of the solar system’s childhood lying exposed in the wall of it.
⁂
The hole was a collapse pit, about forty metres across, and it had not existed six weeks earlier.
This is what active comets do. Heat gets into the subsurface, volatiles sublimate out of a cavity, the roof loses the argument, and a hundred metres of crust drops into a void. It happens with no warning and it leaves a shaft with vertical walls, and the walls are a cut face through material that was buried this morning.
Within days the new face starts gassing and then it starts eroding and within a few months it is just more landscape. For a short period, it is a window.
The radar profile of the north wall showed unprocessed stratigraphy at thirty centimetres, because the collapse had taken the warmed layer away with it. Four hundred grams were available within reach of a tether. Possibly more.
The site was also, for exactly the same reason, trying to kill them.
— Give me the geometry, said Aminata.
Matteo had it ready, because Matteo always had it ready.
— The pit’s at fourteen degrees north. Rotation is twelve hours and four minutes. The north wall is in shadow for five hours and fifty minutes at a stretch and then the terminator comes over the rim and lights it.
— And when it lights.
— Then a cut face of fresh volatile ice at thirty kelvin gets full sunlight at two and a half astronomical units, said Matteo. It will go active. Not in an hour. In minutes. We have seen it on three other faces on this body and the delay between first light and first jet has been between four and nine minutes.
— And a jet does what to a person.
Veronika answered that one, because it was hers.
— A person in a suit here weighs three grams, she said. A jet from a square metre of fresh face puts out enough gas drag to exceed that by a factor of something like forty. It will not blow me up like a leaf. It will lift me off the wall at a few centimetres a second, steadily, and I will go up, and I will keep going up, and if the tether holds I will dangle in the gas stream like laundry until somebody retrieves me, and if it doesn’t I will join the coma.
— And you cannot simply move away.
— I cannot move at all quickly. That’s the problem, said Veronika. The terminator comes over that rim at about twenty centimetres a second, which is a stroll. On any other world I would walk away from it whistling. Here I go hand over hand at four centimetres a second with a core tube, and the sunrise does twenty, and it does not get tired.
— So you leave early.
— So I leave early, said Veronika, — and early is not a brave word, it is a number, and the number is forty minutes before first light on that face, and I would like everybody in this room to hear me say that out loud now so that I cannot negotiate with myself about it later.
⁂
She negotiated with herself about it later.
The first three descents were textbook. Two hundred and ten grams of unprocessed material went into the flasks in the first six-hour window, and a further ninety in the second, and the cores came up with layering in them, visible layering, bands of different volatile content that nobody had ever seen in situ, because nobody has ever had unheated material to look at.
On the fourth descent she was seventy centimetres from the bottom of a core that was going to answer a question she had been asking since she was twenty-two, and the ground began to purr.
⁂
Four minutes, Aminata had said.
What Veronika did with the four minutes is the subject of an eight-page section in the incident report, and the eight pages exist because she declined, in the review, to say that she had panicked, on the grounds that she had not.
— Explain the distinction, said the board.
— Panic is doing something without a reason, said Veronika. I had a reason for everything I did. All of my reasons were bad.
She finished the core. That took ninety seconds. The purr became a buzz under her glove and then something she could feel through her chest plate when she lay against the wall, which was a sensation she had not previously had a word for and which she now describes as being inside a very large animal that has just thought of something.
She sealed the flask. That took forty seconds, and it is the one decision in the entire sequence that the board found entirely defensible, since an unsealed flask would have made the preceding ninety seconds a waste of time and the following four minutes a waste of a woman.
And then, instead of going up the line, she went sideways for four metres to recover the second core tube, which was worth two hundred grams and which was not going to be recoverable afterwards.
The face lit while she was reaching for it.
There is no flash. The terminator on a comet is soft, because the coma scatters light around, so what happened was that the wall simply stopped being dark, over about twenty seconds, like a room when somebody opens a curtain in another room.
It was, she says, extremely beautiful.
The first jet came out of a crack a metre and a half below her boots, and she did not see it start because nothing is visible in the gas phase, and what she saw was the dust: a sheet of it, lifting off the wall, going up past her in a solid column, grains the size of flour and the size of gravel, all moving in the same direction at the same unhurried speed, like a vertical river.
Then the drag took her.
— I’m off the wall.
— Line.
— Line’s good, line’s good, I’m on the line, said Veronika, going up. She was moving, by the later analysis, at about fourteen centimetres a second, which is nothing, which is the speed of a balloon leaving a child’s hand, and which is also the single most frightening thing that has ever happened to her.
This is the horror of the place and it is the same horror as everything else about it: it is slow. There is no violence. There is no jolt, no wind, no roar. There is a steady, patient, perfectly even pressure on the back of a person, lifting her off a four-and-a-half-billion-year-old wall and feeding her upward into a cloud, at the speed of a slow lift, for as long as the Sun is on that face, which is five hours and fifty minutes.
— Tether tension, said Aminata, from above. Matteo, give me tension.
— Forty newtons. Forty-four. That is more than I would like.
— Why is it going up?
Here is what it is like inside the suit while that happens.
Outside, nothing. No sound, no wind, no weight — a wall at twenty kelvin, a sky with no stars in it, a vertical river of flour going up, all of it absolutely silent and absolutely still in the sense that nothing in it is in a hurry.
Inside, a mammal.
The pumps run at the small of her back, a continuous grinding whirr that she has not consciously heard for four months and can hear now. The fan in the helmet. Her own breathing, which has gone high and short and which she can hear arriving and leaving, loudly, because there is nowhere else for the sound to go. The suit smells of warm nylon and warm rubber and of herself, which it has done since the second week and which she notices only when frightened. There is a damp patch at the base of her spine. Her mouth has gone dry in the time it takes to say so.
And her heart, which is the only thing on that comet with any weight to it.
She weighed three grams out there. The comet’s pull on her was a thousandth of a thousandth of what she grew up under. But a heart shoves about seventy grams of blood with every stroke, and the recoil of it goes into the body, and lying flat against the wall with nothing holding her but gas and friction she could feel her own pulse rocking her, perceptibly, against a four-and-a-half-billion-year-old surface: up, and back, and up, and back, a hundred and forty times a minute, the largest acceleration in her universe, generated inside her own chest.
— Because the gas is accelerating and because she has an area, said Matteo. She is a sail. Veronika, make yourself small.
— I am extremely small.
— Make yourself smaller.
She got herself into a ball with the flask against her stomach, which reduced her area by about a third, and the tension came down, and the anchor — a screw anchor in a crust of sintered dust over a void, placed by a woman who had placed it properly, in a material with roughly the strength of a stale biscuit — held.
It held for four minutes, which was long enough for Aminata to bring the vehicle over the rim and for Matteo to get a second line onto her.
And then it did not hold.
Veronika saw it come out, because she was looking down past her own boots at the only object in the universe that was keeping her attached to anything. It did not snap. The crust around it simply let go, in a slow puff, and a circle of material about the size of a dinner plate came away and went up with everything else, and her line went slack and began to curl.
The disc of crust that had been holding her came up past her face at about the distance of an outstretched arm.
That is the first second. It is a plate of grey-black sintered dust with a screw anchor still in the middle of it, turning slowly, on its way to the Sun, and she had time to see the thread of the anchor and the circular shear mark on the underside where it had parted from the comet.
The second second is her hands. Both of them went out. There is nothing to put them on. That is a thing a body does not accept: the arms go, instantly, before any decision, and find nothing, and go again, and find nothing, and the fingers close on nothing twice.
The third second is the look down, which is the look up, because she is going up, and down is where the wall is, and the wall is now below her boots and receding at fourteen centimetres a second, and the whole of the north face is fountaining dust in a sheet that she is inside, and past the lip of the pit there is no horizon, no stars, no black — only the coma, which from in there is a pale shining nothing, forty thousand kilometres deep, uniformly lit, with no feature anywhere in it to put an eye on, and no bottom, and no top, and no end.
She has described it exactly as falling. Not floating. Falling, the way you fall in the half-second after a chair goes, except that it did not finish, and was not going to finish, and the thing she was falling into had no floor in it at any distance whatever.
The fourth second is her own voice saying a word she has declined to identify.
Then Matteo’s line caught her at the shoulder.
— Got you.
— You have not got me.
— I have got you.
— You have got my strap.
— Then shut up and let me have your strap, said Matteo, hauling, one-handed, braced against a vehicle, with the whole of the north wall now fountaining underneath them in a silent vertical blizzard that was lit from the side and was, by every account from everyone who saw it, including the one woman who was in it, the most beautiful thing any of them have ever seen.
⁂
Three hundred and ten grams came home at twenty-six kelvin.
The flasks went into a facility in Bern which had been built for this and which will not open the main allocation for another forty years, on the grounds that the instruments of 2100 will be better than the instruments of 2060 and that there is no more of it coming. Twelve grams were released for immediate analysis. The remainder sits at fifteen kelvin, in the dark, waiting for people who are not yet born, which Veronika describes as the single most optimistic thing her species has ever done with a cupboard.
The preliminary results are not the point of this story and are in any case four papers long. The short version is that the unprocessed material contained the expected hypervolatiles in unexpected ratios, that the layering is real and is being argued about, and that one class of organic molecule which everybody had assumed formed in the inner solar system turns out to have been there at the start, sitting at twenty kelvin, before there was an Earth to form anything on.
Veronika gave one interview about it and was asked, as everybody is asked, whether comets brought life to Earth, and gave the answer she had rehearsed, which is that they did not bring life, they brought shopping.
— Water and organics and nitrogen compounds, she said. Ingredients. The cooking was done here. But I would like people to understand that the ingredients are not similar to the ones in us, and they are not ancestral to them in some vague poetic way. It is the same stuff. The nitrogen in the protein in the hand you are holding this with came from somewhere, and a measurable fraction of it came off objects like that one, and the sample in Bern is a piece of the same delivery that did not get used.
⁂
There is a last thing and it is small.
C/2058 F3 went round the Sun at zero point nine astronomical units and came apart doing it, which about a tenth of dynamically new comets do. It did not explode. It did what they do: it went quiet for twelve days, and brightened, and split into four fragments, and then into a great many, and by the following spring it was a diffuse smear that the surveys tracked for another year out of politeness.
The north wall of the pit is somewhere in the inner solar system now, as a collection of particles a few microns across, spread along an orbit, and over the next few hundred thousand years some fraction of it will be swept up by the planets, and a small part of that fraction will come into the Earth’s atmosphere as meteors, which is also what happened to the material that the Earth was partly built from, which is the entire point and which almost nobody finds comforting.
Veronika watched the breakup from Earth on a screen, in Bern, in a room with a sofa in it, with Matteo Serlupi, who had taken a job in the same city, which neither of them has ever described as a coincidence and neither of them has ever described as anything else.
They had the feed up and the fragment list scrolling and a plate of bread and cheese between them and a pot of tea going cold, and they sat there for about three hours.
— Stegosaurus, said Matteo, eventually, to the screen.
— Don’t.
— Eighty million years.
— I know how many it is.
— That thing out there is four thousand six hundred million years old, said Matteo, — and it has been out in the dark at twenty kelvin the whole time, doing nothing, not changing, not being anywhere, and we went and put a hand on it and took three hundred grams and now it has stopped existing. And the stegosaurus and the tyrannosaurus and the sharks and the trees and you and me are all inside the last half a percent of it, and from where that thing was sitting we are not even separate events. There is no wall between us and anything. We are all the same afternoon.
Veronika did not answer that. She picked up the teapot, which was barely warm, and poured two cups anyway.
— Shopping, she said.
— What?
— It’s what I told the interviewer. They didn’t bring life, they brought shopping. Water, nitrogen, carbon, the organics. Ingredients.
She put a cup in front of him.
— That’s water that came in on something like that. The nitrogen in the cheese and in your hands and in the back of my neck came in on something like that. Not similar to it. The same delivery. Most of it got used and a certain amount of it did not, and three hundred grams of the part that did not is sitting in a cupboard about two kilometres from this sofa at fifteen kelvin, doing what it has done for four and a half billion years, which is nothing.
— And us.
— We are the part of the delivery that got used, said Veronika, — and then went to a great deal of trouble, over four billion years, to learn how to keep itself warm.
After a while she put her feet up on the sofa next to his, which she had not previously done, and left them there.
Out past the window, past the roofs and the sodium lights and a few kilometres of weather, the thing on the screen went on coming apart in silence.
It is silent out there because there is nothing to carry it. It was silent in that room because neither of them said anything else. And the difference between those two silences is about four and a half billion years of chemistry and one warm plate, and nothing else at all.
The fragments are still spreading. In a hundred thousand years the orbit will be a band of dust, and some of it will come down over Bern on an ordinary night in August, four or five streaks an hour, visible to anybody who is outside and looking up, and none of them will be anything.
Everything Verifies
Laleh Farahani was nine years old when she recorded herself listing the moons of Jupiter, and she had been playing the recording about once a month for twenty-six years, which is how she knew, on the four hundred and sixth day of the cruise, that the file was wrong.
Two minutes and ten seconds. A child’s voice, slightly adenoidal, going down the list in order of discovery with the terrible seriousness of someone who has rehearsed in front of a door. Io, Europa, Ganymede, Callisto, Amalthea, Himalia, Elara, Pasiphae, Sinope, Lysithea, Carme, Ananke, Leda, Thebe, Adrastea, Metis. Then a pause, a breath, and the triumphant coda, delivered to nobody: and there are sixty-three in total, but some of them are very small.
The file said sixty-one.
She played it again with the gain up, listening past her own voice for the room behind it, the radiator, the street, the particular silence of a flat at nine in the evening in a city she had not seen in four years and would not see for another two.
Sixty-one.
⁂
Out of the forward port Jupiter was the size of a pea held at arm’s length, and had been getting imperceptibly larger for a year in the way that nothing in space ever appears to do and everything in space is always doing.
It was already the most interesting thing any of them had ever looked at. At that distance the banding showed as three or four unequal stripes in cream and a brown with orange in it, and the four moons strung out along the equatorial line like beads on a wire that somebody kept re-threading: a different arrangement every evening, Io sprinting around in forty-two hours, Callisto taking sixteen and a half days to do the same lap, the whole system a clock with four hands moving at wildly different speeds and no face behind them.
Villanelle had four people aboard, nineteen months of outbound cruise behind her and six to go, and a name that Arno Weitzel had been complaining about since before launch.
— The third ship in a row named after a poetic form, he said, roughly once a fortnight, over whatever the galley had produced. Threnody. Aubade. Now this. There is a committee, the committee has a list, and at the current rate they will exhaust prosody by the end of the decade and start on heraldry, and some crew in 2051 will spend three years aboard the Bend Sinister.
— It’s a nice word, said Hae-rin Suh, who commanded, and who had learned early that the most efficient response to Arno was agreement delivered at the wrong angle.
— It is a form where two lines keep coming back in a fixed order until the end, said Laleh. For a thirty-month round trip I’d call that accurate.
— It is a form for people who cannot finish a thought, said Arno.
Daniyar Omarov, flight surgeon, the only one of them who had flown before, did not join these conversations. He listened to them the way a man watches weather.
⁂
Arno pulled the file onto his own console and listened to it twice, because he was a serious person underneath the performance.
— Sixty-one, he said. I’m sorry. It’s sixty-one.
— Jupiter has ninety-five moons, Laleh, said Hae-rin, gently.
— Jupiter had sixty-three when I was nine, and I know that because I was nine and I cared about nothing else on this earth, and the count went to sixty-four about four months later and I was insufferable about it for a week. There are sixty-three.
