Titan

BOOK FIVE Extravehicular Activity A.D. 2015 — A.D. 2016

In 1990 its controllers had had Voyager One look back and take one last picture sequence before shutting down its camera.

Voyager swivelled its instrument platform and shot a panoramic view of sixty images, encompassing in a single sweep every planet from Neptune, past Jupiter, past Earth, in to the sun. It was already so far from home that it took more than five hours for each pixel, travelling at the speed of light, to reach Earth.

The sun was still striking, a brilliant point object millions of times brighter than the brightest star. But the planets, even the gas giants, were mere points of light.

Even so, had Voyager repeated the experiment now, it would have been able to observe the changes that swept over Earth, in the year 2015.

As the clouds rolled across the face of Earth’s oceans, the planet became a brilliant point source of reflected sunlight, its color lightening from blue to white, a twin of scorched Venus.

Patiently, conserving its attitude fuel, the blocky spacecraft sailed further from the sun, pointing its antenna home, obeying its iterated software instructions, calling steadily to Earth.

As Titan’s long night drew to a close, Benacerraf and Rosenberg prepared for their expedition to El Dorado, the crater on Cronos, in search of kerogen.

Working in the scuffed-up gumbo around the orbiter, they prepared to load their sleds. The sleds — six feet long, two wide — were improvised from Command Module hull sections, and had a covering of parachute canvas. Right now the sleds were configured to slide across gumbo; later, on Cronos, Rosenberg expected them to face a surface of raw ice, so they were carrying runners made from steel struts.

The equipment pile was dauntingly high.

Benacerraf bent and started to haul gear up onto her sled, the heaviest stuff at the bottom. The bulky items responded oddly in the low gravity; she had to haul to get them moving, but then inertia took over and she had to guide them, rather than lower them, into the right place on her sled. She checked each item off on the ring-bound checklist she had strapped to her wrist.

The first item was the S-band radio they would use to navigate, triangulating off Cassini. Next came a light, high-density power cell, cannibalized from the skimmer, and bottles of oxygen and hydrogen to feed it. Every time they stopped and made camp they would have to recharge the batteries in their EMUs; and the power cells would have to keep them warm during the “nights.” There were spare lith canisters for scrubbing carbon dioxide from their suits’ circulation: precious, irreplaceable. Benacerraf packed a tent, the flimsy hemispherical affair taken from the skimmer.

There were skis, improvised from pieces of Jitterbug’s frame. A length of rope. A small bag of tools. Spare parts for the gadgets that would have to keep them alive, Clancy clamps and silver bell wires. Their snow shovels. A medical kit, assembled by Rosenberg: cream for their hands and Benacerraf’s lips, powder and gel and antiseptic cream for skin afflictions and wounds, plasters for blisters, cuts and rubbed raw patches of skin, drugs and painkillers, Lomotil for diarrhea. They had pethidine and morphine — opium derivatives — and various forceps, scalpels, hypodermics and stitching needles.

The rations were based heavily on what was left of the dehydrated stock they’d brought from Earth. Benacerraf hated to exhaust these final supplies, making them almost totally dependent on the CELSS farm thereafter, but Rosenberg insisted. Their diet; he said, was crucial. He had calculated they would each need five thousand calories per day. He showed her how the diet he planned would be high in fats — nearly sixty percent — whereas their normal diet was more than half carbohydrates.

When the load was assembled, Benacerraf had trouble closing her canvas over the top of it. She had to repack a couple of times, trying to balance the mass of the load and to give it all an even shape.

At last she had it tied up with rope. The sled, bound together, was the size and shape of a coffin. Benacerraf hoped that wasn’t an omen. When she was done, she felt exhausted already: she was hot, her breath pumping, her limbs aching from fighting the suit’s stiffness.

Rosenberg estimated that each of their sleds, on Earth, would weigh more than five hundred pounds: the best part of half a ton. Here, gravity reduced that to seventy pounds.

Five stone, to be hauled across a hundred and twenty miles, in full EVA suits.

She pulled her harness around her torso.

The sled harness was improvised from Apollo seat restraints and Shuttle orbiter foot loops. There was a bandolier set of straps she lifted over her shoulders and chest, and a belt around her waist. There was a buckle at the front of her chest, relatively easy for suited fingers to reach and manipulate, and adjustable straps on the shoulders. The most difficult thing about designing the harnesses had been ensuring they would not foul any of her suit’s essential equipment, like the control panel on her chest, and the umbilicals carrying oxygen and water from her PLSS.

