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An Ocean is a Snowflake, Four Billion Miles Away

Written by John Barnes

Illustrated by Jennifer Miller

Thorby had kept up his resistance training, but he'd been on Boreas for most of a year so he'd worried about agravitic muscular dystrophy. You could never quite trust a gym centrifuge, or the record-keeping software, or most of all your own laziness. You might set things too low, lie to the records, anything to not be quite so sore and stiff for just a couple days, or to have a few days of no aches, and before you knew it you hadn't actually worked out in a month, and you'd be falling down weak at your next port. He'd missed recording the first calcium bombardment of Venus from ground level for that very reason, not working out while he'd been in the orbital station for three months before.

People always said you could make it back by working out in the high gravity on the ships between the worlds, but the ships boosted at a gee and a half until they started braking at four gee, so you spent all your time lying down or doing gentle stretches at best, and most trips weren't long enough anyway. And besides this had been less of a voyage and more of a hop; Boreas was very close to Mars now.

The comfortable grip of his feet on the train station platform, confirming that he was truly ready for Mars's real gravity, was as acute a pleasure as the clean thinness of bioprocessed air lightly stained with smells of coffee, frying meat, lubricant, and fresh plastic, as much as the pink late afternoon light flooding the train station, as much as the restless waves and murmurs of crowd noise.

He could have laughed out loud at how good it felt to be in his skin, standing on the platform at Olympus Station, a throng of eager hikers, sailplaners, and mountaineers all around him, the whole scene turned warm and sentimental by the pink light pouring in through the immense dome that arched above them.

It had been a decade since he'd been on Mars, a planet like the rest of the solar system: a place he always came back to, because he never went home.

"Thorby!" Léoa emerged from the crowd, saw him, and waved; he walked toward her slowly, still relishing the feel of having good ground legs.

"So do I look like me?" she asked. "Did you know that back in the protomedia days, when they had recording tech but things hadn't fused yet, that it was a cliché that people always looked better than their pictures?"

"I've mined protomedia for images and sounds too. My theory about that is that you couldn't get laid by telling the picture that it was the better-looking one."

"You're an evil cynic. Pbbbt." Even sticking her tongue out, she was beautiful.

So was he. All documentarians had to be, the market insisted.

"I never used pixel edit on myself," she said. He wasn't sure if she sounded proud or they were just having a professional discussion. "So screen-me does look unusually like real-me. I'll do a docu about the way people react to that, someday. Want to get a drink, maybe a meal? It's hours till our train." Without waiting for him to say anything, she turned and walked away.

Hurrying to catch up beside her, he called, "Baggins, follow," over his shoulder. His porter robot trailed after them, carrying Thorby's stack of packed boxes. Everything physical he owned still fit into a cube with sides shorter than his height. "Did you have a good trip in?" he asked her.

"For me it's always a great one. I've been here for six Martian seasons, three Earth years, and I'll never be one of the ones that shutters the window to concentrate on work. I came in from Airy Zero City via the APK&T."

"Uh, it's been a long time since I've been on Mars, is that a railroad?"

"Oh, it's a railroad—the grandest on the planet. The Airy Zero City-Polar Cap-Korolev-and-Tharsis. The one that tourists take if they only have one day on Mars. Also the one we'll be taking up to Crater Korolev for jump-off. Among many other things it runs around the edge of the northern ice cap. Strange to think it won't be long before it stops running. They're just going to leave it for the divers, you know, and maybe as a spread path for some of the seabed fauna. More to be lost."

"If we're going to start bickering," Thorby said, smiling, "shouldn't we be recording it? Or will that draw too much attention?"

"Not on Mars. It's a tourist planet—pretending celebs aren't there is de rigueur. And you don't look much like your teenaged pictures anymore."

"They were mostly in a spacesuit where you couldn't see my face anyway," he pointed out. "And I don't use my face in my docus. I was thinking mainly about you."

"Pbbbt. I never was much of a celeb. There won't be fifty people in all these hundreds who have ever seen any of my work. So the short answer is, if anything, it might be some worthwhile free publicity to do the interview while we walk through here. I'll bring out my stalkers." She whistled, a soft high-pitched phweet!—toooeee... wheep.