Arno did not argue. He ran the integrity check, which was the correct engineering response and produced the correct engineering answer.
The file verified. The block hashes verified. The partition tree verified. The scrubber log showed its usual quiet background of corrected bit-flips across the array, inside the modelled rate, nothing flagged, nothing queued. Every number on the console agreed with every other number on the console, and all of them agreed that the file was exactly as it had always been.
— Everything verifies, said Arno.
— Then something is wrong with the thing that verifies.
— That is one of the two available hypotheses, said Daniyar from the hatch, where he had been standing for an unknown length of time in the manner of a man whose job is noticing. And I had better say the other one out loud now, before somebody says it kindly.
⁂
The thing that lives out there goes through everything and does not care in the least what it is going through.
Galactic cosmic rays are the leftovers of the rest of the galaxy’s violence: mostly bare protons, some helium, and about one part in a hundred heavier nuclei stripped of every electron and moving at a serious fraction of light speed. That one part is the trouble. An iron nucleus does not stop politely at a surface. It ploughs through, and if it meets shielding it shatters into a spray of secondaries that can come out the far side carrying more damage than went in, which is why a moderate thickness of aluminium is worse than none and why the useful shielding materials are embarrassing: water, polyethylene, food, waste, and the bodies of one’s colleagues.
Inside Earth’s magnetic field you are spared almost all of it. Villanelle had left the magnetic field on day nine.
In silicon the effect is understood and designed around. A particle crosses a memory cell, dumps charge, flips a bit. The array logged tens of thousands of these a day across a petabyte and corrected every one, because the memory carries an error-correcting code and because a background process called the scrubber walks the whole array continuously, reads each word, repairs what the code says to repair, and writes it back. The scrubber was the most boring software aboard and had not raised an exception since before launch.
In a brain the effect is understood considerably less well, and is the reason there are rodents in laboratories in three countries. A single heavy nucleus crossing the cortex leaves a narrow column of ionisation, and over months a brain out here accumulates a sparse three-dimensional stippling of such columns. In animals this produces measurable losses in attention and in exactly the kind of recall where you must pull out one item against competition from similar items. In humans it produces papers in which the word suggestive does a great deal of work.
— So the same particles are going through the archive and through your head, said Daniyar, who believed in saying it plainly and then sitting down. One of those is telling us the file says sixty-one. The other is telling us it said sixty-three. Both failure modes are real, both are expected at this dose, and we have no way at all to tell them apart.
— I know what I said when I was nine.
— You are the person in this room whose instrument is in question. Nothing you report about your own memory can settle it. That isn’t an insult, it’s the shape of the problem.
— It is also, said Arno, the single most irritating sentence I have ever heard, and he is right.
⁂
What nobody had warned her about was how fast it spreads.
She lay in her bag that night with the fan going and thought, idly, about the kitchen in the flat, and found that she could not establish the colour of the tiles. Green. Possibly green. There had been a cracked one by the window with a chip out of the corner, and she could see the chip perfectly, and the tile the chip was in had no colour at all; it had the quality of a word on the tip of the tongue, present and unavailable. She lay there and tried four colours against it, and each of them fitted, which is the thing nobody tells you: a false memory does not arrive feeling false. It arrives feeling exactly like the others, with the same weight in the hand.
She got up and went to the archive and found a photograph. The tiles were a sort of oatmeal.
That should have helped and it did the opposite, because the photograph was in the same array as the recording, and she stood in the dim of the sleep station at a hundred and twenty past midnight on a Tuesday, holding a console, understanding with her stomach rather than her head that there was now nothing in her possession — not one object, not one image, not one fact about her own childhood — that she could check against anything that was not either her own brain or that machine. Both of which were being rewritten at a rate neither of them could report.
Her hands had gone cold, which in a vehicle held at twenty-two degrees took some explaining.
Over the following week she caught herself auditing, which was worse. A street name. Whether the school science fair had been in spring or autumn. Whether her father had actually said the thing she had quoted at his retirement or whether she had built it afterwards from the general shape of him. Each time, the same sensation: the floor was where it had always been and she had stopped being willing to put weight on it.
She said none of this to Daniyar for a week, because she knew what it would do to the curve, and then she said all of it in one go in the galley at six in the morning, and he listened without writing anything down, and when she finished he said:
— That’s an ordinary response to an extraordinary situation and I’m not going to call it a symptom. Also, everyone’s kitchen is beige. It is the great constant of the species.
⁂
They stated the fork properly on day four hundred and twenty-two, with Hae-rin writing it on the galley whiteboard in the handwriting of a woman who had commanded things before.
Branch one: the archive is intact and Laleh’s recall is drifting. Nothing to be done about the archive, an important medical finding, and a woman with two more years of watching herself.
Branch two: the archive is corrupting and the verification is not catching it. Then every number this mission carries is suspect — not the files that fail to open, those you notice, but the ones that open perfectly and are wrong. Calibration tables. Torque values. The pharmacopoeia. The radar library against which every return at Callisto would be matched.
— And branch two is the serious one because it’s the branch where we can’t tell we’re in it, said Arno. A file that goes bad loudly is a damaged file. A file that goes bad quietly, then gets verified and re-hashed and backed up, is not a damaged file any more. It’s just the file. It has become true.
— The code corrects upsets, said Hae-rin. That’s the whole point of the code.
— The code corrects one bit in a word and screams at two. Three bits in the same word it does not scream at, because three flips can land you on a different legal codeword whose check bits agree. It looks, finds nothing wrong, hands you a number that is not the number you stored, and certifies it. And then — he stopped, and Laleh watched the thought arrive in his face, which she described afterwards as the only genuinely frightening thing she saw on the whole flight — and then the scrubber writes it back. Every three days. Forever. In that case the scrubber is not a repair system. It is a notary.
— Three bits from one particle.
— Only if the bits of a word sit physically next to each other, which in a sane array they don’t, because you interleave them so that one ion track damages five different words by one bit each and the code eats all five for breakfast. Interleaving is the oldest trick in the discipline. It is also area and power, and on the ground, under ten metres of atmosphere and a magnetic field, you will never see the difference if you quietly take some of it out.
— And did somebody.
— I know the part number changed eighteen months before launch, said Arno, and I know the new variant was qualified in a proton beam, which produces almost no multi-bit upsets, rather than with heavy ions, which do. And I know that nothing aboard can settle it, because every tool we have for checking the archive is the archive.
⁂
What they needed was something outside the loop: an invariant that neither a cosmic ray nor a human brain could have edited.
The backup copy was no use, living in the same array under the same code with the same scrubber walking it, so that by now the two copies would agree beautifully. Earth was no use at speed; the link out there moves serious volume in weeks, and in any case what Earth would send is what Earth has, and nobody on Earth had been checking Villanelle’s copy against anything either.
It was Daniyar who remembered the glass, which was fitting, as he was the only person aboard who had read the vehicle manifest for pleasure.
— Item 9140. Fused silica, two hundred and sixteen plates, in the locker behind the water wall. There was a treaty question about whether a permanent installation’s reference data needed depositing in a durable medium, and it got resolved by somebody shipping a durable medium. Femtosecond laser pulses write birefringent nanostructures inside quartz. The data is in the orientation and strength of the birefringence, voxel by voxel, in layers through the thickness. Chemically inert, good for geological time, and completely immune to this, because nothing is stored as charge. There is no bit to flip. There is a little scratch in a rock.
— And we can read it?
— No, said Daniyar, happily. That is the beautiful part. Nothing aboard can read it. It was never meant to be read. It was meant to exist.
⁂
They read it anyway. It took five weeks and ruined a good microscope.
The principle is not exotic. Put the plate between crossed polarisers and the field goes black, because the two filters are set against each other and light that gets through the first cannot get through the second. Then the written voxels, being birefringent, split what passes through them into two components that travel at slightly different speeds, so that the light comes out the far side with its polarisation twisted by an amount that depends on what is written there — and that twisted light gets through the second filter. Black field, and in the black field the data showing as a faint ordered glow. Turn the analyser and the glow changes, and from how it changes you recover the orientation. Colourless light in at one end; at the other, a thread of brightness that was in the light the whole time and needed the right two pieces of glass to be let out.
Industrial readers do this with a modulator and a camera across thousands of voxels at once and are still slow. Villanelle had the sample-analysis microscope, built for ice and dust and decently made; the polarimeter head off the atmospheric package, which donated its filters and its calibrated rotation stage and never worked again; and Arno’s willingness to write image-processing code to a standard he described as morally unacceptable.
Nine kilobytes an hour.
It is worth being accurate about what that is like, because it is the part of the mission Laleh remembers in her body rather than in her notes. You sit at an eyepiece in a vehicle where the air is always moving and always smells faintly of hot dust and your own crew. The field is black and the voxel grid sits in it as a dim ordered scatter, dimmer than anything your eye is designed to measure, a brightness you cannot judge absolutely and can only compare against its neighbours. The stage advances in fixed increments under a thumbwheel. You read a value, you speak it, the recorder takes it. Ninety minutes of that and your eye begins to invent: the field starts producing faint structure where you expect faint structure, which is the oldest failure in observational science and the reason Daniyar imposed the ninety-minute limit and the double-keying. Double-keying caught thirty-one transcription errors over five weeks, every one of them from the humans, never twice in the same place.
They chose the Galileo-era calibration constants for the near-infrared mapper, on the grounds that they were hard numbers, unrevised since before any of them were born, on the plate, in the archive, and too dull for anyone to have touched on purpose. Six hundred and twelve kilobytes. At nine kilobytes an hour.
Arno maintained morale in his fashion.
— Day nineteen of reading a rock with a torch, he announced at supper. Forty-one kilobytes recovered. At this rate my film collection, deposited in quartz and read out by this crew, would require a campaign lasting into the next ice age, and I want it on record that I would still regard that as a sound investment.
Laleh was at the eyepiece on the fourth evening of the third week, three hours after the shift should have ended, because she had stopped being able to make herself leave.
The block was dull. All blocks were dull. It was a table of detector gain coefficients in the form of long strings of digits, and she had been reading digits for so many days that they had stopped being numbers and become shapes with sounds attached, and the archive’s version of the same table sat in the corner of the screen beside the stage controls so that the typing could be checked as it went.
Voxel row forty-one. She read the glow, called the value, and her mouth stopped halfway through the word.
The screen said something else.
She went back a column, because the obvious explanation was that she had lost her place, which happened twice an hour. She had not lost her place. She advanced and came back and advanced again, and the little dim patch sat there in the black field being, unmistakably and stupidly, a different number from the number on the screen, by one digit, in the middle, where nothing interesting ever happens.
What she felt was not vindication. It arrived first in the hands, which had begun to shake badly enough that the thumbwheel was no longer usable, and then as a kind of lurch, because she had spent three weeks in a state she had not admitted to, in which the likeliest outcome was that the glass and the archive would agree perfectly and she would spend the next twenty-two months being a woman who had been gently and expensively humoured.
She sat back from the eyepiece. The galley fan. Somebody’s music through a bulkhead. Out of the small port, Jupiter, the size now of a coin, with the shadow of one of the inner moons on it as a black dot sharp enough to look like a flaw in the glass.
— Arno, she said, into the loop, and could not immediately produce a second word.
⁂
Of the six hundred and twelve kilobytes, the glass and the archive disagreed in nine hundred and four places.
Out of roughly five million bits: about one word in six hundred, laid down across four hundred and sixty days. Small enough to have hidden inside any statistic anybody had thought to compute, and far too big to be anything but a mechanism. And not random in the way transcription error is random: the flips clustered in runs of three and four inside single words, and the words scattered evenly over the physical array, which is the signature of particles and not of a failing part.
And every one of the nine hundred and four sat inside a block whose hash was correct, inside a tree whose root was correct, because hashes had been recomputed each scrub generation rather than compared against the launch values. There was a reason and the reason was good: the archive had been recompressed in flight to make room for the radar’s raw returns, and the pre-launch hashes referred to the old blobs and had been retired as useless. A competent decision by a competent person, which had removed the only external reference in the system and left behind an arrangement capable of certifying anything.
— So it’s branch two, said Hae-rin.
— It is branch two, said Arno.
— And branch one, said Daniyar, who had the cognitive curves up on the other screen and was not going to let the room enjoy a clean result. Her slope is real and it hasn’t gone anywhere. The archive being corrupt does not uncorrupt her. Both things are happening, because the same particles are doing both, and there was never any reason to expect that only one of them would turn out to be true.
— How much of that file was me, said Laleh.
— We can’t know. Not ever. Your locker isn’t on the glass; nothing personal is. The deposition copy is reference data, the boring unfalsifiable material that treaties care about. We can prove the archive alters things. We cannot prove what your own voice said in a room twenty-six years ago, and nothing anywhere can prove it now, because the cassette went in a skip and the disc copies went with the laptop, and this was the last of it, and it has had four hundred and sixty days of iron through it.
— There are sixty-three, said Laleh.
— Probably. Very probably. I would say so on the balance of the evidence and be laughed at by anyone competent.
⁂
The remedy existed and it cost.
Arno’s third option arrived at an hour when he should have been asleep, in the form of a man in the galley doorway saying we can interleave in software. The array’s physical layout could not be changed, but what was written into it could be scattered on purpose: spread each word’s bits across widely separated addresses, and the track that crosses five adjacent cells damages five unrelated words by one bit each. The same old trick, done by the processor instead of the memory, at the price such tricks always charge. Four and a half times the space, and a read latency that would make the archive unpleasant and the radar pipeline impossible in real time.
Four and a half times the space meant that about a fifth of the archive would fit. The rest stayed in the fast array to go on being notarised into fiction.
Which meant choosing, and the choosing took six days and was the worst and in some ways the best week of the cruise, because nothing clarifies what people believe like a budget. The science corpus triaged easily — two hundred thousand papers went into the fast array without a murmur, since any result that matters appears in a dozen of them and Earth can resend anything specific in an afternoon. Calibrations, engineering data, medical reference, radar library: the spine, hardened, and that was most of the fifth gone.
Then the home lockers. Each of them had launched with a hundred and sixty gigabytes of whatever they could not be without, and the question was whether any of that belonged in a radiation-hardened partition aboard a vehicle of the state.
The programme office said no. It took four days to say it and the sentence it used was personal media are not mission-critical data products.
Hae-rin’s reply went out seven hours later, in four sentences, after she had written it three times.
— We have a documented mechanism that silently alters stored information at about one word in six hundred per sixteen months. This crew has twenty-eight months remaining. If the agency’s position is that a seismic network’s reference tables are worth protecting and the only surviving recordings of this crew’s families are not, I will implement that instruction and I will enter it in the log in exactly those words. Please confirm.
What came back, four days later, was not a triumph. It was forty gigabytes a head, signed by somebody two levels up, with a condition attached: the selections were to be itemised and submitted for review as operational morale materials, with a justification line against each entry.
— A justification line, said Arno, holding the message at arm’s length as though it smelled. Against each entry.
— Write because I want it, said Hae-rin.
— I will write because I want it a hundred and forty times and they will send it back.
He spent two evenings at it and in the end he did not write because I want it. He went through a catalogue he had maintained for twenty years, in a state no catalogue should ever be in, and he made the cut at four in the morning, and the last thing to go — he told them this once, and never again, and nobody teased him about it, which for that crew was a significant act of love — was a copy of a film he had watched with his brother thirty-one times before his brother died, and which he could obtain anywhere on Earth in four seconds, and which he was now choosing not to have for two years. He did not keep it. He kept a film he had never especially liked, because they had seen it together in a cinema, and the cinema had been demolished, and he had the ticket.