She leaned forward, and let the straps take her weight. She adjusted the shoulder straps until they felt comfortable through the layers of her suit.

She thought it was ominous that her sled didn’t move at all in response to her body weight.

Benacerraf looked back, one last time, at Tartarus Base.

Discovery looked like a DC-10 that had come down in the ice. But her white upper surfaces were uniformly coated with tholin, obscuring what was left of the colorful Stars-and-Stripes and NASA logos. The big windows on the flight deck, streaked by tholin, showed no lights; the interior of the orbiter was black. All the non-essential systems in the orbiter had been shut down, so they could save every last erg from the Topaz reactors while they were away. And that meant almost everything, save the heating and the nutrient, lighting and air supply for the CELSS farm. She played her helmet lamp over the orbiter’s flanks, which glistened with gumbo; it looked as if Titan was drawing Discovery gradually into its icy belly.

She stood beside Rosenberg.

“You remember to cancel the newspapers?”

“Yes,” he said gently.

“Let’s get out of here.”

She turned her face resolutely away from the orbiter. Her helmet lamp cast a ghostly ellipse of white light on an anonymous patch of gumbo. The greater darkness beyond, which they must penetrate, was concealed.

She leaned into her traces, with her full body weight. Her snow-shoes pawed at the gumbo. The harness rubbed at her shoulders and hips.

The sled, stuck to the gumbo, wouldn’t move.

She straightened up and looked back. There was a hummock in the gumbo, just in front of her sled, to its right. She was catching on that.

She turned again, and leaned into the harness with her left shoulder. She jerked at the harness, throwing her weight into it, trying to keep her footing in the tholin.

She felt something give. She almost stumbled over.

She looked again. The sled had moved forward, a couple of feet.

Rosenberg whooped. “Way to go, Paula.”

“Sure,” she said. She’d covered two feet, out of a hundred miles.

She leaned into the harness again, and jerked. The sled moved forward, coming free of the sticky gumbo with a slurping noise.

She pawed at the slush, trying to keep a steady rhythm. It got easier once she’d started, as long as she maintained the momentum of the sled. Whenever she stopped, she could feel the sled sink back into the welcoming mud. Still, her movement was jerky and uneven, stop-start.

Soon it felt as if the canvas band around her stomach was crushing her insides against her backbone.

It would be a comfort to think the sleds would get lighter as they proceeded, as the two of them ate up the food. But Rosenberg was insisting that they retrieve every piece of waste they produced — every drop of piss, every dump — and haul it back to feed the hungry CELSS farm. It made sense. But the thought of hauling bags of her own shit for a hundred miles across the surface of Titan did not chime with her romantic dreams of what exploring, an alien planet should be like.

A wind blew up. It came straight in her face, heavy and dense, and the gumbo rippled sluggishly before her. Her suit temperature dropped as a wind chill set in; she could feel the hot diamonds of her heaters trying to restore the balance.

Rosenberg called, “We have to expect a lot of this. That wind is a katabatic. A gravity-fed wind, blowing downhill, out of the heart of Cronos—”

“Shut up, Rosenberg.”

She bent her head and pushed at the gumbo, the harness digging at her shoulders and hips, Rosenberg’s katabatic wind shoving against her chest, driving onwards.

The light level rose slowly. A burnt orange glow seeped uniformly into the sky.

The gumbo glistened before her, like a plain of dried blood, unmarked and without frontier.

It wasn’t like a dawn on Earth.

As the light came up, there was no sense of opening out, of liberation from the confines of the night. The horizon was so close by, just a couple of miles, and obscured anyhow by the murky mist and haze. And the sky overhead, even on a cloudless day, was a lid, complete and orange and seamless. It was like being in a box: orange haze above, purple-black slush below, bound in by a horizon as close as a fence. And as she walked, bringing nothing but more miles of tholin slush into view — no roads, no trees, no gas stations — she became oppressed, trapped by the lifeless murk.

Benacerraf started to develop sharp twinges in her shoulder muscles, and shooting pains in her shoulder blades. And besides, her right foot was beginning to feel cold and raw. Forward motion was only possible with sharp tugs at her load; she could feel the pressure points in her shoulders, waist, knees and feet.