A hatch opened on the porter humming along at her heels. A metal head on a single stalk popped up. The stalker hopped out and raced ahead of them to get a front view. Four more stalkers leaped out like toy mouse heads roller-skating on pogo sticks, zipping and bounding to form a rough, open semicircle around Thorby and Léoa, pointing their recording cameras back at the two people, and using their forward sensing to zigzag swiftly and silently around everything else.

"I intend to look sincere and charming," Léoa said. "Do your best to look philosophical and profound."

"I'll try. It might come out bewildered and constipated."

She was nice enough to laugh, which was nicer than he was expecting. They descended the wide steps onto the broad terrace, far down the low, northwest side of the dome, and took a table near the dome surface, looking northwestward from Mount Olympus across the flat, ancient lava lake and into the broken, volcanic badlands called sulci beyond it. "Our ancestors would have found a lot of what we do utterly mad," Léoa said, "so I suppose it's comforting that we can find one thing they did explicable."

"You're trying to get me to say something for the documentary."

"You're spoiling the spontaneity. Of course I notice you do that all the time in your own documentaries."

"I do. Spontaneity is overrated when you're covering big explosions and collisions. They only happen once, so you have to get them right, and that means looking in the right place at the right time, and that means a ton of prep."

"All right, well, have you had enough time to prepare to talk about something the ancestors would consider insane? What do you think about putting a train station on top of the highest mountain in the solar system?"

"Where else would you put it? People who want to climb the mountain still can, and then they can take the train home. People who just want the view just take the train both ways. And once it starts to snow seriously around here, the skiing is going to be amazing. So of course there's a train station here. They put it here to attract trains, the way Earth people put out birdfeeders to attract birds."

She nodded solemnly and he realized she was doing a reaction shot on him, showing her sincerity and trust. He looked away, out through the dome.

"You're getting lost in the sky," Léoa said.

"I like the pink skies here."

"Doesn't it bother you that there will probably only be a thousand or so more of those?"

"Not any more than it bothers me that I've missed billions of them before I was born."

"What about the people who will never see it?"

"They'll get to surf the new ocean, and stretch out on the beaches that all the dust washing out of the sulci and down the canyons will form. They'll love that, in their moments. In my moment, I'm relishing a late afternoon pink sky."

The stalker in the center was spinning back and forth, pointing its camera at each of them in turn; so now it was a ping-pong match. They did more verbal sparring and genned more quotes and reactions, ensuring they'd both have plenty to work with when the coproject went to edit. After a while they ordered dinner, and she stopped fishing for him to confess to imperialism or vandalism or whatever she was going to call it.

She told her Stalker Number Three to silhouette him against the darkening sky and the landscape far below. The little robot leaped up, extended its pencil-thin support to a bit over two meters, and silently crept around to shoot slightly down on Thorby and get the horizon into the picture.

When Boreas rose in the northwest, covering much of the sky, they both said "more profounder versions of what we already said," as Léoa put it, while the stalkers recorded them with their back to the dome wall. Léoa had her stalkers stand tall, extending till they were about three meters high, to catch the brilliant white light that the huge comet cast into the sulci below; Thorby positioned his low, to silhouette them against the comet head itself. The huge station mezzanine around them, in the brilliant bluish-white light, looked like some harsh early photograph with artificial lighting.

Over coffee and dessert, they watched the fast-rising comet swim through the northern constellations like a vast snake coiling around Cepheus and the Bears before diving over the northeast horizon, making a vivid arc different from that of anything else in the heavens. Finally it was late and they went to their rooms at the station hotel for the night. Thorby managed not to say anything about liking to see stuff smashed up, and she avoided saying she really preferred bare, dead rock and sand to forests and meadows, so the first day was a tie.

****

 They got off at Korolev Station, on the south side of the crater, pulled on Mars suits, loaded the porters, and walked out past the stupa that was another of the most-photographed places in the solar system.

Crater Korolev was as far north on Mars as Novaya Zemlya on Earth, nearly circular, about seventy kilometers across, with sharply reared crater walls all around. It was a natural snow trap, gathering both water ice and dry ice in mixtures and layers.