Hae-rin kept the whole of her mother’s notebooks and almost none of the music, on the grounds that music can be retransmitted and handwriting cannot. She deleted, among other things, four hours of her mother reading aloud, because there was a tape of the same book read by somebody else and she judged — in a decision she described afterwards as the most monstrous arithmetic she had ever performed, and correct — that the handwriting carried more of the woman per gigabyte.
Daniyar submitted six gigabytes on the first evening, privately, with no justification lines at all, and the programme office accepted it without comment, and that was the entirety of Daniyar’s participation in the subject.
Laleh had four hundred hours of audio. She went through it at twenty hours a day for three days, judging in the first ten seconds, which is the only way such a job can be done at all.
It is a specific kind of work. You press play, a room comes up, somebody who is now dead or now unreachable says half a sentence, and you decide. She kept almost all of the oldest material, because the oldest material had no copies anywhere. She threw out most of her twenties without much pain and was interested in how little pain. She threw out ninety minutes of a bus. She hesitated over the bus.
The thing that made it unendurable was knowing where the deleted material went. It did not go anywhere, in the sense of being erased and gone: the files would stay in the fast array, perfectly accessible, opening on demand for the next two years, slowly accumulating their one word in six hundred. What she was choosing was not between keeping and losing. It was between keeping a thing and keeping a thing that would gradually and invisibly become a slightly different thing that she would have no way of catching.
She kept the moons file, with its wrong number, and moved it to the hardened partition, where it would now stay exactly as it was for the rest of the flight, which is a strange thing to do to a lie, and which she did on purpose.
Everything verifies.
⁂
Jupiter stopped being an object and became a place over about three weeks.
The thing nobody had prepared her for, though everyone had described it, was that it does not look like the photographs, because the photographs are flat and stretched and this was a sphere with a limb — a visible curvature, a horizon of its own, cloud bands running round it and vanishing at the edges — and because it turns. It turns in just under ten hours, so fast that over the course of a single meal the whole disc rolls perceptibly and a storm you noticed on the left-hand edge arrives in the middle before the plates are cleared. Earlier, when it was small, it had been a painted marble. By three weeks out it was an engine.
The Great Red Spot came round and round again like a thing checking whether they were still there.
The moons sorted themselves out as they closed, and sorted the crew out with them, because up to then every one of the four had been secretly thinking of the Jovian system as a diagram. Io first, because Io is impossible to be fair about: a small body in a bad marriage, flexed by Jupiter and by Europa and Ganymede until the inside of it stays molten, resurfacing itself so continually that it has no impact craters at all — the only solid surface in the system with no craters, because they are paved over faster than they arrive. Through the ship’s optics it was the colour of a pizza left out, which everybody says, and which is unfortunately exact, and twice in the final month they caught a plume on the limb: a faint umbrella of sulphur dioxide standing three hundred kilometres over the edge of the disc, silent, silhouetted, falling back in a curve so slow it looked like an error in the image.
Europa was a cue ball with a scribble on it, young and smooth and cracked across by lines, and by far the most interesting place anybody could reach and by far the most lethal, and nobody aboard was going anywhere near it.
Ganymede, the largest moon in the solar system, bigger than Mercury, with its own magnetic field, came up as a visibly two-toned world, old dark ground and younger grooved bright terrain.
And Callisto, which is the one nobody writes poems about, hung further out than all of them, dark and quiet, so cratered that it has run out of room.
— The ugly sister, said Arno. The one that got none of the heat and none of the attention and none of the ocean traffic.
— It has an ocean, said Laleh.
— It has an ocean under a hundred and some kilometres of ice, said Arno, which is the planetary equivalent of having a wine cellar you can’t open.
— It also has us, said Daniyar. Which is because of the radiation, so perhaps we could be slightly nicer about it.
⁂
That is the whole of why they were at Callisto and not somewhere more exciting, and it is worth being plain about the numbers, because the numbers are extraordinary.
Jupiter has a magnetic field twenty thousand times stronger than Earth’s, and it is spinning that field round in ten hours, and the result is a radiation environment with nothing to compare to it in the solar system. Trapped particles accelerated in that field make the space around the inner moons lethal in the way a reactor core is lethal. At Europa an unshielded human being would take something near five hundred rem a day, which is a dose that kills you within a week and spends the week on it. At Ganymede it is around eight rem a day: survivable for a short visit with real shielding, unmanageable for a stay.
At Callisto it is about one hundredth of a rem a day.
Callisto orbits far enough out that it sits almost entirely beyond the worst of the belts, and that single fact is why there was a crew in the outer solar system at all. Everything else about the moon is a consequence: a base there needs no exotic protection, you can walk outside on an ordinary schedule, and the ice and dust underfoot are hydrogen-rich and make excellent shielding if you pile them on the roof, which is exactly what the cargo lander’s ploughing attachment had been sent two years early to do.
The irony was not lost on anybody and Arno made sure of it.
— I would like to point out, he said, somewhere in the last month, that the single most dangerous part of this entire expedition was the empty corridor we have just spent two years crossing, where nothing is, and that we are now arriving at the famously murderous Jupiter system in order to be safer. The dose drops when we land. We came here for a rest.
Which was true, and which is also why the archive had been quietly destroying itself during the cruise and essentially stopped once they were down. The damage was done in the empty part. There is a word for that in Laleh’s language, and there is one in most languages.
⁂
Insertion put them into Jovian orbit on a Tuesday, and they spent five weeks working down to Callisto’s orbit in a series of burns and gravity assists off Ganymede that the trajectory people had spent four years polishing and which Hae-rin flew with a concentration that left her unable to speak for an hour afterwards.
Then the landing, which is a thing worth describing because almost nobody has ever written down what it is like to land somewhere with no air at all and almost no gravity.
There is no atmosphere, so there is no aerobraking, no parachutes, no heating, no buffeting, no sound, and nothing whatever happens for free. Every metre per second of the seventeen hundred they were carrying had to be taken off by the engines. There is no terminal velocity and no glide; the vehicle is a brick with a rocket underneath it, and the rocket must run all the way down. On the other hand Callisto’s gravity is an eighth of Earth’s, so the last part of the descent is unhurried to a degree that feels deeply improper: the lander hangs, descending at the speed of a slow lift, while the surface comes up with the stately indifference of scenery on a crane.
The site was on the sub-Jovian side, in the outer rings of Valhalla.
Valhalla is the largest thing of its kind in the solar system: a multi-ring impact structure, a bright central patch with concentric ridges and troughs rippling outward across nearly four thousand kilometres of surface, frozen in place because when the impactor came in, the crust behaved briefly like a liquid and then stopped being one. The rings are not walls. After four billion years of micrometeorite grinding and sublimation they are soft swells, a few hundred metres high, with scarps on the inward side; you would drive over most of them without noticing. The mission had picked a plain between the ninth and tenth of them, flat, dust-floored, well instrumented from orbit, and as geologically boring as the planners could find, because the seismic network wanted quiet ground and because landing somewhere interesting is how you break a lander.
Dust is the hazard, and it behaves in a way nobody’s instincts handle. On Earth a rocket exhaust raises a cloud that boils and settles. There is no air here to make a cloud. The plume strikes the surface and the dust leaves on ballistic trajectories, radially, almost flat, at hundreds of metres a second, and it does not slow down and it does not come back: it goes over the horizon and lands somewhere out of sight, or leaves the moon entirely. You are not landing in a dust storm. You are operating a sandblaster aimed sideways at everything within a kilometre — which is why they came down four hundred metres from the cargo lander, with the lidar picking its way through the last hundred metres, and why the final sixty seconds were silent in the cabin apart from Hae-rin calling numbers and the pumps.
Contact was a thud up through the frame and then nothing. No settling, no creak. The engine stopped and the silence that replaced it was the real arrival.
— Callisto, said Hae-rin, for the recorders, in a voice that had gone completely flat with the effort of keeping it so.
⁂
Laleh went out second, nineteen hours later, and the first thing was the gravity.
A tenth and a quarter of Earth’s. Not the Moon’s bouncing: slower than that. You put a boot down and the ground arrives sooner than you expect, because you are heavy enough to fall properly, but a dropped tool takes well over a second to reach your feet, and you can watch it the whole way, and nobody ever stops watching. Walking is a long loping shuffle at an unhurried pace, and by the second week everybody had developed the Callisto walk, which the training staff on Earth had failed to predict and which looks, on the recordings, like four people wading.
The second thing was the ground.
It is dark. That is the part the photographs lie about, because the photographs are brightened. Callisto’s surface is dirty ice with the ice mostly gone from the top: billions of years of sublimation have carried the water away and left the non-ice material behind as a dark lag deposit, fine as talc, metres deep in the low places, the colour of old ash. Bright ice shows on steep slopes where the dark blanket slides off, so the landscape reads as dark ground with white scars on every incline, like a coal field after a frost.
And the spires.
Nobody on the crew had believed the images. Across the plain, in their thousands, stood knobs and needles of ice up to seventy or eighty metres high, dark-capped, bright on their flanks, packed close in places, scattered in others, leaning at angles. They are what is left when sublimation eats away the ground around harder material — the remnants of old crater rims and ejecta, slowly reduced to spikes and then to nothing, with the debris piling up around their bases. It is a landscape in the act of dismantling itself, and because there is no wind, no water and no air, it is doing it at a rate of a few millimetres per thousand years, so the crew walked through a forest of collapsing towers in which nothing would visibly change for the rest of the species’ existence.
— I want to go on record, said Arno, standing among them on the first excursion, that this is the most beautiful place I have ever been, and that it looks exactly like a cemetery for very tall thin people.
And Jupiter.
Callisto is tidally locked, so Jupiter hangs in one place in the sky and does not move. From the Valhalla site it stood about a third of the way up the southern sky, and it never rose and never set and never budged by a degree, for the entire duration of the mission, and it was four and a half degrees across, nine times the width of the Moon from Earth, big enough that you could not take it in at a glance but had to look from one part of it to another.
And it turned. That was the thing that none of them ever got used to. A fixed object, nailed to one patch of sky, rotating visibly in place: the bands sliding round, the Red Spot coming and going on a ten-hour schedule, the whole face reorganising itself while the thing itself never moved an inch. Twice in the first month they watched Io’s shadow cross it, a hard black dot drifting over the cloud tops, perfectly sharp, with Io itself a little way off, and that is a sight that has no equivalent anywhere a human being has ever stood.
It runs through phases, because the Sun is where it is: the phase cycles over the sixteen and a half day Callisto day, so Jupiter goes from a vast thin crescent to full and back, and when it is full it throws down something like a dozen times the light of a full Moon on Earth, which is not much and which changes everything, because it means the shadows are not black. On the Moon the shadows are absolute; there is no air to scatter light into them and nothing to fill them, and a shadow is a hole. Here, on the sub-Jovian side, the shadows have a faint brownish fill, and you can see into them, and the whole landscape sits in a soft second illumination coming from a planet, and when Laleh first noticed it she stood still for long enough that Hae-rin asked whether her suit was all right.
The Sun is a point. Bright enough to hurt, five times further than from Earth, delivering about a twenty-seventh of the light, which sounds like darkness and is not: it is a very clear day under a heavy overcast, perfectly comfortable to work in, and your brain adjusts in two minutes and never thinks about it again.
⁂
The outpost was a shed. Arno was right. It was a cylinder laid on its side with legs, a hatch, a workshop, four sleeping cubbies, and a roof under two metres of regolith which the cargo lander’s little tractor had been patiently ploughing on for two years.
The details that nobody back home ever found interesting were the ones that occupied the crew entirely.
Heat is the enemy, and not in the direction people assume. The outpost sits on ice. Anything warm sitting on ice at a hundred and thirty kelvin in a vacuum sublimates the ice underneath it, so a heated structure slowly excavates its own hollow and settles into it, out of true, at a rate that depends on the local ice fraction, which nobody can predict from orbit. The design answer is insulated footings and a jacking system, and the operational answer is that every month somebody goes out and levels the shed, which gave Arno the sentence he used for the rest of the mission whenever anything went wrong anywhere: we are sinking into our own warmth, it is in the manual.
Dust gets everywhere, in the way that only an electrostatically charged, atmosphere-free, never-weathered dust can. It is not rounded by wind or water; every grain has been fractured and never polished, so it is abrasive and it is also clingy, and it rode in on the suits and lived in the shed with them.
Which brings up the only other biology in the Jupiter system. The water loop grew its own biofilm within three months, as water loops always do, from the crew’s own skin and mouths and gut, and Daniyar spent a disproportionate share of his professional life managing a microbial community that had travelled eight hundred million kilometres and was thriving.
— They have no opinion about us as people, he said, scraping a sample. To them we are not four individuals of a species. We are a wet warm place that keeps arriving. Honestly it is the most sensible relationship anybody aboard has managed.
The seismometers went down across four excursions, in a network spread over sixty kilometres, each one dug into the regolith and coupled to solid material underneath, which is the whole problem, because the depth of the dust blanket varies from centimetres to several metres with no warning and no signature from orbit. Station three took six minutes: scrape, set, level, done, and Hae-rin said on the loop that if they all went like that she was going to start suspecting a trap.
Station four nearly killed Laleh, and it did it with dust and arithmetic, and the part she remembers is not the falling.
The site was in the lee of a spire field where the blanket had been collecting since before there was anything on Earth with an opinion. At two metres there was no bottom. At two and a half there was no bottom, and Laleh was standing in a hole up to her chest with a scoop in her hand, having a reasonable conversation with her commander.
— Depth.
— Two sixty. Still blanket.
— That’s past the shoring kit.
— It’s past the shoring kit, it’s past the plan, and it is thirty metres from the only decent bedrock signature in the quadrant, said Laleh, which is the kind of sentence people say immediately before an accident and which, in the recording, is audible as being slightly pleased with itself.
The wall went without a sound, because nothing out there makes a sound.
Callisto’s dust is not sand. Every grain has been fractured by impact and never once polished by wind or water, so the grains lock together, and the whole blanket is electrostatically sticky on top of that, and it will stand at angles that no earthly material would hold — right up to the moment it stops holding, and then it does not trickle. It goes as a unit. One second she was in a neat hole with a wall beside her, and the next she was in no hole at all, buried to the armpits, with her left arm pinned somewhere below the elbow and the right one free from the shoulder up, and the surface of the plain where her waist used to be.
The first thing is that it did not feel dangerous and this is the trap.
In an eighth of a gravity nothing crushes you. There is no weight on the chest, no pressure, no struggle for breath; a cubic metre of that dust weighs about what a large dog weighs on Earth, and the sensation of being buried in it is the sensation of being held still by something soft and entirely patient. She was annoyed. That was the whole of her emotional response for the first ninety seconds: annoyance, and a calculation about how much of the shift was now wasted.
— I’m in the hole, she said. The hole is in me. Nothing hurts, nothing’s torn, I can’t feel any strain on the left arm. Mostly I’m embarrassed.
— Stay still, said Hae-rin, already moving.
— I’m extremely still. Stillness is my entire portfolio.
Then the suit began, politely, to complain, and the complaint made no sense, because it said she was getting hot.
Here is the thing nobody tells you about standing in ice at a hundred and thirty kelvin. A spacesuit does not have a problem keeping you warm. A working body in a sealed insulated bag produces a few hundred watts of waste heat and has nowhere to put it: no air to carry it off, no water to conduct it away, nothing in contact with anything. The suit gets rid of that heat by radiating it to the sky, which is at three kelvin and is the only honest cold thing in the universe, and the radiator that does the work is a panel across the back.