She stopped, trying to work the stiffness out of her shoulders, but confined in her movements by the heavy suit. The pressure of the harness bands on her chest and gut receded, briefly; she could feel bruises gathering, and burns about her hips where the harness was too tight.

She dropped her head, and ploughed forward again, yanking the sled away from the cloying gumbo.

They spoke rarely.

Mostly, she was alone with the rasp of her breathing, the high-frequency whir of the fans in her backpack and the hiss of oxygen across her face.

She tried to dull out her thoughts, not to think about what lay ahead of her and behind her, how every step was taking her further from Discovery. She concentrated, for instance, on the familiar noises of her suit; she tried to imagine she was in space again, in low orbit above the glowing, beautiful Earth, and that the suit was a bubble of warmth and comfort around her.

But the pain broke through that too easily, from her sore foot, her hands, her shoulders.

She tried not to think about the silence on the comms links.

The extinction of mankind.Rosenberg, figuring from what he knew of the parameters of the rock the Chinese had dropped, said there could be little possibility of human survival. It was the K-T boundary event over again, he said.

What proportion of “mankind” could she have met during her life? A few thousand? And how many did she care about?

Three people, she thought. Just three. And now she couldn’t even find out if they were dead or alive.

Way to go, Paula.

Later, she got angry.

She got mad at her balky sled, every time it stuck in some particularly viscous patch of gumbo and dragged her backwards, yanking at all her sore points. She got mad at the dull Titan weather, at the winds that chilled her but failed to freeze the gumbo to a useful surface.

She got mad at Rosenberg. That wasn’t hard.

She could sink inside herself and pick over some aspect of Rosenberg — the things he said, the body stink when he opened up his suit — and chew on it inside her head for hours, she found, building up the irritation to a near-hatred. Even those CELSS farm baby carrots, too bitter for her to eat, which he religiously devoured, insisting they were good for oxygen deficiency.

She could plod like this, steadily hating Rosenberg, and then, when she looked at her astronaut’s Rolex, she’d find — if she was lucky — that maybe an hour had passed, bringing her that much closer to the moment she could stop.

After a time, though, even the anger didn’t work. There was too little stimulation for her mind, in the dull landscape of gumbo and haze; she was turned inward, her thoughts stale and repetitive, churning and festering, with no external distraction to relieve her.

Sometimes she wanted to howl, to raise her face to the orange sky and just scream like a frustrated ape. But she knew she couldn’t. If she did, it would let out the beast at last, the Bill Angel craziness she suspected lay deep within her. She would lose her ability to manage this, once and for all.

So she plodded on, muttering. Stick it. Stick it. Stick it. Until the urge to howl dissipated, and the blackness receded a little.

After five hours, they had completed six miles. Benacerraf was exhausted, the little water spigots in her helmet running dry, the air circulating in her suit stale.

Rosenberg pulled alongside her. He ran a gloved finger over her bandolier. “Look at this,” he said, and he lifted up a harness joint with a fingertip. The stitching was torn, and Benacerraf’s harness was twisted. “This joint is double-stitched, but these couch harnesses were never designed for the kind of stresses we’re subjecting them to now. I guess you didn’t notice. You’ve been dragging the sled with the harness out of alignment. Your torso must have been twisted. No wonder your shoulders hurt.”

“Rosenberg, I’m done. Let’s get the tent up.”

“We haven’t completed the schedule, Paula. Another three or four miles and—”

“I know about the schedule. I don’t care about the damn schedule, Rosenberg. I’m telling you I need a break.”

“It’s just that right now we’re in as good a position as we’re going to be. We’re still full of food, and our core body temperatures are high, and we’ve had plenty of reasonably natural sleep back in the hab module. Later, it’s going to be harder to—”

“Help me raise the fucking tent, Rosenberg, or you’re going to get a sled runner up your ass.” She pulled the parachute fabric off her sled.

Still complaining, he helped her haul out the tent.

The skimmer tent was a ball eight feet across. The airtight skin was reinforced with parachute canvas, to give it additional strength. Rosenberg roughly inflated it with a feed from oxygen and nitrogen tanks. They anchored it to the gumbo with ropes and wide, flat, anchor-like spikes, driven deep into the slush. The tent sat on the slushy surface of Titan like a sad beachball, its muddy yellow surface drab and uninspiring, fat air and power lines snaking into it from the tanks in Rosenberg’s sled.