In a midmorning of Martian spring, the crater floor far below them had its own weather, gas geysers spraying snow, explosive sublimations that sent ground blizzards shooting out radially from suddenly exposed snowfields, and an occasional booming flash-and-crack between the whorls of fog that slithered just above the snow, almost a kilometer below the observation point behind the stupa. Monks in orange Mars suits, on their way to and from the long staircases that zigzagged from the stupa down to another stupa on the crater floor, passed between their stalkers, even less interested in the stalkers than the stalkers were in them.

"This place makes a lot of lists of scenic wonders," Léoa said. She knelt at the meter-high shrine that interrupted the rails of the observation platform, palms together in the ancient prayer gesture. The stalkers closed in on her.

He did the same, to avoid her stalkers' recording him being disrespectful.

When Thorby and Léoa stood, and looked again across the stormy snowfields of Korolev Crater, the stalkers leaped up on the railing like an abstract sculpture of birds on a wire, balancing easily with their gyros. Thorby and Léoa de-opaqued their helmets completely and turned on collar lights. "It doesn't bother you," she asked, "that these snow fields were here before the first human wandered across the African plain?"

"No," he said. "After all, the protons and electrons in the snow were probably in existence shortly after the Big Bang. Everything is made of bits of something older. Everything that begins means something ends. I like to take pictures of the moment when that happens. A day will come when we walk by Lake Korolev and admire the slow waves rolling across its deep blue surface, and then another day will come when this stupa stands on one of the islands that ring Korolev Atoll, and very much within our lifetime, unless we are unlucky, this will be an interesting structure at the bottom of the Boreal Ocean. I hope to see them all; life is potential and possibility."

"That was very preachy," she said, "and you kind of intoned. Do you want to try it again?"

"Not really. Intoning feels right when I'm serious. I like things that will happen once, then never again. That's what my problem is with the animators that make their perfect simulations; they never take a chance on not getting what they're after. Be sure to use that. Let's get some animators good and angry."

"They don't get angry," she said sadly. "Nothing's real to them."

He shrugged. "Reality is just a marketing trophy anyway. Twenty thousand years from now, if people want to walk around on a dry, thin-aired, cold Mars, they'll be able to do it, and it will look so much like this that even a trained areologist won't see the difference. Or if they want to watch the disassembly of Boreas a hundred times, and have every time be as subtly different as two different Tuesdays, they'll be able to. Your recording of what was, and my recording of how it changed, will just be two more versions, the ones with that odd word 'real' attached."

"Attached validly. If reality doesn't matter, why do animators try to fake their way into having their work labeled 'real' all the time? It's the only thing they do that makes me really angry."

"Me too." He could think of nothing else to add. "Catch the gliderail?"

In the half-hour zip around to the north side viewing station, they sat on the top, outside deck. Their stalkers shot them with the crater in the background. It was noon now, and the early spring sun was still low in the sky to the south.

On firm ground, in a Mars suit with robot porters to do all the carrying, a human being can cover about a hundred kilometers in a day without difficulty. Since the country they were crossing was ancient sea bottom (that was the point of everything, really), it would be flat and hard for the next couple of hundred kilometers before the Sand Sea. They could have just taken a hop-rocket to some point in the vast plain, claimed to have walked there, recorded their conversation, and then hopped another hundred kilometers or so to the edge of the Sand Sea, but they were the two most prominent documentarians of the realist movement.

Visually it was monotonous. They had planned to use the long walk to spar for quotes, but there was little to say to each other. Léoa documented places that were about to be destroyed in the Great Blooming; Thorby recorded the BEREs, Big Energy Release Events, the vast crashes and explosions that marked humanity's project of turning the solar system into a park and zoo. They were realist-purists, using only what a camera or a mike could record from the real world. Unable to do anything except disagree or agree completely, they tried arguing about whether a terraformed planet can have wilderness, since the life on it was brought there and the world shaped for it, and about whether it was masculine to like to see things smashed and feminine to like to see things protected, and they agreed that animation had no place in docu, all in the first hour.