The panel was now in contact with powder, and powder in vacuum is one of the best insulators that exists. There is no air between the grains to conduct, no convection, and the grains touch each other at points too small to matter, so the stuff carries heat about a thousand times worse than the solid rock it came from. She was standing in a material at minus a hundred and forty degrees, inside a vacuum flask of her own making, with her own muscles as the heating element.
The coolant return climbed a degree. Then another.
— Laleh, said Daniyar, from the shed, very evenly. What are you feeling?
— I feel cold. My hands are cold.
— Good. Your hands are always cold and they are the least informative part of you. Your core is thirty-eight point one and it has gone up by two tenths since I started this sentence. Ignore everything your skin tells you from now on. Your skin is the last instrument on this moon I would trust.
And there it was, in a hole, in the dark, with Jupiter sitting in its one place in the sky doing nothing: a number she could not check, about her own body, produced by a machine, contradicting the only direct evidence she had, which was the feeling of being a woman standing in ice and being slightly chilly.
Every person who has ever died of exertional heat stroke felt fine and then felt cold.
— Understood, she said. I’m going to stop arguing with the thermometer. It can go in the log that I stopped arguing with a thermometer in year two, which is faster than I managed with anything else.
Hae-rin had the sample scoop and got about forty seconds into digging before she understood the geometry, which she announced in the flat voice of someone cancelling a plan.
— I can’t dig you out. It comes back in as fast as I take it off. And I can’t pull you out, because I weigh nine kilos here and there is nothing to brace against, so if I pull I simply go away in the other direction at some speed and we have two problems and one of them is in orbit.
— Tractor, said Arno on the loop, from four kilometres away at the shed, where he had been spending a blameless morning jacking the outpost back to level. I am getting the tractor.
— Arno, the tractor does four kilometres an hour.
— The tractor does four point two kilometres an hour downhill and I have no intention of being reasonable about it.
Twenty-six minutes, then. Daniyar, doing his own arithmetic from a console with a woman’s core temperature on it, said nothing about twenty-six minutes, which told everybody what they needed to know about twenty-six minutes.
What saved her was Hae-rin thinking sideways instead of fast.
— Stop, said Hae-rin, half to herself, standing over the hole with a scoop in her hand. We do not have to get you out. We have to get your back out.
She did not dig downward after that. She dug a trench, a shallow trough behind Laleh’s shoulders, a hand’s depth and the width of two palms, clearing the dust off the radiator panel and holding the trough open with the lid of the shoring kit, so that the panel looked up at the black sky and at nothing else. It took her four minutes. Three kelvin is a very good customer: the moment a radiator can see it, the heat leaves and keeps leaving and does not come back.
The coolant return stopped climbing within a minute. The core temperature peaked at thirty-nine point two, sat there with the obstinacy of a thing that has got comfortable, and began, grudgingly, to come down.
The rest was unhurried and dull and took the best part of an hour, which is the correct way for an emergency to end. Arno arrived on the tractor at an approach speed that Hae-rin described in the incident report as a brisk disapproval, anchored it, let it do the only thing it had ever been built to do, which was to move regolith patiently from one place to another, and by the time the sun had moved perceptibly — which on Callisto takes a while — Laleh was lying on the surface on her back, looking up at a planet nine times the width of the Moon, laughing in a way that Daniyar later told her was textbook and harmless.
Nobody got a reprimand. The site was abandoned and the station moved forty metres onto worse rock and better ground. The suit never worked properly again: the dust got into the wrist and shoulder bearings, which nothing can be done about, because the grains are fractured glass and the bearings are not, and for the remaining months she wore the spare and complained about the gloves.
Arno’s contribution to the official record was a formal request that the ploughing tractor be entered in the log by name, that the agency be informed that its most comprehensively mocked item of equipment had now saved a crew member, and that a medal be struck. The request was denied. He had it struck himself when he got home, out of brass, and posted it to the programme office, and nobody there has ever acknowledged receiving it, and he keeps the receipt.
Which is, in the end, the reason there were people there, and the mission said so in its own documents. A machine could have done eighty percent of it for a quarter of the money. The remaining twenty percent consisted of standing in front of a hole that is not the hole in the plan and deciding, in the next four minutes, what to do, with the nearest advice ninety minutes away by radio in each direction. At Jupiter distance a conversation is not available. You cannot ask. You can only be the kind of thing that answers.
And there was the other reason, which nobody put in the documents and everybody understood: that a permanent installation with people in it is a different kind of fact from a robot, in a way that has nothing to do with science and everything to do with what a species is prepared to pay for, and that Hae-rin summarised one evening with a precision that Arno said should be engraved over the hatch.
— We are here because the seismology needs judgement, she said, and because a government wanted a photograph of somebody standing here. Both of those are true, and only one of them is embarrassing, and I notice that the embarrassing one is the one that signed the cheque.
⁂
The radar worked. That was the thing that mattered, and the hardened partition had the reference library in it, which is the reason it worked and could be shown to be working.
They got the layering in the upper ice. They got a return from depth at a boundary consistent with the ocean everyone had inferred from the magnetometer data thirty years before and nobody had ever seen. The seismic network, over eight months, recorded a hundred and some small events and three worth the trip. None of this is the story, and all of it is why there was a story.
The surface went on being peculiar every single day, which was the part that surprised the crew most, because they had all privately expected the wonder to wear off on a schedule and it declined to.
Callisto’s craters have no mountains in them. Impact into ice at these temperatures produces a shape that does not behave like rock: the big old craters have relaxed and flattened, domed up from below over billions of years, until they are shallow dishes and bright rings rather than holes, and the ancient ones are just pale rings on a dark plain, like stains on a tablecloth.
The crater density has saturated. That is a technical term with a plain meaning: the surface is so old and has been hit so often that every new impact erases an old one, so the number of craters has stopped going up. The moon has stopped keeping a record of what has happened to it. It now only shows how much has. Every new strike lands on top of an old one, erases it, certifies the surface as current, and leaves the total unchanged.
Everything verifies.
Laleh thought about that more than was reasonable.
Their footprints will be there, looking exactly as they do now, long after everything that made them is gone. No wind, no water, no weather of any kind. The only thing that will touch them is the slow rain of micrometeorites, which will blur them over some tens of millions of years, and the slow sublimation, which will lower the whole plain around them. In the meantime, four people’s boots, going out and coming back, in talc.
⁂
Here is the last of it.
The sixteenth of their months, a Thursday by the vehicle clock, which meant nothing on a moon whose day is sixteen and a half days long. Laleh was out alone at station seven, which was permitted for instrument checks, levelling a seismometer that had settled two millimetres and would go on settling.
Jupiter was nearly full and stood in its one place, and the light of it lay over the plain and filled the shadows of the spires with brown, and the Red Spot was coming round the limb the way it did every ten hours, patient as a bus.
She finished the levelling and then did what everybody on that crew did when nobody was watching, which was to stand still for a while.
She had taken her recorder out, against several rules, and she switched it on, knowing exactly what it would capture: nothing. There is no air. A microphone outside hears the suit — the fan, the pump, the rustle of a body in a bottle, the sound of a human being carrying a small amount of Earth around with her in order to stay alive. She recorded fourteen minutes of her own life support in a place where sound does not exist, and at the eighth minute, for no reason she could afterwards give, and with nothing in the frame that had changed, she laughed: one short laugh, with no explanation attached to it, the sound of somebody who has stopped wrestling with a thing and found, in the instant of letting go, that the thing was never the sort that could be won.
And she had the badge inside her glove, which was flatly against the rules: a brass school science-fair badge with the pin snapped off, carried in one pocket or another since she was nine, and in her coat pocket on the evening she made the recording. A pressurised glove is not a glove. It is a small stiff vessel that resists every movement of the hand, and through it she could feel nothing of the badge’s shape, nothing of the lettering, nothing she could have drawn. What she could feel, when she closed her fist, was the one hard edge where the pin had snapped — a burr of brass, pressing back into the base of her palm, flatly, stupidly, refusing to be the same as the material around it. It had come eight hundred million kilometres to go on being that edge.
It occurred to her, standing there, that she had been going about it backwards for sixteen months.
What she had wanted all that time was a verdict: either the archive was wrong or she was, and she would then know which of her two memories to keep and could discard the other. That was the thing she had wanted and it was never on offer, and the reason it was never on offer had nothing to do with iron nuclei. Everyone is running an archive with no external reference. Everyone rewrites it faithfully on every read and certifies each generation against the last, and the only remedy there has ever been is to go and find something that was not put there for the purpose — a rock, a plate of glass, a badge, another person who was in the room — and compare, slowly, badly, nine kilobytes an hour, and then accept that most of what you want to check cannot be checked and will have to be carried anyway.
The machine had not done anything new to her. It had merely been honest enough to be measurable.
She was not reconciled. She thought she would be eventually, in the way Daniyar had been reconciled at forty-four in a corridor over a word he could not find, and that she would know it had happened because she would stop finding it unbearable and begin finding it merely true.
In the meantime she had the file, which said sixty-one, and which she had hardened and would bring home intact, wrong, and hers.
And she had the other thing, which no instrument aboard could confirm, and which she said out loud inside her helmet, on the sixteenth month, under a planet that never moves and never stops turning, to a recorder that could hear nothing but her own breathing and the fan.
Everything verifies.
There are sixty-three.
Lift
The wings go on like a rucksack and weigh nothing worth mentioning, and the hardest part of the whole business is the straps.
— Left one’s twisted.
— It is not twisted.
— Danai. Left one is twisted.
— If you are going to stand behind me and have opinions about my shoulder, says Danai Petrakos, you can do the buckle as well.
Emil Krogh does the buckle. It takes him a while, because Titan gloves are three layers thick and the outer layer is a mitten with a split thumb, and because the two of them have been doing precisely this, in precisely this order, with precisely this exchange, every seventh day for the last three years, and neither of them is going to be the one to change it.
Outside the lock the ground is the colour of wet coffee grounds and the sky is the colour of a lampshade with a candle behind it, and nothing has an edge, and nothing has a shadow, and it is four in the afternoon in a day that is going to last another nine Earth days.
⁂
She crouches to free the trailing edge from the grit, and the suit lets her, which still catches at something in her after three years.
It bends. It has no stiffness in it anywhere, because outside is at a bar and a half, which is more than sea level at home, so the thing she is wearing is not a spacesuit and never was: it is a drysuit with a hood and a rebreather and four centimetres of aerogel batting, and it creases at the elbow like a coat. The first week she was here she sat down on the ground outside, deliberately, to find out whether she could, and then stayed sitting there long enough that Emil came out to see what had happened to her.
What finds her, while she is down there, is the cold, and it finds her at the back of the left knee, where the batting goes thin over the joint so the leg can work.
It arrives as a line. Not a chill and not a shiver — a cool band about two fingers wide drawn across the hollow behind the knee, which will be there for the next two hours and which she stopped reporting about a year ago, and which is the whole of Titan in one sensation. There is no vacuum out here to keep her warm. Vacuum is a blanket; nothing touches you and heat has to leave by radiating, and every crew that ever worked an airless body spent its time trying to get rid of heat it was making. Here a dense atmosphere at ninety-four kelvin is in contact with every square centimetre of her, five times the density of the air she grew up in, drinking out of her at a rate the suit has to fight continuously, and the number for that fight is on her left wrist.
— Heater, says Emil.
— Three twenty.
— That’s low.
— It is low because I am about to start flapping, says Danai, and you know perfectly well what happens when I start flapping.
What happens, as she comes up off the ground and feels the batting pull at her hip, is that the band behind her knee will go from cool to nothing inside four minutes, because a working body makes four hundred watts and the heater will drop to a hundred and fifty and the suit will be, for about half an hour, almost pleasant. It is the only place anybody has been where the exercise is part of the life support.
⁂
And you can hear.
Nobody is ever ready for that either. Every other world people have walked on is silent, because there is nothing to carry sound, so everybody arrives with a lifetime of documentaries in their heads in which the outside is a held breath and the only noise is a radio.
Titan is noisy. The air is dense, sound carries beautifully, and when Emil speaks four metres away Danai hears him through the atmosphere and through the hood before the radio gets around to it, so there is a sort of double-talking that everybody hates for a week and then stops noticing.
Also, in dense cold nitrogen, everybody sounds like a villain.
The speed of sound out here is about a hundred and ninety-four metres a second, well under half what it is at home, which drops every resonance in a human vocal tract through the floor, so that a perfectly ordinary woman asking a perfectly ordinary question comes out sounding like the end of an opera.
— Did you remember the spare cell, says Danai, down there somewhere around the bottom of a cello.
— Stop it.
— I am merely asking.
— You do the voice on purpose.
— I do the voice because physics does the voice, says Danai. I simply decline to fight it.
Six months of that and nobody at the station can take anybody seriously about anything, which the psychologists had flagged as a risk and which has turned out to be the single most effective thing holding nine people together on the shore of a methane sea.
⁂
— The new one asked me on Tuesday whether it’s dangerous, says Emil, from somewhere behind her left ear, because he is checking her trailing edge, because he always checks her trailing edge.
— And?
— And I told him the truth and he was disappointed. Stop flapping and you don’t fall, you sink. Wings out, two and a half metres a second, slower than coming off a kitchen chair, and you land on your feet in damp sand. Olumide came off at thirty metres in March and got up and complained about his knees for a fortnight.
— He is still complaining about his knees.
— He is a man who found a grievance, says Emil, — and that is not nothing at this latitude.
Four square metres of fabric each. That is the whole apparatus, and it holds up a woman of fifty-one plus the eighty kilograms of insulation and gas she is wearing, because the air here is four and a half times as thick as the air in a field in Denmark and the gravity is a seventh of it, and when you put those two numbers on the same side of an equation they give you something over thirty times the lift you have any right to.
She does not think about the equation. What she thinks about is her shoulders.
The wings are certified, incidentally, as unpowered personal mobility aids, which is how four sets of them came through procurement under the same line item as a walking frame, and which Emil describes as the only piece of paperwork he has ever loved.
— Ready.
— Ready.
— Count it.
— I am not counting it, says Danai. We have done this a hundred and sixty times and you still want a count.
— I like the count.
— Three, says Danai, in the voice, — two —
And they run.
⁂
Running on Titan is a drunk’s idea of running. At a seventh of a gravity your legs go where you put them and your body does not follow with any conviction, so a serious run is a series of long flat bounds, and if you lean into it the dense air pushes back hard enough to feel, like running into a swimming pool.
Four strides. Five. The ground stops being a thing she is pushing against and becomes a thing she is leaving.
The wings load up — she feels it come on across the shoulders and down into the harness at the hips, a firm even pull, not a snatch — and the horizon drops, and Danai Petrakos is nine metres up over a beach made of water-ice sand and organic grit, going out across the open flat at the speed of a bicycle, flapping twice every three seconds, in a world where nobody is supposed to be able to do this.
It never stops being the best thing that has ever happened to her. She is aware of how that sounds. She is fifty-one.
— Low.
— I know.
— You always go low on the first minute.
— Because it is better low, says Danai.
It is better low. Down near the surface the air is thickest and the lift comes easiest and the ground goes past close enough to read. Up at sixty metres everything is smooth and dull and the haze closes in and you are flying inside a brown room with no walls. Down at ten you have the dunes going past under your left wing — longitudinal dunes, a hundred metres high and running east-west for three hundred kilometres, built out of dark organic sand that fell out of the sky as haze and was swept into lines by a wind that blows, on average, at about the pace of a slow walk — and you have the ripples on the surface of them, and the little dry channel courses where methane ran last century, and the shoreline.