Now the two of them worked with the snow shovels to cover the tent over with a thick layer of slush. This ought to retain some of their heat. It was slow work; the slush at first just slithered off the canvas, and it took long, hard minutes of labor before the tent was covered over.

Rosenberg led the way into the tent, crawling through the crude airlock. Benacerraf followed. In her bulky suit, she kept colliding with Rosenberg’s limbs and helmet; she felt like some bug crawling around inside a cocoon.

Rosenberg hooked up a low-watt light and an electric heater. “Wait a few minutes until we warm up.”

The elements of the heater started to glow crimson red, a sharp color very unlike Titan’s dull orange. She sat close to the heater, watching the elements grow brighter, seeing their multiple reflections from the layered visors of her helmet. It was, she thought, heat brought to this ice moon from the remote center of the Solar System.

Rosenberg spent the time fiddling with the spare PLSS. This backpack — intended for Nicola Mott — had been rigged with a powerful vacuum pump and blower. They would use it to keep the tent air circulating through its lith hydroxide carbon dioxide scrubbers. If either of their packs failed during the march, this spare would serve as a backup.

At last, Rosenberg said the air and temperatures were okay.

Benacerraf cracked the seal of her helmet.

Chill air gushed into her helmet, at her neck and over her face. Her breath immediately misted before her face, and gathered as frost on the glass of her faceplate. She coughed, and took a deep breath. The air was so cold she could feel it burning at her lungs, and digging into the flesh of her face. The warmth of her suit seemed to gush out at her neck, and the cold seeped deeper into her.

“My God, Rosenberg.”

“Can you breathe? What can you smell?”

She sniffed, but her nose seemed blocked. “It’s so damn cold.”

“I know. I’m sorry. It isn’t going to get a lot better.”

She tried again, dragging the air through her nostrils. The cold of it seemed to scour at her nasal passages, the back of her throat.

The air stank.

“Bad eggs,” she said. “Farts.”

Rosenberg cracked his own helmet now; she could see steam billow out around his face, as if his suit was a mobile sauna. He grimaced. “Methane,” he said. “Other shit too. Welcome to Titan, Paula.”

“Let’s get this over with.”

Benacerraf took off her boots and gloves; her fingers immediately felt numb and the tips turned pasty-white, but despite the cold, it was a relief to get the boots off her sore feet.

She began digging around inside her suit, opening zips, trying to get at her urine bag. When she had it, she tipped it up into a larger plastic storage bag. She tried to keep the whole operation sealed up, but her cold hands were clumsy, and a few drops of the thick piss escaped and splashed on the gumbo-streaked fabric of her sleeves. She sealed up the bag and passed it to Rosenberg; he pushed it into a corner of the tent, far from the heater, where it would freeze quickly.

Mercifully, neither of them had taken a dump into their suit collectors during the walk. That was something to face another day.

She plugged her PLSS into the power feed, to charge up its batteries. She checked the status of her lith canisters and other consumables.

Rosenberg had brought a couple of bags of Mount Othrys water into the tent. These had refrozen, of course, during the haul; now he held them close to the heater and mashed them up with his boot.

There was enough water for seven or eight days, enough to be able to make it back to Discovery from the edge of the ice sheet without resupply. After that, they would be on the ice of Cronos, and ought to be able to collect local water.

When the ice was melted, they used the water to drink, and to resupply the spigots in their helmets, and to rehydrate a couple of packets of food.

Washing, they had decided, was a luxury for this trip.

The menu was soup, rice, biscuits and chocolate, with a handful of baby carrots. Benacerraf gulped down her food as rapidly as she could. The soup made a tiny warm place at the center of her body. The carrots still tasted bitter, but Rosenberg devoured his, and she passed him her portion.

Rosenberg measured the amount she drank. They had to watch out for dehydration. Cold air couldn’t hold much moisture, and with every breath she took, her nose and mouth were trying to humidify the air. She could lose a gallon of water a day that way, through her nose and breathing passages. It was a vicious circle; the more she dried out the less thirsty she would feel.