For a while she fished for him to tell stories about his brief moment of fame, as the teenager who rode his bicycle around a comet, but he didn't feel like telling that story during that hike, though he did promise to tell it eventually. It wasn't that he minded, it was only that the good-parts version came down to no more than four or five sentences for anyone else, and to inchoate, averbal images for Thorby.

By noon the first day, there was nothing to do but walk and look for something worth recording, or an argument worth having. They walked two more days.

****

 The Sand Sea was no more conversational, but it was beautiful: an erg that stretched to the horizon, dune after dune in interlocking serpentines stretching for hundreds of kilometers in all directions. From orbit the regularity of the pattern of dune crests was remarkable, but from the dune crests, where they skied, it was busy and confusing like a choppy sea. Down between the dunes it was just piles of sand reaching to the sky on all sides.

They hadn't spoken in hours. Léoa didn't even ask him if he felt sad that all this would be converted to a mud flat and then drowned under three kilometers of water. He couldn't work up the energy to needle her about protecting a pile of dust the size of France, so that future generations could also visit a pile of dust the size of France.

They went slowly for the last day, as Léoa got visuals of the Sand Sea. She had built her reputation on doomed landscapes; this would be the biggest to date.

Thorby was sitting on top of one of the immense dunes, watching the sunset and talking his notes to one of his stalkers, planning the shooting of the Boreas-pass above the North Pole. He felt a low vibration, and his suit exmike, which had only supplied a soft whisper for days, reverberated with deep bass notes, something between a tuba and a bell, or a choir of mountains.

The dune under him heaved like an ocean wave waking from a long sleep, and he tumbled over, rolling and sliding in a bewildering blur of dust and sky, halfway down the western, windward face before sliding to a halt. The slipping dust piled around him, starting to pin him to the ground.

He pushed up to his feet, and stepping high, climbed back up the dune. It was more than a minute, while the pure tones of the bass notes in his exmike became a continuous thunder of tympani, before he struggled back to the top. The sun was less than a fingerwidth above the short horizon, and the light would disappear in minutes, the smaller solar disk and short horizon of Mars reducing twilight to an instant.

The thunder was still loud, so he clicked up the volume on his radio. "Are you all right?"

"Far as I can tell. It buried me to my waist but I got out." He picked out Léoa, climbing the leeward slope far below. "Booming sands," she said. "One of the last times they'll ever do it. The resonance trips off more distant dunes, one dune triggering another by the sounds, till all the dunes with those frequencies have avalanched and added to the din. There's a scientist I met who sowed microphones all over the polar sea and he could show you maps of how the booming would spread from dune to dune, all over the Sand Sea in a couple of hours. And all that will be silent forever."

"Silent as the Boreal Ocean is now," he said, mindful that their recording mikes were still on and so was the sparring match. All round them, stalkers were finding their way back to the surface, usually stalk first so that they rose like slim reeds from the ground until they suddenly flipped over, spun to clear the dust from their scoop shaped audio pickups, and resumed hopping through the sand like mouse heads on pogo sticks, normal as ever. "There was a time to hear the sands, and there will be a time to hear the waves. And in between there's going to be some of the grandest smashing you ever saw."

She must not have had a good reply, or perhaps she just didn't want to reply to his intoning again, because she got back to her setup, and he got back to his.

The Mars suits shed the fine dust constantly, so that Léoa seemed to smolder and then to trail long streaks as the wind shifted during the few seconds of twilight. They finished under the stalkers' work lights, and lay down to wait on the soft lee of the dune, safe now because it had just avalanched.

"Thorby," she said, "this is not turning into anything that will make either of us famous."

He hunched his shoulders, shaping the fine sand under him. "You're right," he said. "It's not."

"You've already been famous."

"It's one of those things you can't experience while it's happening," he said, "like seeing yourself across a crowded room. Not all that it's cracked up to be. I like making docus and I like selling them, so that kind of 'where is he now' fame doesn't hurt, and it's far enough in the past so I mostly get left alone." He watched Phobos, far south in the sky; from these far northern latitudes you never saw it full, always as a lumpy sort of half-moon.