And then, for about forty seconds, you have the sea.
⁂
Ligeia Mare does not look like water and does not look like anything.
It is methane with ethane and dissolved nitrogen in it, it is about as clear as laboratory alcohol, and it is almost perfectly still. The wind out here cannot do anything with it: liquid methane is less dense and less viscous than water and the air above it is barely moving, so the waves on the second-largest sea on Titan run at something under a centimetre. It is a mirror the size of Lake Superior.
Which means that when you fly over the edge of it at twelve metres, what you see underneath you is the sky — the whole orange-brown vault, upside down, exactly as dim, exactly as featureless — and in the middle of it, very sharp, the small dark shape of a woman with wings.
Danai has flown over it more than a hundred times. She looks every time.
— Your reflection is better than you, says Emil, coming up on her right, three metres off and slightly low, which is where he always sits because he says the air is cleaner there and because it means she has to turn her head to talk to him.
— My reflection has better posture.
— Your reflection has both wings level.
— My reflection does not have a man behind it discussing its trailing edge.
They go out along the shore with the mirror under their left wings and the dunes under their right, two middle-aged people in insulated drysuits with four square metres of fabric each, flapping, at the speed of a bicycle, nine metres over the beach of a sea made of fuel, talking, out loud, through the air, in voices a third lower than the ones they were born with.
⁂
Here is the thing that is not in the flight log.
They were married for fourteen years. They were divorced three years and two months ago, in a process conducted largely by text with a one-hour-and-twenty-minute light-time delay in it, which Emil has described as the only civilised divorce in the history of the institution, and which Danai says is the single stupidest sentence he has ever constructed, because the delay was not civilising, the delay was anaesthetic.
There are nine people at the station. The station is a shoreline research post with two habitat modules, a workshop, a boat house that everybody still calls the boat house although the boat has been out of service for a year, and a corridor. Rotations are two years. Nobody is going anywhere.
So they worked out an arrangement, early, in the first awful month, and the arrangement is the reason this is a story about flying and not about two people being quietly horrible to each other in a corridor for twenty-four months.
The arrangement is: every seventh day, they fly. Nothing else. No meals, no shifts arranged together, no sitting next to each other at the film, and absolutely no talking about any of it on the ground. One hour out, one hour back, once a week, for as long as they are both here.
— It is a treaty, Emil told the station lead, when she asked whether she needed to be worried.
— Is it working?
— It is working very well and I would like you not to examine it.
⁂
— Left.
— What?
— Left, says Danai. Look left. Two o’clock low.
On the flat between the third dune and the shore there is a patch of ground about the size of a tennis court that is the wrong colour.
It rained here a hundred and six days ago. That is not a guess; the station has it on the met record and Danai has the photograph, because methane rain on Titan happens roughly as often as a decent snowfall in a mild country, and when it happens everybody goes out and stands in it, because the drops are nine millimetres across and fall at about a metre and a half a second and you can watch an individual raindrop come down from twenty metres up and step out of its way if you can be bothered.
The rain filled a shallow pan and the pan has been there since, going down, and today it is in its last week.
From the air it is a dull sheen with a dark rim, and the rim is where the liquid has already gone and left the sand darker and heavier than the dry sand around it. The sheen does not reflect the way the sea reflects. It has gone flat. There is a skin of something on it — fine haze particles that have been falling out of the sky onto it for a hundred days, because that is what the sky does here, continuously, forever, a slow rain of organic dust that is the reason the dunes exist at all.
— It’s going grey, says Emil.
— It has about five days.
— Five.
— Five. Say the other thing.
— I am not saying the other thing.
— Then I will, says Danai. — Five days is also the lander, and if you were going to make a point about it you have had a hundred days to make it, and you are out of time, and so is the puddle.
— I was not going to make a point about it.
— You were going to make a face about it.
— I was going to make a face about it, says Emil. I would like that distinction preserved.
— You said that two weeks ago.
— I said it had three weeks two weeks ago, says Danai, and it had three weeks, and now it has five days, and in five days there will be a slightly darker patch of sand with a rim on it and in four years nobody will be able to find it.
They go round it once, which costs them nothing and which neither of them proposed.
⁂
Forty minutes out, the arithmetic arrives, the way it does.
— Heater.
— Two ten. Yours?
— One ninety.
— You are colder than me.
— I am always colder than you, I have been colder than you since 2049, it is a documented fact and I have stopped having the argument.
Here is the arithmetic, and it is the only real constraint out here and it is not dramatic, it is a budget.
The suit carries a power cell. The cell runs the heater, and the heater runs against a dense atmosphere at ninety-four kelvin which is drinking heat off them at a rate that depends on how fast they are moving, so flying costs extra on both sides: it makes heat, which is free, and it blows cold gas over four square metres of wing and all of a person, which is not. Flapping hard is thermally about neutral. Gliding is expensive. Standing still, wet through, is the worst thing you can do.
Out and back is a hundred and twenty minutes on the cell with a reserve. The station’s rule, which Danai helped write, is turn at fifty minutes.
It is forty-one minutes.
— Say it, says Emil.
— I have not said anything.
— You are going to say it. You have had your head turned left for a kilometre and a half. You are looking at the point.
The point is Tortola Facula, four and a half kilometres ahead, where the shore turns north and a spit of brighter ground runs out into the mirror. Beyond it, across six kilometres of open sea, is the far side of the bay and a shoreline nobody at this station has ever stood on, because the boat has been out of service for a year and because nobody has ever been authorised to fly across liquid.
Nobody has ever been authorised to fly across liquid because if you come down on methane at ninety-four kelvin in a suit with a heater, you have about four minutes.
— Six kilometres, says Danai. — At four and a half metres a second, which is what I am doing now, that is twenty-two minutes across.
— And twenty-two back.
— And twenty-two back, and we have sixty-nine minutes of cell, so it fits, with eight per cent.
— It fits with eight per cent if nothing happens.
— Nothing has happened in a hundred and sixty flights.
— That is the most frightening sentence available to a person in our profession and you know it, says Emil, — and I notice you did the sum.
— I did the sum three years ago, says Danai. — I do the sum every seventh day. I have done the sum a hundred and sixty times and I have turned at fifty minutes a hundred and sixty times and I would like one person in this solar system to understand that those are not the same thing as never having thought about it.
They fly for a while.
— Can I say something unforgivable, says Emil.
— You are going to.
— I would go.
Danai turns her head properly, which costs her a little height.
— Say that again.
— I would go, says Emil Krogh, at four and a half metres a second, nine metres over the beach of Ligeia Mare, in a voice that the atmosphere of Titan has dropped a third of an octave below the one she married. If you turned north at that point I would be behind you the whole way and I would not argue once, and we would come down on the other side with eight per cent and we would be the first two people to cross a sea on another world under their own power, and it would be the best hour of my life, and I have thought about it every single week for three years.
She has begun the turn. She is not aware of having decided to.
It is small. It is one wing dropping about four degrees and a half-beat held longer on the other side, and the shore goes out of the bottom of her vision and the mirror comes into it, and for three wingbeats Danai Petrakos is flying north-northeast with nothing under her but the second-largest body of standing liquid on another world, and the far shore is directly ahead of her, and it is not far. That is what the haze does. It has no features and no depth and it will not tell you how far away anything is, so six kilometres of open methane presents itself to the eye as about four hundred metres of walking, and the whole of the west side of the bay sits there at arm’s length, mild and brown and perfectly reachable.
Nothing in her body objects. That is the part she will think about on the lander. There is no vertigo out here, no updraught, no change in the sound, no sensation of being over anything at all; the air over the sea is the same air, and the wings do not know, and her shoulders do not know, and the suit says two ten, and her own heart, in her own ears, says nothing on the subject whatsoever.
Four wingbeats. Five.
Emil has not said a word. He has come round with her — of course he has come round with her, three metres off and slightly low, where he always is — and he is not saying anything, and the radio is clear, and the only sound in the universe is fabric and harness and two people breathing, and that silence goes on for long enough that she hears herself begin to believe it.
— And? she says.
— And we are not going to, he says. Because the sum has an eight per cent reserve in it, and because an eight per cent reserve is a reserve against the things you listed, and the things you listed are not the things that kill people. And because you are the one who wrote the rule, and if you break the rule you wrote, with me, out here, where nobody can see us, then in six days when you get on the lander you will have to decide what that was, and I have watched you decide what something was, and I would not put you through it for a sea.
She holds the north heading for one more beat and then puts the wing back down.
The shore comes up into the bottom of her vision again. It takes about six seconds and it is the single most ordinary thing she has ever done.
⁂
Neither of them says anything for about two minutes, which at four and a half metres a second is five hundred metres of shoreline.
What there is, in those two minutes: the rustle of fabric, which is loud, because the air is thick; the small rhythmic creak of the harness at the hip; her own breathing in the hood; the rebreather’s little clicks; Emil’s wings, slightly out of phase with hers, audible, three metres off to the right; and under all of it the long low note that the whole of Titan makes all the time, which is wind on sand, and which nobody can record properly and everybody misses for the rest of their lives.
— It was not a mistake, says Danai.
— I know it wasn’t.
— It is simply over, and it got dull before it was over, and the dull part was worse than the over part, and I would like the record to show —
She stops.
— Go on.
— I would like it understood that I spent about a year thinking that the correct response to all of it was to be a certain kind of unhappy about it, says Danai. — The dignified kind. Quiet. Tragic. Looking out of a window. And I did it rather well and it nearly ate me, and the thing that stopped it was not wisdom and was not anybody’s advice, it was that you asked me to go flying on a Tuesday and I could not think of a reason to say no.
— I remember the Tuesday.
— You were appalling at it. You went into a dune.
— I went into a dune because you told me the lift equation wrong on purpose.
— I told you the lift equation correctly and you flapped like a man beating a carpet, says Danai.
And then she laughs, down there in the cello, loudly enough that it carries across the mirror and comes back off the far side of the bay about forty seconds later as nothing at all, because sound does not come back off anything out here, and the reason she knows that is that she has tried.
⁂
At fifty minutes exactly they turn.
It is not a moment. That is the part nobody puts in the documentaries. They turn because the clock says so, in a wide easy arc with the sea on the inside, two people in their fifties, flapping, and it takes forty seconds and Tortola Facula goes past her left wingtip and keeps going and becomes the thing behind her, and the far shore stays where it is, six kilometres away, unvisited, where it has been for four and a half billion years and where it will be next week.
Going home the wind is behind them, which on Titan means almost nothing and means something. Ground speed up by a metre a second. They come back along the inside of the dune line with the light going — not going down, because nothing goes down here for another nine days, but going thicker, the haze doing what haze does in the late part of an afternoon that is a week long, so the orange gets deeper and the little remaining structure in the sky gives up and the whole world settles into the colour of the inside of a paper bag with a bulb in it.
— Heater.
— One fifty.
— One thirty.
— You are always colder than me.
— Documented.
The rain pan goes past under them again on the way back, and it is not the same shape it was fifty minutes ago, because it is not the same size, because it is going. A hundred and six days ago something fell out of the sky and filled it and made it the brightest thing on this coastline. It has been getting duller the entire time, steadily, without any event in it anywhere, and in five days it will be a dark patch with a rim, and in four years there will be nothing to find, and all of that is simply what happens to a volume of liquid methane sitting in the open at ninety-four kelvin with a dry sky over it.
Neither of them says anything about it on the way past, which takes four seconds, and which is the second time today that both of them have declined the same remark.
⁂
They come in over the boat house and land the way everybody lands here, which is to stop flapping at about twelve metres and sink, with the wings out, at two and a half metres a second, and run four steps.
Emil runs six, because he always runs six, because he is heavier and because he refuses to come in slower.
On the ground the air is still loud. The station fans, the vent on the workshop, the sand going along the ground in its continuous unhurried hiss — Titan makes noise all day and all of its nine-day night, and the first thing everyone does at the end of a flight is stand there for a second and listen to it, and nobody has ever discussed this.
Danai gets her hood seal cracked and the outside comes in: ninety-four kelvin of nitrogen, which is not survivable for long and which is, for about one and a half seconds, the single most extraordinary smell in the solar system. It is faint and it is enormously complex and it is not like anything. The chemists have a list: ethane, acetylene, hydrogen cyanide, benzene, half a dozen nitriles. The list does not help. People who have smelled it say petrol and then immediately say no. Danai has had a hundred and sixty one-and-a-half-second exposures to it and has never written anything useful down.
— Right, says Emil, getting his straps off.
— Right.
— Thursday, then.
— Thursday.
He hangs his wings on the rack, where there are four sets and two of them have not been used in a year, and he puts his gloves in the dryer.
Then he comes back, without saying anything, and reaches round and unjams the left buckle at her shoulder — the one that was twisted, the one that is always twisted, the one that has been twisted for three years because the webbing was cut a centimetre short at a factory in Toulouse — and gets it open with the split thumb of a three-layer mitten in about four seconds, which is faster than he has ever managed it on the way out, and then he goes inside.
Danai stands in the lock for a moment with the wings half off, because that is the only part of the whole business she has never got any faster at.
Six days from now the lander goes up, and she will be on it, because her rotation is finished and because she is fifty-one and because the medical board does not re-fly people over fifty-two for a two-year shoreline posting. In seven months she will be standing in a field in Greece at nine point eight metres per second squared in air you could walk through, and she will put her arms out, once, in private, the way everybody does, and nothing whatsoever will happen.
Emil has eighteen months left and then the same.
Neither of them has mentioned it and neither of them is going to, and on Thursday they are going to fly.
Vapour Pressure
*2061. Surface pressure: 0.74 pascals.*
Jonah Ngata welds the last seam on the water wall and then sits down on the regolith for six minutes, which is against three separate rules, because the light is doing the thing.
Nobody told him about the light. They told him about the cold, which is forty kelvin and which the suit handles, and they told him about the gravity, which is a sixteenth of home and which makes a man carrying a plate of steel look like he is carrying a tray of air, and they told him about Charon, which everybody describes badly.
What nobody mentions is that the sky is blue at the edges.
Not everywhere. Overhead it is black with the Sun in it, and the Sun is a star — a single ferocious white point with no disc you could swear to, putting out about a thousandth of what it puts out over a beach in New Zealand, which is still bright enough to read a bolt torque by. But around the horizon, where you are looking along a long slant of the thin stuff, there is a band of blue. It comes off the haze, which is organic and sits in twenty-odd layers up to two hundred kilometres, and it scatters the way haze does, and the result is that a man kneeling on the night side of the coldest body anybody has ever built on sees, low all around him, the colour of a sky at home in the last ten minutes of an evening.
— Ngata, what are you doing.
— Sitting down.
— Why.
— Because it’s blue, says Jonah.
There is a pause on the loop while the shift lead looks out of a window she has not looked out of in four days.
— All right, she says. Six minutes.
⁂
*2068. Surface pressure: 0.61 pascals.*
Perla Guzmán has been told that she cannot have an oven and has decided that this is a negotiation.
What she has is forty kelvin outside, six-hundredths of a gravity, nine people, a hydroponic bay that produces chard at a rate nobody wants, and a flour allowance that arrives every twenty-six months by cargo lander with a note from an agency nutritionist which she has read once and framed.
What she makes, in the second month, out of flour and water and the air of a corridor on Pluto, is a starter.