She gulped down the last of her ration. “I’m done,” she said, shivering. “I think I’ll seal up again.”

He checked the Rolex strapped to his wrist. “Not yet, Paula. Remember what we said. We have to leave the suits open a full hour before sealing up; we have to get the moisture out.”

Benacerraf thought of arguing against that, but he’d already relented on the schedule today.

Anyhow he was right. If the dampness from her body seeped into the suit’s layers, it would shortcut their insulating effect. She could even freeze in there.

“Let me look at your foot,” Rosenberg said now.

“It’s just a friction injury.”

“Then let’s stop it getting any worse,” Rosenberg said mildly. “Come on, Paula. Doctor’s orders.”

With great reluctance, Benacerraf removed the sock she was wearing on her right foot.

The side of her foot was rubbed raw, all the way back to the heel. Rosenberg rubbed cream into it, and stuck a plaster over the worst of her blisters. “If this keeps up we’ll have to think about cutting a chunk out of that boot, I guess it wasn’t designed for hiking.”

“No. Thanks, Rosenberg.”

When Benacerraf had sealed up her suit again, she lay down on her side, facing the soft plastic wall, away from Rosenberg. When she reached out to the wall and touched it with her gloved hand, she could feel how stiff it was, and a rime of frost — gathered from their breath and the moisture emitted by the hot Earth-born bodies inside their suits — scraped off on her fingertip.

She would be waking up to darkness again, she realized, to another day of tough hauling across the bleak, featureless gumbo.

It was impossible to settle her head inside her helmet. The damn thing wasn’t designed to be a pillow, after all. Tomorrow night, she’d put some kind of cushion inside here, something from the sled. Anything soft, even a scrap of parachute canvas.

She closed her eyes and tried to ignore the stiffness of her shoulders, the way her hip dug into the ground, the soreness of her feet, the sucking cold of the icy slush below her.

The suit heater labored to warm her; gradually the cold of the tent was dispelled, and the fresh oxygen-nitrogen blowing across her face dispelled the stink of methane.

The news from home,they’d taken to calling it.

It was impossible to grasp the scale of it, and so she didn’t even try. Maybe their isolation and abandonment had, in an offbeat way, actually helped. After so many years away from Earth she found it hard to remember that there were members of the human race beyond the handful who had left Earth orbit with her, in. After so long in confinement, the hab modules and landing craft and pressure suits making up a series of high-tech prisons, stretching back years, it was difficult to imagine walking, unimpeded, in the open air. Even if by some miracle she could be transported home now, she suspected she would be some kind of agoraphobic, a recluse, shunning company and light.

Even her family, Jackie and the boys, seemed to be receding from her. After all, the boys had lived half their brief lives without Benacerraf. If she had been taken home, she wouldn’t have recognized them, nor they her.

They’d been cut off up here, on this ice ball in the sky. They couldn’t have gotten home anyhow. The fact that home may not even exist any more really didn’t seem to make much difference. She still faced the same grinding numbness, the same lengthy list of chores to stay alive, every time she woke up, whether humanity lived or not.

It made no difference.

They didn’t talk about it, much. Rosenberg never referred to people he had lost, places he would never see again.

But that was Rosenberg. He was probably happier up here on Titan anyhow; human society had never done many favors for smart, goofy kids like Rosenberg, no matter how much it needed their inventions.

As for herself, maybe she was working through some kind of post-shock syndrome. Christ knows, she thought, I’m entitled to. Here she was stranded with an unfit wacko on a moon of Saturn, and it looked as if the world had come to an end, and she appeared to be developing crotch rot. How was she supposed to react? Now here’s my plan…

On the whole, she concluded, however, she was handling this pretty well. In a way, even the walking helped. Even the pain. Something to do, to occupy her mind during the long, slow-time Titan days.

Sleep times, however, were harder to handle.

On the fifth day, they reached the lip of the ice plateau Cronos.

Benacerraf stopped, and leaned against her harness.

The break in the landscape was surprisingly sharp. Maybe a half-mile ahead of her, the gumbo visibly thinned. Then a ridge of eroded grey-white water ice pushed its way up out of the tholin, like a beach rising from some sludgy polluted ocean. The slope was shallow at first, but Benacerraf could see how it continued on upwards, until it was lost in the thick band of horizon haze. The ice was worn with gullies and grooves, like old sandstone, and Benacerraf could make out stripes and stains of tholin down the grey buttresses.