"If a model or a musician had taken a tumble in booming sands it would sell systemwide, but if we got stranded out here and you killed and ate me to survive, it would barely show up. Docus are what, half a percent of the market? There's not even a market in pirating them." Léoa sighed. "I was just thinking that the mainstream celeb channels haven't even mentioned that the two leading documentarians of the realist-purist movement are here to record the biggest event of the next few hundred years of the Great Blooming, the re-creation of the Boreal Ocean. Not even to mention that we've always feuded and we purportedly hate each other. Not even to do one of those 'Will they reconcile and have sex?' stories they like so much. Not even to mention that one of us is the teenager who took the longest bicycle ride in history. Yet two years ago they covered the fad for learning to hand-read, and a couple guys in the retro movement that produced written books—can you believe it, written books, just code, that stuff people used to hand-read—and they covered a blacksmith last year, but docus are so dead, they didn't bother with us."

"We're not dead enough. Gone but not long enough or completely enough to be a novelty." He tried to decide whether he could actually see Phobos crawling along eastward, down by the equator, and decided he could. "Maybe we should have the blacksmith build us chariots, and race each other, and do a documentary about that."

"Maybe." The scratchy sound in her radio puzzled him till he saw her rolling over; she was looking for a comfortable position on the dune, and he was hearing her Mars suit pushing dust away.

"Hey," he said. "Since you've been trying to get me to miss something, I just noticed something I will miss. Phobos. I like the way it looks from this far north."

"Well, I'm glad something can touch your heart. I'd have thought you were excited about getting to see it fall."

"It won't be much of a show. Phobos'll be busted to gravel from all the impacts as it comes down through the rings, so it won't really be a BERE, just a month-long high point in the spectacular meteor shower that will go on for fifteen Mars-years or so. I wasn't even going to bother to shoot it. But what it is right now—I never realized it's always a half-moon up here in the far north, because it's so close to the equator and so low in orbit, and besides, it's fun just to watch it, because it's so low it orbits really fast, and I'm thinking I can see it move."

"I think I can too." She commanded her stalkers to set up and record the view of Phobos, and then to get the two of them with Phobos behind them as they sat on a dune. "Those shots will be beautiful; so sad though that stories about Great Blooming projects are about as popular as public comment requests by the Global Desalination Authority."

He shrugged, hoping it would show up on the stalker's cameras. "Post scarcity economy, very long life spans, all that. Everything to do and nothing matters. Story of everyone's life. Have you thought about doing anything other than docus?"

"I try not to. I want to get the Great Blooming recorded, even if I call it the Great Vandalism or Bio-Stuff Imperialism. Somebody has to stand up for rocks, ice, and vacuum."

"Rocks make okay friends. They're dependable and loyal."

"I wish somebody wanted to watch us talking to each other," Léoa said. "About all this. About Mars and about the Blooming and all that stuff. I almost wouldn't care what we had to say, or how things came out, if somebody would just find us interesting enough to listen. You know what I mean."

"Yeah." Thorby didn't really feel that way himself but he often didn't know what he felt at all, so he might as well agree.

They began final checkout just a few minutes before Boreas's first aerobraking pass. The stalkers were self-maintaining, and they were already in place, but it felt wrong to just assume everything would work.

"This will be one of your last views of your home," Léoa said. "How do you feel about that?"

He turned toward her, flipped the opaquing on his helmet to zero, and turned up the collar lights, so that his face would be as visible as possible, since this was an answer he knew he needed to get right. Already the northern horizon was glowing with Boreas-dawn. "Boreas is where I grew up, as much as I ever did, but that doesn't make it home," he said. "First of all when I lived there you couldn't walk on most of it, anyway, and they weren't going to let a little boy put on a suit and go play outside. When I went back four weeks ago, all that melting and vaporizing that went on while Boreas worked its way down to the lower system had erased even the little bit of landscape I did know; I couldn't even find Cookie Crumb Hill on radar and thermal imaging, and anyway if I'd found it, it's so dark down there now, with all the fog and grit flying around, that I doubt I could have gotten pictures that penetrated more than twenty meters into the mess. The Boreas I knew when I was a kid, way out beyond Neptune, is more than a decade gone; it's nothing like it was. Nothing at all."