— It won’t take, says the station engineer. It’s a closed loop. The air’s filtered to death.
— The air is full of us, says Perla.
It takes in nine days, and it is sour in a way she cannot place and did not design, because whatever wild yeast and lactobacillus got into that paste came off the hands and the breath and the skin of the particular nine people who were living in that corridor in 2068, which means it is not a Guatemalan starter and not a Terran starter. It is a Tombaugh Station starter and it is the only one.
She feeds it twice a day. Low gravity makes the dough rise wrong — it comes up too far and too slow and the crumb ends up open and wet unless she knocks it back twice, which took her four months to work out and which she wrote on a card and taped inside the cupboard door.
— You have to feed it, she tells the incoming rotation, in 2070, at the handover, with the jar in her two hands like something that might object. Every day. Not because it dies if you don’t, it doesn’t, it just sulks and goes to vinegar and takes a month to come back. Every day.
— And if we forget?
— Then it is the fault of a specific person on a specific day, says Perla, — and that person will be in the log, and in sixty years somebody will read it.
⁂
*2074. Surface pressure: 0.49 pascals.*
Marguerite Oyelaran flies the aerocapture and is the last pilot who will enjoy it.
It works like this, and the whole station exists because it works: you arrive from Earth at four kilometres a second more than you can afford, you put the vehicle through the top of Pluto’s atmosphere on a long shallow pass, and the thin stuff — one pascal of nitrogen, a pressure that would be called a hard vacuum in any laboratory on Earth — takes a kilometre a second off you over forty minutes, because there is a great deal of it spread over a very large volume and because the vehicle has a heat shield the size of a tennis court and nothing better to do.
Her pass takes nine hundred and twenty metres a second off.
The design pass, in 2057, took one thousand one hundred and sixty.
— That’s a lot of propellant, says her flight engineer, reading it off.
— That’s two hundred and twenty metres a second of propellant, says Marguerite, — which is two point six tonnes on this vehicle, which is a greenhouse or a person, and the people in 2057 did not have to choose.
She says it lightly because she has a landing to fly. She thinks about it afterwards, in the station, with a slice of Perla Guzmán’s bread in her hand, warm, and open-crumbed, and sour in a way she has never tasted anywhere else.
⁂
*2079. Surface pressure: 0.40 pascals.*
Teo Barzani is four years old and will not remember most of this, and what he does remember, for the rest of his life, is being shown how to walk.
His mother takes him out on the apron with his hand in hers, which takes forty minutes of suit checks for a seven-minute walk, and shows him the thing you do on Pluto, which is that you do not lift your feet.
You slide. At six-hundredths of a gravity a normal step throws you up and you come down forty centimetres later having achieved nothing, so everybody develops the shuffle, and children who learn to walk here learn it in the wrong order: they learn the shuffle and then they learn, later, on a ship, with a crick in the neck and a bruise on the chin, how to lift a foot.
What he remembers is the dust.
The nitrogen frost on the plain is not snow and does not behave like snow; at forty kelvin it is hard. But over it, in the hollows, is a layer of fallen haze — the tholin that has been drizzling out of the sky for four billion years, which is the colour of wet brick — and in a sixteenth of a gravity, with no wind worth mentioning, a four-year-old’s shuffling boot puts up a plume of that stuff which rises to his own helmet height and hangs, and does not come down for about two minutes, and goes orange when it crosses the Sun.
He walks the length of the apron and back making clouds and nobody hurries him.
His mother keeps a notebook for him, because she has been told to by a programme psychologist and because she would have anyway: two or three lines a week in a child’s life on Pluto, in handwriting, in pencil, which is the only writing implement that works in every room of that station. Teo made clouds on the apron. Teo asked whether Charon is asleep. Teo will not eat the chard and I am on his side.
He will be a dentist in Trieste. He will tell this badly at parties for fifty years and nobody will ever believe the part about the colour, and he will keep the notebook in a drawer with his instruments, and that is not the end of it.
⁂
*2085. Surface pressure: 0.31 pascals.*
Clement Oduya arrives to count things and is, by his own account, the most hated man ever to overwinter at Tombaugh.
He is an assets auditor. He is there for one rotation because a committee four and a half light-hours away has noticed that the station’s inventory has not been independently verified in twenty-four years, and he is good at his job, and his job consists of opening cupboards.
In the cupboard off the galley he finds a glass jar containing one point one kilograms of an uncatalogued biological culture.
— I need a line item.
— It’s the starter, says the cook.
— I appreciate that it is the starter. I need a line item, an acquisition date, a value and a custodian.
— It was made in 2068.
— By whom?
— Guzmán.
— Is Guzmán on station?
— Guzmán is dead, says the cook. In 2071. In Mexico. In a car.
Clement Oduya stands in a galley on Pluto with a clipboard, at a pressure of three tenths of a pascal, four and a half light-hours from the nearest person who could tell him what to do, and makes a decision that is still in force.
He enters it as fixed plant.
Under remarks he writes: Self-replenishing. Cannot be replaced from Earth. Loss would be permanent. And then, because he is thorough and because he is annoyed, he adds a maintenance requirement with a daily frequency, which is the only daily maintenance requirement in the entire station schedule, and which means that from 2085 onward feeding the starter is not a kindness. It is a compliance item, and somebody signs for it, every day, for forty years.
⁂
*2091. Surface pressure: 0.23 pascals.*
Ines Saldaña is the nurse and she keeps the only record anybody actually reads.
The medical log is a formal document. The other one is a notebook, and the entries are things like everyone slept badly, Charon full, which is not superstition, it is a real effect and she has the data: the station runs on a twenty-four-hour clock inside a day that is six and a third Earth days long, so once every six days the Sun comes round and nobody’s sleep survives it, and once every six days Charon is at full phase and throws enough light on the plain to read by.
Charon is the thing people get wrong in letters home.
It does not rise and it does not set and it does not move. It hangs at the same place in the sky for ever, because the two bodies are locked to each other face to face, so from the sub-Charon hemisphere it is simply nailed there, three and a half degrees across — seven times the width of the Moon from a garden on Earth — close enough that the naked eye reads the craters and the great red stain over its northern pole.
And the red is Pluto’s.
That is the part Ines writes down and sends to her sister twice. Methane escapes from the top of Pluto’s atmosphere, drifts the nineteen and a half thousand kilometres to Charon, freezes out on the one place cold enough to keep it, which is Charon’s winter pole, and there the sunlight works on it for a few million years and turns it reddish-brown. Pluto has been painting that stain for the whole of its existence out of the top of its own air.
— We are watching one thing lose its atmosphere to another thing, says Ines, to a new arrival, on the apron, at two tenths of a pascal, pointing.
— Is that sad?
— It is extremely slow, says Ines. Ask me in a million years.
The other thing in her notebook, because it arrives in her rotation and because it will arrive in everybody’s:
Once a year, a letter comes in the data packet from a dentist in Trieste. He was here as a small boy, he is now thirty-six, and he wants a photograph of the apron taken from a specific position which he describes each time in the same words — standing at the north corner of the pad with the water wall on your left — and he says each time that he is sorry to ask and that he will not ask again, and then asks again the following year.
Also, every year, without explanation, four hundred toothbrushes.
The crews deal with this differently. Some take the photograph and some forget. Ines takes it, badly, with the Sun in it, and gets back three pages about a four-year-old’s memory of orange dust that she reads twice and puts in the notebook, because it is the only document in the station’s possession that describes what this place is like to somebody who had nothing to compare it with.
⁂
*2096. Surface pressure: 0.17 pascals.*
Vuk Radich machines a replacement part for the nitrogen plant and discovers, in the process, that the floor is alive.
Tombaugh Station sits on the eastern margin of Sputnik Planitia, which is a thousand-kilometre basin filled with nitrogen ice to a depth nobody has measured, and the ice convects. Properly convects: cells twenty to thirty kilometres across, turning over on a cycle of some hundreds of thousands of years, which is why in nine hundred thousand square kilometres of that plain there is not one impact crater — the surface is wiped and renewed faster than the sky can mark it.
The station is not on the plain. The station is deliberately on the rock at the edge, because you do not build on a conveyor belt.
What Vuk finds, re-surveying his own foundation bolts against the monument that was set in 2057, is four centimetres.
Four centimetres of drift in thirty-nine years, which is a tenth of a centimetre a year, which is nothing, which is also precisely what the margin of a convecting glacier does to the shore it is leaning on.
— It’s fine, he says, in the log, and it is fine.
— Say the other part.
— In nine thousand years, says Vuk, — somebody will have to move the station four hundred metres. And in a hundred and fifty thousand years this room will be out in the middle of the plain, and in half a million it will have gone down and come up again somewhere else as a sort of stripe.
He writes the number into the foundation survey and sets a review for 2136, which is a date he will not see and which is the most optimistic thing he does in his life.
Then he goes and feeds the starter, because it is Tuesday and his name is next on the sheet.
⁂
*2101. Surface pressure: 0.12 pascals.*
Amal Haddad teaches four children in a corridor and the lesson that survives is the one she did not plan.
There are four of them, aged six to thirteen, and the eldest wants to know why they are leaving.
— Who said we were leaving?
— Everybody says we are leaving.
So Amal, who is a teacher and not an engineer, goes and gets the actual numbers off the actual engineer and comes back and does it properly on the wall, and this is the lesson.
The air out there is in equilibrium with the ground. The nitrogen ice on the plain and the nitrogen gas in the sky are in a conversation: when the ground warms a little, ice sublimates and the pressure goes up; when the ground cools, the gas freezes back onto the plain and the pressure comes down. And the relation is not gentle. It is exponential. A drop of one degree in the surface temperature does not take a few percent off the pressure; it takes a third of it.
And the ground is cooling, because Pluto is going away.
The orbit is a long ellipse. Perihelion was in 1989 and aphelion is in 2114, and over that stretch the distance goes from thirty astronomical units to forty-nine, and the sunlight falls as the square of that, so the plain is receiving less than half of what it received when Amal’s grandmother was alive. The ice is getting colder. The air is going back into the floor.
— So where does it go?
— Onto the plain, says Amal. A layer. Over a century, a few centimetres of fresh nitrogen frost over a thousand kilometres, which is the whole of our sky lying down.
— And then?
— And then it comes back, says Amal. Two hundred and forty-eight years for the orbit. Perihelion in 2237. It will all sublimate again and the pressure will come back up and there will be a sky again, and it has done this a million times and will do it a million more, and the reason people say we are leaving is not the air, it is the aerocapture.
The thirteen-year-old works it out before she finishes saying it, which is why that one is in the log.
⁂
*2106. Surface pressure: 0.082 pascals.*
Gerda Pohl makes the station’s air out of the floor — scrape the nitrogen frost, warm it, distil off the methane, electrolyse water ice from the mountains for the oxygen — and at the 2108 handover she says the only thing about it that she has ever wanted anybody to hear.
— It is the same nitrogen as the sky. Same as the floor. Same as the last lot. There is a fixed quantity of it, it goes round, we are a small warm loop inside a very large cold one, and we are not adding anything.
Then she reconfigures the plant for a deeper, softer frost, which is easier to scrape, which is the only respect in which the collapsing atmosphere has made anybody’s job better, and she writes that down with what the log preserves as satisfaction.
⁂
*2110. Surface pressure: 0.055 pascals.*
Tomasz Wierny’s wife dies in March and he stays until November, and the thing that gets him through it is a jar.
This is not sentiment. He is specific about it afterwards, to the one person who asks properly.
— I had the four-thirty slot, he says. Every day at half past four I had to go into the galley and take out a jar and throw away three quarters of what was in it and put in forty grams of flour and forty grams of water and stir it and put it back. And sign.
— And that helped.
— It did not help, says Tomasz. It was not a comfort and it did not mean anything and I was not thinking about continuity or about Dorota or about the future of the human species. It was that at half past four I was standing up.
He does it for two hundred and forty-one consecutive days and the log shows no gaps.
In September the bread goes wrong for a fortnight — flat, dense, sour in the wrong direction — and four people independently blame four different things, and what it actually was is that the galley thermostat had drifted two degrees and nobody had noticed, and Tomasz is the one who finds it, because he is the only person who touches the jar every single day and therefore the only person with an unbroken record of how it ought to feel.
⁂
*2114. Surface pressure: 0.041 pascals. Aphelion.*
Noor Alsaadi brings in the last crewed lander and does it on engines all the way, and it costs what everybody said it would cost.
The atmosphere at four hundredths of a pascal gives her a hundred and ten metres a second of braking, against the one thousand one hundred and sixty of the design pass, which means the capture has to be done propulsively, which means three extra tonnes of propellant, which means she arrives with four people and no cargo at all.
No cargo at all. That is the number that closes the station, and it is nobody’s decision.
Pluto is at forty-nine point three astronomical units today, the furthest it will be for two hundred and forty-eight years, and from here on it is coming back, and the air will come back with it, and the aerocapture will work again — around 2190, by the modelling, properly by 2220.
— A hundred and six years, says Noor, in the galley, to a room of eight people.
— Say it in rotations.
— Forty-one rotations in which this place cannot be resupplied at a sane cost.
They eat bread. It is the same bread. The starter is forty-six years old and nobody in the room was alive when it was made.
⁂
*2119. Surface pressure: 0.038 pascals.*
The mass statement is four hundred kilograms for two people and it is sitting on the galley table printed out, because Esther Mbatha has found that people argue better about paper.
Everything else is decided. The station goes into dormancy: radioisotope trickle, modules sealed, beacons live, the plant left in a condition that somebody in 2190 can bring up in a fortnight. Esther wrote that procedure herself over four months and it is a good procedure and nobody has objected to a line of it.
What is not decided, on the twelfth of August, with forty-one days to the launch window, is the list.
The list runs to nine items and they total five hundred and eighty kilograms and that is after Li Wenhao has already given up his personal allowance, which he did in the first week, without discussion, which Esther has privately decided she will not forgive him for because it removed the one argument she could have won.
Item one is a hundred and sixty kilos of the deep core. Four years of it. Sixty-eight metres of nitrogen-ice stratigraphy from the margin of the plain, drilled by a woman called Fidelma Okafor who went home in 2116 and who has written four times, each time more carefully than the last, and that core is the only physical record anybody will ever have of what the glacier was doing on the way down from a one-pascal atmosphere, and there will not be another one until somebody drills again in the twenty-third century, at a different pressure, which makes it a different experiment.
Items two to eight are instruments, two seismometers, a spectrometer head and the complete set of station logs in hard copy because Esther does not trust anything she cannot drop.
Item nine weighs one point one kilograms and is a glass jar.
— Say it again, says Li.
— It stays.
— Say the reason and not the regulation.
— The regulation is the reason, says Esther. Oduya logged it as fixed plant in 2085 with a note saying its loss would be permanent, and that note is the most accurate sentence anybody has ever written in this building, and fixed plant does not leave, and if I put a jar of bread culture on that lander ahead of eight metres of Fidelma’s core I will have to write the words that explain why, and I have tried to write them, and they come out as because we like it.
— Then write because we like it.
— I am not putting that in a dormancy document.
— Why not? says Li. Who is the document for?
Esther does not answer that for about four seconds, which Li has learned to read as the sound of a position giving way slightly and resettling.
They go round it for three weeks.
The honest difficulty, underneath the inventory, is that nobody knows what seventy years does to it, and the two available answers are both guesses.