He was crabbier in his tone than he had meant to be, irritated by her question because he'd blown half his share of the budget to buy passage to Boreas so that he could come back with the seven scientists who were the last evacuated from the iceball's surface, and what he'd gotten had been some lackluster interviews that he could as easily have done a year before or a year after. Furthermore, since the station had not had windows, he could have done them somewhere more pleasant. He had also acquired some pictures of the fog-and-grit mix that now shrouded what was left of the old surface. (Most of the old surface, of course, now was fog and grit).

As Boreas came in over the North Pole, it would swing low enough for atmospheric drag, which, combined with the gravitational drag from coming in an "inverse slingshot" trajectory, should put it into a very eccentric, long orbit around Mars. Doing this with a big natural ball of mixed water ice, carbon dioxide, and frozen methane, with a silica-grit center, was so uncertain a process that the major goals for the project began with "1. avoid impact by Boreas, 2. avoid escape by Boreas."

But if all went well, nudgers and roasters would then be installed on Mars's new huge artificial moon, with the objective of parking it in a nearly circular retrograde orbit below Phobos, well inside Mars's Roche limit, so that over a few years, Boreas would break up and form a complex of rings. The billions of bits of it, dragged and shredded by the planet's rotation, would then gradually spiral in across twenty years, creating a spectacular continual meteor shower in the plane of the ring, a carbon dioxide/methane atmosphere at about a bar of pressure, and, as water vapor snowed down, then melted, then rained and ran to the lower parts of the planet, a new ocean in the bed of the dry-for-a-billion-years Boreal Ocean.

The comet's pass would light the sky for many hours, but its actual brush with the atmosphere would last less than three minutes. Thorby and Léoa intended to be directly underneath it when that happened.

"Did you leave anything on Boreas, a memento to be vaporized onto Mars?" she asked.

He started to say, "No."

She picked up her walking stick and knocked off the head of one of his stalkers.

Startled speechless for an instant, he didn't speak or move till she whacked the second one so hard that its head flew in pieces into the sand.

"What are you—"

"Destroying your stalkers." Her voice was perfectly calm and pleasant as she whacked another stalker hard enough to break its stem in half, then drove the tip of her stick down on its head. "You won't have a record of this. And mine will only be recording your face and appearance. You've lost."

He thought lost what? for an instant, and then he wanted to rush to see if Number Four stalker, which had been with him for twenty-five years, was all right because it was crushed and he couldn't help thinking of it as "hurt," and then he wanted to scream why?

The landscape became brighter than day, brighter than Earth lightning, not at all like the Boreas-dawn they had been expecting. A great light flashed out of the north, and a breath later a white, glowing pillar pushed up into the sky. They froze, staring, for some indefinite time; his surviving stalkers, and all of hers, rotated to face the light, like clockwork sunflowers.

Thorby heard his voice saying, "We'll need to run, south, now, as fast as we can, I don't think we'll make it."

"Must have been a big fragment far out from the main body," Léoa said. "How far away do you think—"

"Maybe up close to the pole if we're lucky. Come on," he said, "whistle everything into the porters. Skis on. Run."

 Two of his stalkers had not been destroyed, and they leaped into his porter at his emergency call. "Skis and poles," he told the porter, and it ejected them; he stepped onto the skis, free-heelers designed for covering ground and moving on the slick dust, and hoped his few hours practice at a comfortable pace in the last day would be enough to let him go fast now.

"Baggins, follow, absolute." Now his porter would try to stay within two meters of his transponder, catching up when it fell behind, until it ran out of power or was destroyed. If he lost it, he might have to walk hungry for a while, but the northern stations were only a couple of days to reach. His Mars suit batteries were good for a week or more; the suit extracted water and air; he just had to hope he wouldn't need the first aid kit, but it was too heavy to strap onto the suit.

The great blue-white welding-arc pillar had cooled to orange-white, and the main body of Boreas, rising right on schedule, stood behind it as a reflector. The light at Thorby's back was brighter than noonday equatorial sun on Earth, much brighter than any sun Mars had ever seen, and the blazing face of Boreas, a quarter of the sky, spread the light with eerie evenness, as if the whole world were under too-bright fluorescent light.

He hurled himself along the windward side of the south-tending dune crest, using the skating technique he'd learned on Earth snow and practiced on frozen methane beds on Triton; his pushing ski flew out behind him, turning behind the lead ski to give extra push, then reach as far in front of him as possible, kicking and reaching as far as he could. On the slick, small-round-particle sand of the ridge top, in the low gravity, he might have been averaging as much as twenty kilometers per hour.

But the blast front from the impact was coming at them at the local speed of sound, 755 kilometers per hour, and though that was only 2/3 as fast as Mach 1 in warm, thick, breathable air, it was more than fast enough to overtake them in a half hour or less. At best the impact might have been four hundred kilometers away, but it was almost surely closer.

He glanced back. Léoa skied swiftly after him, perhaps even gaining ground. The light of the blazing pillar was dimmer, turning orange, and his long shadow, racing in front of him, was mostly cast by the dirt-filtered light of the Boreas-dawn. He wasn't sure whether Boreas would stay in the sky till the sun came up, but by then it would all be decided anyway.

"Thorby."

"Yeah."

"I've had it look for shelter, read me some directions, and project a sim so I'm sure, and there's a spot that's probably safe close to here. This dune crest will fork in about a kilometer. Take the left fork, two more kilometers, and we'll be behind a crater wall from the blast."

"Good thinking, thanks." He pushed harder, clicking his tongue control for an oxy boost. His Mars suit increased the pressure and switched to pure oxygen; his pace was far above sustainable, but either he made this next three kilometers or he didn't.

Léoa had destroyed his recording setup. He'd known she deplored his entire career of recording BEREs—Big Energy Release Events—at least as much as she disliked the whole idea of the Great Blooming, but he'd had no idea she would actually hash the joint project just to stop him from doing it. So his judgment about people was even worse than he'd thought it was. They had been colleagues and (he'd thought) friendly rivals for decades, and he hadn't seen it coming.

He kept pushing hard, remembering that he was pouring so much oxygen into his bloodstream that he had to keep his muscles working hard, or hyperventilate. His skis flew around him, reached out to the front, whipped back, turned, lifted, flew out around him, and he concentrated on picking his path in the shifting light and staying comfortably level and in control; in the low Martian gravity, with the close horizon that didn't reveal parallax motion very well to eyes evolved for Earth, it was far too easy to start to bounce; your hips and knees could easily eat a third of your energy in useless vertical motion.

The leeward side of a dune crest is the one that avalanches, so he stayed to the right, windward side, but he couldn't afford to miss the saddle-and-fork when it came, so he had to keep his head above the crest. He heard only the hiss of his breath and the squeal of his skis on the sand; the boiling column from the impact, now a dull angry red, and the quarter-of-the-sky circle of the comet now almost directly overhead were eerie in their silence. He kept his gaze level and straight out to the horizon, let his legs and gut swing him forward, kept the swinging as vertical as he could, turning only the ski, never the hip, hoping this was right and he was remembering how to do it, unable to know if he was moving fast enough through the apparently endless erg.

He had just found the fork and made the left turn, glancing back to check on Léoa. She seemed to be struggling and falling a little behind, so he slowed, wondering if it would be all right to tell her she was bouncing and burning unnecessary energy.

The whole top five meters of the dune crest under her slid down to the leeward in one vast avalanche. For one instant he thought, but how can that be, I just skied it myself and I'm heavier. the ground fell away beneath him in shattering thunder as the whole dune slumped leeward.

Of course, how did I miss that? In the Martian atmosphere, a cold thin scatter of heavy CO2 molecules, sound is much slower than it is in anything human beings can breathe; anyone learns that after the first few times a hiking buddy's radio has exmike sound in the background, and it seems to be forever before your own exmike picks it up. But the basalts of the old Martian sea floor are solid, dense, cold, and rigid to a great depth; seismic waves are faster than they are elsewhere.

He thought that as he flipped over once, as if he were working up the voiceover for his last docu. Definitely for his last docu.

In the low gravity, it was a long way to the bottom of the dune. Sand poured and rumbled all around him, and his exmike choked back the terrible din of thousands of dunes, as the booming erg was all shaken at once by the S-waves running through the rock below it, setting up countless resonances, triggering more