Leave it wet, in the jar, in the galley. The galley will go to ambient within a month of the heaters dropping, which means the jar will freeze solid, and it will spend sixty-seven years at a temperature nothing on Earth has ever stored a culture at. Freezing a starter is an ordinary method of keeping one; freezing it for seven decades is not a method, it is a hope, and the ice crystals do the damage, and nobody can tell you the survival fraction because nobody has ever had the chance to find out.
Or dry it. A hundred grams on parchment, in a tube, in Li’s allowance, which means it travels, which means it also goes on a vehicle and through a capture burn and into an archive on Earth where an institution will own it, and dried starter revives well and reliably and loses diversity doing it — the drying selects, and what comes back is not the population that went in, which is the only thing about the jar that has ever mattered, because the population that went in came off nine specific people in a corridor in 2068.
Esther puts it to the microbiologist on the programme, which costs twelve hours and gets back a paragraph that says, in effect, probably, with losses, and I would do both.
So they do both.
On the ninth of September, with the modules already cold at the far end and their breath visible in the galley for the first time in sixty years, Li weighs out a hundred grams and spreads it thin on parchment under a lamp, which takes two days, and flakes it, and seals it, and labels it in two scripts.
And Esther takes the jar and puts it back in the cupboard where it has been since 2068, and the card Perla Guzmán taped inside the door is still there, gone brown, the handwriting of a woman who died in a car in Mexico when Esther’s mother was a girl, and under it Esther tapes a second card.
It reads: Feed twice daily, 40 g flour, 40 g water. Knock back twice — low gravity. She was right. If this one is gone, there is a dried hundred grams in the archive at Leiden, and it is not the same, and use it anyway.
Then she closes the cupboard, and signs the daily maintenance sheet for the last time, and the item stays open.
The two of them go out on the apron afterwards, which is not in the procedure, and stand at the north corner of the pad with the water wall on their left, and Esther takes the photograph.
It is the fiftieth one. It goes into the outbound packet to a dentist in Trieste, who is now seventy-four, and who replies twelve hours and twenty minutes later with a single line, which is in the station’s final log and which is the last thing any human being transmitted from the surface of Pluto for seventy-two years:
Thank you. That is the one.
⁂
*2124. Surface pressure: 0.037 pascals.*
Nobody is on Pluto, and nobody is going to be, and the reason is not a tragedy and not a retreat.
Nothing got invented. That is the part people find hard. The seventy-two years between the last lander and the next one were not a dark age; they were an extremely busy period in which the inner system was built out, the belt was worked, three bodies got permanent populations and the propulsion that everybody in 2119 assumed was twenty years away turned out to be forty and then sixty and then a matter for a different century. Nobody solved the problem. The problem was that a particular planet was at the far end of a two-hundred-and-forty-eight-year ellipse with its atmosphere on the floor, and the only thing that was ever going to fix that was the planet coming back, and the planet came back on schedule, because that is what planets do.
The agency that built Tombaugh does not exist. It was dissolved in 2141 and its obligations were distributed, and the institution that returns in 2191 is a different institution in a different century with a different flag, which inherited, among several thousand other dormant assets, a filing system.
Meanwhile: the station sits at forty kelvin with its heaters at trickle. Outside, over a thousand kilometres of plain, the sky is lying down — four centimetres of fresh nitrogen frost laid over sixty years, the most boring geological event in the solar system and also the entire atmosphere of a planet, folded up and put away where it will keep.
Charon hangs where it has hung for four billion years, three and a half degrees wide, with its red pole made out of Pluto’s breath.
And in the galley cupboard, frozen through, a kilogram of flour and water made out of nine people who are all dead does nothing whatsoever, extremely slowly.
⁂
*2191. Surface pressure: 0.09 pascals and rising.*
The first thing the advance party does, before the modules are warm, before the plant is up, before anybody has slept, is open the galley cupboard, because the procedure says so.
The procedure says so because a woman called Esther Mbatha put it in the dormancy document in 2119 as item 14, which caused a certain amount of comment at the time and which nobody ever took out, and which is why four people in pressure suits with their hoods back are standing in a cold kitchen on Pluto at two in the morning station time looking at a jar.
It has thawed over four days and it smells of acetone and vinegar and, under that, faintly, of something else.
Two cards are taped inside the door. The lower one is brown and brittle and was written in 2069 by a woman who died in a car in Mexico. The upper one is in ballpoint and ends: and it is not the same, and use it anyway.
They feed it. Forty grams of flour, forty grams of water, stir, sign.
Nineteen days. The first loaf is a brick and the second is worse and the fourth one works, and the four of them eat it standing up in a cold galley at six in the morning station time, and this is what it is like.
It is dense, because low gravity does that and because nobody has knocked it back properly yet. The crust gives with a sound. It is sour — properly sour, acetic at the front and lactic underneath, sharper than anything any of them has eaten, with a smell in the crumb that two of them separately describe as old petrol and one describes as a cellar and the fourth cannot describe at all.
And the sourness is a population. It is the specific assembly of yeasts and lactobacilli that came off the hands and mouths and skin of nine people standing in a corridor in 2068, maintained in an unbroken line by about four hundred individuals, none of whom met the first nine, frozen for sixty-seven years, and now in the mouths of four people who are chewing it. There is nothing else alive on this planet. There never has been. In nine hundred thousand square kilometres of nitrogen ice and water-ice mountains and organic haze the only biology is inside the station, and the oldest thing in it by a century and a half is in the bread.
Teo Barzani’s notebook is on the shelf in the galley, because the woman who has the 2191 mission’s cultural inventory is his great-granddaughter, and it was in a drawer with his instruments for fifty years, and the entry she keeps opening it to is seven words long and in pencil: Teo made clouds on the apron again.
Outside, the plain is warming by a fraction of a degree a decade and the nitrogen is coming up off the floor exponentially, a third more pressure for every degree, so that by perihelion in 2237 there will be air enough to brake a ship on, and the people standing in this galley are the ones who will do it.
The gauge on the wall reads 0.09 pascals and rising.
At half past four the next afternoon somebody opens the cupboard, takes out the jar, throws away three quarters of what is in it, weighs forty grams of flour and forty grams of water, stirs, puts it back, and signs the sheet in the nineteenth column under a compliance item that has been open since the first of October 2085.
The thermostat clicks on behind her.
Nobody says anything, because there is nothing to say about it, and the gauge goes up by a thousandth of a pascal overnight.
Notes on Scientific Plausibility
Every story in this book ends in the real world, and these notes say where. Each one names the mechanism the story turns on and states plainly how much of it is established physics, how much is standard engineering practice, and how much is extrapolation. Nothing here is required in order to read the stories. It is here so that a reader who wants to check the author’s work can do it without leaving the volume.
The Sharpness Budget
The mechanism: Self-Induced Molecular Contamination of Cryogenic Space Optics and of Decontamination Bake-Out.
The central mechanism is standard, not speculative, and it is one real reason crewed servicing of a cryogenic observatory is hard. In vacuum nothing sweeps released material away and nothing settles it out, so molecules vented by a spacecraft — outgassing materials, thruster products, leaks, and above all a spacesuit sublimator, which sheds metabolic heat by boiling roughly half a kilogram of water into space per hour of work — stay in the neighbourhood. The transport path matters and is the point of the story: the plume itself is directed away from the optics, but within centimetres of the porous plate it is dense enough to self-collide, scattering a tail of molecules to wide angles; those strike warm vehicle structure, which does not retain water but re-emits it thermally in a broad cosine distribution, including forward past the edge of a sunshade; and the molecule then travels ballistically until it meets something. Any cryogenic surface is a cold trap: water arriving at a few tens of kelvin sticks with probability near unity and does not come back off, so the layer only grows. The arithmetic is what makes this a hazard rather than a curiosity. A hundred nanometres of amorphous ice is about ten micrograms per square centimetre, of order a gram across a large aperture, while an intensive servicing campaign may vent many tens of kilograms — so a return fraction of one part in tens of thousands suffices. Such a layer is optically irrelevant in the visible and scatters strongly in the infrared, raising the wings of the point-spread function, which is exactly what a high-contrast coronagraph lives on. Astronauts have reported ice particles shed by their own vehicles since the earliest orbital flights, and contamination budgets are a formal, heavily modelled part of every observatory programme. The roll test is a genuine discriminator: a vehicle-fixed halo does not rotate in the data, a sky-fixed one does. The remedy is also real — decontamination bake-out has been performed on flight instruments — and so is its price in cryogen and lost observing time, together with the honest risk of cycling a large segmented beryllium-and-gold mirror through a thermal excursion it was never designed to repeat, where differential expansion can bind an actuator or strain a segment mount. The astronomy is extrapolated rather than invented: the planets named are real objects or real candidates around real nearby stars, and a cold mid-infrared coronagraphic observatory is the generally agreed next step for obtaining spectra of temperate rocky worlds. The reasons given for not flying a robotic servicer are the real ones: an observatory built without any servicing interface, forty cold-soaked captive fasteners with a genuine risk of cold welding, a five-second light round trip at L2 that forces move-and-wait teleoperation and multiplies task time by one to two orders of magnitude, and an autonomous alternative that costs more and arrives later than crew. Human shedding of viable microorganisms is likewise well documented, and while a mirror at thirty-nine kelvin is not an environment anything can colonise, planetary protection exists precisely because the general principle does not hold everywhere. As for the microgravity domestic physics, the constraints described — no convection, no drainage, no leverage, and Newton’s third law applied to two people and nothing to brace against — are as stated, and the resulting envelope really is narrow, which does not make it less appealing.
Sixty-Four Pascals
The mechanism: Cohesion in Rubble-Pile Asteroids, Negative Effective Gravity at the Equator, and Deflection by Thermal Means.
The object is real. (29075) 1950 DA is a near-Earth asteroid roughly 1.3 kilometres across, rotating once in about 2.12 hours, with a small but non-zero chance of striking the Earth in 2880. At that spin a cohesionless rubble pile of its estimated density should be shedding material from its equator, and the fact that it is not is the published evidence that cohesive forces — van der Waals attraction between fine grains, with electrostatic and sintering contributions — hold such bodies together; analyses of its thermal and rotational state give cohesive strengths of the order of tens of pascals, the pressure of a sheet of paper resting on a hand, which is the figure used here. The equatorial condition follows from the numbers: gravitational acceleration of a few ten-thousandths of a metre per second squared against a somewhat larger centrifugal term leaves a net outward effective gravity at the waist, so released material rises rather than falls, while fine regolith stays put because at grain scale surface forces overwhelm weight. Escape velocity is around twenty centimetres per second, so an unanchored person leaves with an ordinary push, and a prone human needs only a few hundredths of a newton of restraint, readily supplied by regolith adhering to a glove — an adhesion that has been a documented nuisance on every airless body yet visited. Horizon distance, a two-hour day with ninety-second sunrises, a visibly rotating sky, and a regolith manufactured by repeated thermal cracking rather than by weather all follow from the body’s size and spin. Sampling at small asteroids has found surfaces with almost no bearing strength that behave like a fluid under contact and throw up slow clouds taking many minutes to settle, and spontaneous particle ejection has been observed. On deflection: kinetic impactors transfer momentum efficiently, but a weakly bound pile may deform or shed mass rather than translate cleanly, and converting one object into a dispersed swarm is not obviously an improvement; the gravity tractor, which touches nothing and applies no impulse, is a seriously studied alternative for weak bodies, as is altering an object’s thermal properties, since the Yarkovsky effect — recoil from anisotropic thermal re-radiation — dominates the long-term orbital drift of small bodies and is the leading uncertainty in this particular object’s impact assessment. The requirement for independently produced assessments on decisions of this consequence, and the recognised hazard of correlated judgement in long-collaborating teams, is ordinary risk-analysis practice and not a literary invention.
Nothing Is Where You Left It
The mechanism: Lunar Polar Water, Orbit Prediction Error, Plane-Alignment Windows, Phasing, and Capture of a Flat-Spinning Vehicle.
The water situation is as described and is the usual surprise. Lunar polar volatiles are not an ice sheet but frost mixed through regolith in permanently shadowed regions at a few tenths of a percent to a few percent by mass; the LCROSS impact into Cabeus indicated a comparatively rich several percent, and much lower figures are typical. At temperatures of a few tens of kelvin that regolith is cemented into something mechanically closer to concrete than to soil, excavation and thermal extraction are energy-intensive, and the shadowed floors have no sunlight for local power, so everything runs off cable from a sunlit ridge while lubricants, seals and batteries operate far outside their design range. Hand production of ten-odd kilograms a day is a generous estimate rather than a pessimistic one. On the orbital side, prediction error along the direction of travel dominates: a small error in period accumulates with every revolution, so a second of period error becomes tens of kilometres within days while the orbit’s shape and orientation stay well known. A venting vehicle adds an acceleration that cannot be modelled, because it depends on conditions nobody can observe — the same difficulty as the non-gravitational acceleration of comets. A leak of grams per minute is negligible as mass loss and entirely sufficient as perturbation at the ten-millionth-of-a-gravity level. The lunar gravity field is genuinely lumpy, most low lunar orbits are unstable, and orbital planes precess at rates depending on altitude and inclination, so an orbit that has been altered precesses differently — the hinge of this story. Plane changes are the most expensive routine manoeuvre available, and a surface site passes under a given orbital plane only twice per rotation, about every thirteen and a half days for the Moon. The phasing argument is exact: prograde thrust raises the orbit, lengthens the period, and makes a chaser fall behind, so catching something ahead requires dropping lower and waiting, and the resource consumed is time. The flat spin is real: no body is rigid, internal flexing dissipates rotational energy while angular momentum is conserved, and a tumbling object settles into rotation about its axis of maximum moment of inertia, as happened to Explorer 1 in 1958. Axial approach to a point that rotates without translating is a recognised technique for non-cooperative capture, and angular momentum transfer at grapple, reaction wheel saturation and thruster plume impingement on the target are all standard proximity-operations concerns. Water venting into vacuum flashes partly to vapour and partly to ice crystals, is visible in sunlight, and deposits as frost on a cold surface it reaches. Surface detail is as described: at the south pole the Sun circles near the horizon, shadows are long and rotate through the month, permanently shadowed floors sit at a few tens of kelvin, dust is abrasive and does not settle through any atmosphere because there is none, launch from an airless body pitches over almost immediately because orbit is horizontal speed rather than height, and from near the pole on the nearside the Earth hangs low and nearly fixed, moving only by a few degrees of libration.
The Other Face
The mechanism: Mercury’s Polar Cold Traps, Thermal Operations in Vacuum, the Retrograde Sunrise, and Dating a Found Object.
Mercury’s axial tilt is about two hundredths of a degree, so the floors of its polar craters have never received direct sunlight and sit at a few tens of kelvin, while the equatorial surface reaches roughly seven hundred kelvin at noon. Radar-bright polar deposits identified in the 1990s are understood as water ice beneath a dark, volatile-rich lag, and such permanently shadowed regions act as cold traps that accumulate and preserve material indefinitely, disturbed only by slow micrometeorite gardening. Cold-trapped volatile films on a buried object are a reasonable extension of that physics, and they are genuinely fragile: species adsorbed at sixty kelvin are mobilised well below two hundred, so warming destroys exactly the record that makes a context-free object interpretable — which is why cryogenic sample return from such environments is treated as a thermal problem first and a chemistry problem second. Thermal operations on an airless body work as described: with no atmosphere to transport heat, radiative exchange between surfaces dominates, a vehicle in shadow can be heated strongly by infrared from a nearby sunlit cliff, and the temperature discontinuity across a shadow boundary is abrupt. Mercury’s three-to-two spin-orbit resonance gives a solar day of about one hundred and seventy-six Earth days and a terminator crossing the equator at roughly walking pace; and because the orbit is highly eccentric, near perihelion the planet’s orbital angular speed briefly exceeds its rotational angular speed, so at certain longitudes the Sun’s apparent motion reverses, producing a sunrise, a retreat and a second sunrise. The planet is contracting as it cools, producing lobate thrust scarps, some young enough to indicate ongoing tectonic activity and therefore seismicity and slope failure. On the object: iron-nickel meteorites are common, and concentric compositional banding can arise naturally in a small melt droplet solidifying inward in vacuum, with trace elements partitioning at the advancing front — a diffusion-limited process with a long laboratory literature. The dating methods are standard: galactic cosmic rays produce cosmogenic nuclides in metal at calculable rates, giving an exposure age that begins when an object comes within roughly a metre of the surface; solar-wind implantation samples the outermost nanometres and gives a much shallower, younger clock; solar-flare particle tracks and micrometeorite pit densities give further, cruder ones. Faces of the same object exposed for different durations will therefore record different ages, and the straightforward interpretation of a large discrepancy is overturning, most simply by a nearby impact whose own crater may since have been erased by gardening. The attempts described in review — reworking the shielding geometry, pushing the muon flux parameters, demanding blind recalibration and independent replication — are the normal and correct response of a committee to an inconvenient number. The epistemological position taken is the standard one: a single object without stratigraphic context supports measurement but not inference about origin.
Below Hearing
The mechanism: Balloon Infrasound Seismology at Venus, of the Cloud-Deck Environment, and of the Habitability Question.
The setting is accurate. At roughly fifty to fifty-five kilometres above the surface of Venus the pressure is about one Earth atmosphere and the temperature is that of a warm terrestrial afternoon, which makes that layer the most Earth-like environment in the solar system outside the Earth, with gravity at nine tenths of Earth’s. It would nonetheless kill an unprotected person promptly: the atmosphere is over ninety-six percent carbon dioxide, an asphyxiant and narcotic at that partial pressure, and the clouds are droplets of concentrated sulfuric acid, most aggressive around fifty kilometres. A nitrogen-oxygen mixture at the same conditions is roughly half the density of Venusian air, so breathable air is a lifting gas there and a crewed aerostat can float on its own habitable atmosphere — which makes loss of gas and loss of altitude the same failure, with descent raising temperature, softening polymer films and accelerating the loss. The atmosphere superrotates, circling the planet in four to five days against a solid-body rotation of two hundred and forty-three days, so a free-floating station circumnavigates Venus about every four and a half days, cannot station-keep, and steers only by changing altitude into a different wind. The stationary bow-shaped wave above Aphrodite Terra, some ten thousand kilometres across and holding position against the superrotating flow, was observed by the Akatsuki orbiter and is understood as a mountain-forced gravity wave.
On the seismology: Venus has no seismic network and the surface conditions of about four hundred and sixty-five degrees and ninety-two bars have so far limited landed operation to a couple of hours, while the planet’s nearly uniform and geologically young surface remains unexplained. Because the near-surface atmosphere is extraordinarily dense, around sixty-five kilograms per cubic metre, ground motion couples into acoustic energy far more efficiently than on Earth — by something like a factor of sixty — and infrasound from a quake reaches balloon altitudes in a few minutes. Balloon-borne infrasound detection of earthquakes has been demonstrated in Earth’s stratosphere and the Venus application is an actively studied mission concept. The central difficulty is equally real: atmospheric gravity waves, convection and the platform’s own motion produce pressure fluctuations of comparable amplitude and duration in the same band, and separating a vertically arriving acoustic signal from a horizontally propagating atmospheric one requires either spatially separated sensors or, as here, measurements at different altitudes compared against the sound-speed profile. Amplitudes of a few millipascals are the right order.
On the habitability argument, which the crew conducts accurately: the case for life in the clouds rests on the Earth-like pressure and temperature, abundant light, a long list of unexplained chemical anomalies including the still-disputed detection of phosphine and the century-old mystery of the ultraviolet absorber, the existence of terrestrial organisms that thrive at pH near zero, and the real if inefficient possibility of material transfer from Earth to Venus over geological time. The strongest objection is not heat or acid but water activity: concentrated sulfuric acid droplets have a water activity of the order of a few thousandths, while the lowest value at which any known terrestrial organism has been shown to metabolise is about 0.585 — roughly two orders of magnitude away, in a variable for which no adaptation is known, since water is the medium in which the chemistry happens. A secondary objection is that droplets settle out of the temperate layer within weeks, requiring a desiccated spore phase and a lofting cycle to close. The contamination point is also sound: forward contamination of the cloud deck by a crewed platform would be effectively impossible to exclude afterwards, which is one reason planetary-protection policy treats such a decision as irreversible.
One-way light time between Earth and Venus ranges from about two minutes near closest approach to roughly fifteen minutes at superior conjunction; the figures used here correspond to Venus on the far side of the Sun.
Dynamically New
The mechanism: Dynamically New Comets, Hypervolatile Sampling, and Surface Operations on an Active Nucleus.
A dynamically new comet is one making its first passage through the inner solar system after storage in the Oort cloud, where temperatures remain near twenty kelvin for the age of the solar system. Such objects therefore retain hypervolatiles — carbon monoxide, nitrogen, methane, argon — in their near-subsurface, which returning comets have long since lost from their outer layers, so first-passage material is genuinely unrepeatable: the volatile inventory is destroyed by the first perihelion and no second first passage exists. Carbon monoxide sublimates around twenty-five kelvin and drives activity at large heliocentric distances, which is why dynamically new comets are observed to be active well beyond the water-ice line. Nucleus properties are drawn from the Rosetta mission’s characterisation of 67P/Churyumov–Gerasimenko: a bilobed body a few kilometres across, bulk density a little over half that of water, porosity of around seventy percent, extremely low tensile strength, and a very dark surface with an albedo of a few percent because of a carbon-rich dust mantle. Escape velocity on such a body is of order one metre per second and surface gravity is around a ten-thousandth of Earth’s, so a suited person weighs a few grams, walking is not possible and all movement is by line. Gas drag from a nearby active area can readily exceed that weight and lift an unsecured person; dust is continuously lofted and much of it does not return. Pit formation by subsurface sublimation and roof collapse was directly observed at 67P, as were cliff collapses exposing fresh volatile-rich material that becomes active within hours to days and is eroded away within months — a genuine and short-lived window onto unprocessed stratigraphy. The thermal processing front migrates downward over weeks, so depth below that front is the operative sampling criterion. The onset of activity within minutes of local sunrise on a freshly exposed face is consistent with observed diurnal activity cycles. The coma of an active comet, while an excellent vacuum by laboratory standards, is optically thick enough in dust to obscure the stars and to produce a diffuse illuminated sky, and the soft terminator follows from the same scattering. Cryogenic sample return at thirty kelvin is beyond present practice but is the stated goal of proposed comet nucleus sample return missions, and deliberately curating most of a returned allocation for future instruments is standard practice with the Apollo and Hayabusa collections. Roughly a tenth of dynamically new comets are observed to disintegrate at or near perihelion. Finally, the delivery argument is as stated: comets contributed water, nitrogen species and complex organics to the early Earth, these are the same molecules rather than analogues of them, and the inference that they brought ingredients rather than life is the mainstream position.
Everything Verifies
The mechanism: Silent Multi-Bit Memory Corruption by Galactic Cosmic Rays, and of Human Operations at Callisto.
The failure mechanism is real and is a recognised hazard rather than an invention. Galactic cosmic rays are mostly protons, with about one percent heavy nuclei fully stripped of electrons, and that heavy component dominates both the single-event effects in electronics and the biological risk; measured deep-space dose rates during the Mars Science Laboratory cruise were about 1.8 mSv per day. Moderate aluminium shielding can raise the biological dose by fragmenting incoming nuclei into secondary showers, so hydrogen-rich materials are preferred. Memory upsets are routine and are handled by error-correcting codes and by continuous scrubbing. The danger in this story is also standard knowledge in the radiation-effects community: as cells shrink, one ion track can upset several physically adjacent cells, and if those belong to the same logical word the code can mis-correct onto a valid codeword that is not the stored value. The defence is physical bit interleaving, reducing it for density is a genuine temptation invisible at sea level, and qualifying such a part in a proton beam rather than with heavy ions would under-sample the multi-bit regime. A scrubber that rewrites a mis-corrected word, plus integrity hashes recomputed each generation instead of compared against an immutable launch reference, is the terrestrial failure called silent data corruption. On the biology side, heavy-ion exposure produces measurable deficits in attention and in competitive recall in animal models, while the human evidence remains thin, which is why both branches of the story’s fork are allowed to be true at once. Five-dimensional optical storage in fused silica is real, is written by femtosecond laser pulses as birefringent nanostructures, is read through crossed polarisers under magnification, and is immune to this failure because nothing is stored as charge. The Jovian system is as described. Radiation at Europa is of order hundreds of rem per day and at Ganymede several rem per day, while Callisto, orbiting beyond the worst of the trapped belts, receives roughly one hundredth of a rem per day, which is the reason every serious study of a crewed Jovian outpost has chosen it. Callisto is tidally locked, so Jupiter stands fixed in the sky of the sub-Jovian hemisphere at about four and a half degrees across — nine times the width of the Moon from Earth — rotating visibly in place every ten hours while never changing position, and at full phase it supplies roughly an order of magnitude more light than a full Moon on Earth, enough to fill shadows that would be black anywhere else. Sunlight at Jupiter is about one twenty-seventh of its intensity at Earth. Surface gravity is about an eighth of Earth’s, the day is sixteen and a half Earth days, and the surface is a dark sublimation lag deposit over dirty ice, with bright ice exposed on slopes and with eroded ice knobs and spires reaching some tens of metres, observed by Galileo. Crater density on Callisto has saturated, large old craters have relaxed into flat palimpsests, and Valhalla is a multi-ring structure spanning several thousand kilometres. Landing is entirely propulsive with no atmosphere to help, and ejected dust departs on near-ballistic trajectories rather than forming a settling cloud. Heat leaking from a structure into ground ice causes sublimation and differential settling, which is an acknowledged design problem for icy-moon installations. The one-way light time from Jupiter to Earth is roughly three quarters of an hour, which is the honest argument for having people on site, alongside the other argument, which is also honest and is about photographs.
Lift
The mechanism: Human Flight on Titan.
Titan’s surface conditions are as described: a nitrogen atmosphere at about one and a half bars — higher than Earth’s sea-level pressure — at a temperature near ninety-four kelvin, with a surface gravity of roughly one seventh of Earth’s and an atmospheric density some four to five times that of air at sea level. Because the external pressure exceeds Earth’s, a surface suit does not need to be a pressure garment at all: it needs breathing gas, a sealed hood and heavy insulation, so a flexible drysuit with a rebreather is the appropriate design, and this is the standard conclusion in the literature on crewed Titan operations. Cold, not vacuum, is the governing hazard. Vacuum is an excellent insulator and radiative loss is slow, whereas a dense cryogenic atmosphere removes heat by conduction and convection at rates far exceeding anything experienced in space, making thermal management the limiting constraint on any surface excursion and making metabolic heat from exertion a genuine asset. Human-powered flight is a direct consequence of the numbers: lift scales with atmospheric density and wing area and with the square of airspeed, while weight scales with gravity, so the lift-to-weight ratio available for a given wing at a given speed is more than thirty times the terrestrial value, and a suited adult can be supported by a few square metres of wing at a flying speed of about four metres per second. This conclusion is well established in the planetary science literature on Titan and is frequently cited as the most striking consequence of the moon’s environment. Descent in the event of exhaustion is gentle, with sink rates of a couple of metres per second, so the activity is intrinsically low-risk over land. Sound propagates well in the dense atmosphere, carrying unaided speech between people, and because the speed of sound is roughly a hundred and ninety metres per second — less than half the terrestrial value — vocal tract resonances shift downward and human voices are lowered in pitch, an effect opposite to that of breathing helium. Illumination at the surface is of order a thousandth of terrestrial daylight, diffused by organic haze into a shadowless orange-brown light in which neither the Sun nor Saturn is visible. Titan’s day is just under sixteen Earth days. The northern seas, including Ligeia Mare, are liquid methane and ethane with dissolved nitrogen, and radar observations show them to be extraordinarily smooth, with waves of at most a centimetre or so, producing near-specular reflection. Equatorial longitudinal dunes of dark organic sand run for hundreds of kilometres with heights of around a hundred metres. Methane rain is rare but occurs, with drop diameters up to roughly nine millimetres and terminal velocities near one and a half metres per second — slow enough to follow individually by eye — and the shallow pools it leaves evaporate over subsequent months while continuous haze fallout settles onto them. Immersion in liquid methane at ninety-four kelvin would exceed any suit’s thermal capacity within minutes, which is the basis of the prohibition on flight over liquid.
Vapour Pressure
The mechanism: Pluto’s Collapsing Atmosphere, Sputnik Planitia, the Charon Geometry, and Life Support from the Surface.
Pluto’s atmosphere is in vapour-pressure equilibrium with the nitrogen ice on its surface, so its pressure is an exponential function of surface temperature: a change of one kelvin alters the pressure by tens of percent. Pluto passed perihelion at about thirty astronomical units in 1989 and reaches aphelion near forty-nine in 2114, with insolation falling as the inverse square of distance, and the orbital period is two hundred and forty-eight years. Stellar occultation measurements show the atmosphere’s pressure roughly tripled between 1988 and 2015 despite the increasing distance, owing to the thermal inertia of the nitrogen glacier, and current models predict a peak followed by a substantial decline over the following decades, with large but model-dependent collapse toward aphelion — the pressures used here are illustrative of that family of predictions rather than any single published curve. Surface pressure at the time of the New Horizons encounter was of order one pascal, which is a hard vacuum by laboratory standards yet is spread over a deep enough column to make aerocapture a serious engineering proposition, and the loss of that capability as the atmosphere freezes out is a genuine consequence. Surface temperature is around forty kelvin, gravity is about one sixteenth of Earth’s, and sunlight is roughly a thousandth of terrestrial daylight — comparable to civil twilight and entirely adequate for work. The atmospheric haze is organic, arranged in some twenty discernible layers to altitudes of over two hundred kilometres, and scatters blue, so Pluto has blue twilight; haze particles settle continuously and darken low ground. Sputnik Planitia is a basin of nitrogen ice roughly a thousand kilometres across whose surface is free of impact craters because it is renewed by solid-state convection in cells of twenty to thirty kilometres, overturning on timescales of order half a million years, with water-ice mountain blocks at its margins behaving as floating fragments; slow marginal motion of such a glacier against its shore is expected. Pluto and Charon are mutually tidally locked with an orbital and rotational period of six point four Earth days and a separation of about nineteen and a half thousand kilometres, so Charon subtends roughly three and a half degrees — about seven times the Moon’s apparent diameter from Earth — and hangs motionless in the sky of the sub-Charon hemisphere while remaining permanently invisible from the other. The reddish deposit at Charon’s northern pole is attributed to methane escaping from Pluto, cold-trapping at Charon’s winter pole and being processed by ultraviolet light into tholins. In-situ life support from local volatiles follows directly: nitrogen from the surface ice, oxygen by electrolysis of water ice, which at these temperatures has the mechanical character of rock. Sourdough cultures are indefinitely maintainable, acquire their microbial population from their immediate human environment, can be dried and rehydrated after long storage, and behave differently in low gravity because dough rise is a buoyancy-driven process.