As far as she could see the ridge continued, a band of dull grey like a wall across the world, merging at last with the horizon.

Rosenberg came up to her, breathing hard, leaning against his traces. “Magnificent, isn’t it?” Rosenberg’s voice was odd: light, fragile. And his stance seemed awkward; he seemed to be leaning too far into the traces. She tried to look into Rosenberg’s helmet. But his visor was obscured by an orange reflection from the hazy sky, frost, a smear of tholin. Rosenberg was the doctor; Benacerraf had been focusing on her own minor ailments, and trusting Rosenberg to look after himself.

Maybe he wasn’t.

She looked up dubiously at the slope they would have to climb. “Magnificent. Absolutely. Let’s go on.”

She led the way once more.

It got easier, despite the slope. It was like climbing Othrys. The gumbo got gradually thinner and less clinging — though less supportive of the sled — until at last her snowshoes were clattering on bone-hard ice, and the sled’s base was scraping with an ominous grind across the slope.

She stopped again, and waited for Rosenberg to catch up. Even in such a short distance he seemed to have fallen a long way behind, and it took him some minutes to make up the ground.

“Time for the great changeover, Rosenberg,” she said.

His breath was a noisy rasp, and he didn’t attempt to speak; he just let himself out of his harness and began to unpick the knots on his sled cover.

They had to fix their aluminum runners to the bases of the sleds. Benacerraf found it difficult to handle the big wing nuts with her gloved hands. The first time she twisted too hard, and the thread of the bolt sheared right off, coming away in a spiral twist.

Rosenberg dug out a spare for her. “Take it easy,” he said. “Steel is brittle at these temperatures, remember.”

Next she fitted her skis to her feet. These were just slats of hull metal, with opened-out overshoes fixed to them for boots.

After stowing the snowshoes and lashing up the sleds, they resumed again.

It took her a few hundred yards to get used to the skis, and the half-sliding action they required. There was a lot of work for her knees and ankles, against the stiffness of her suit. Soon her joints were aching, and muscles on the back of her calves were announcing their existence with pulses of stiffness and pain.

But when she settled into a new rhythm, she seemed to make faster and easier progress than before. To haul the sled she was able to lean steadily into her traces, rather than having to yank at the sled as she’d had to over the gumbo, and that smoothed out the pains in the pressure points on her shoulders, hips and waist.

This haul was never going to be easy, but it was, she conceded, a relief to be free of the clinging of the gumbo.

For a while she felt almost exhilarated.

She reached the mouth of a wide, shallow gully.

In the white light of her helmet lamp, the gully walls were blue-grey, and there was a scattering of loose ice on the floor.

The slope further up was undulating — it was gathering itself into a series of huge, frozen waves — and the gully, although it got steeper and more narrow towards the end, seemed to offer the easiest route forward.

She looked back. A way below, Rosenberg’s gumbo-streaked suit and the yellow-grey canvas on his sled were easily visible against the orange-grey ice.

She pushed up into the gully.

She could feel loose granules crunch beneath her weight. But it didn’t get any easier to pull the sled; the friction actually increased, and she felt the granules grind beneath her skis.

She bent down, stiffly, and scooped up a handful of the ice granules. They were hard and round, nothing like the snow of Earth. On the surface they were loose, but a little deeper they stuck together — presumably thanks to a surface layer of organics — to form pebble-sized chunks that she could crush in her hand. What the geologists called duricrust, she thought.

She took a look at the runners on her sled. There were fine grooves scratched into the runners’ base by the ice crystals. She knew that at normal human temperatures, sleds and skates worked by melting a fine layer of water at the top of the ice, and then sliding across, lubricated by the water, with almost no friction. Here, these small, hard crystals wouldn’t melt under the pressure of her runners; they were like grains of sand, and what she was doing was more like dragging a sled across a desert.

She felt an unreasonable, crushing disappointment. They just got no breaks with the conditions here.

As her climb up the gully wore on, the gradient increased in severity. Soon she was free of the clinging granules, but now, to her irritation, the ice grew too slick. She just couldn’t win. Sometimes her skis slipped backwards at every step, and the only way she could proceed was to tack back and forth at forty-five degrees to the slope, which added a lot of extra distance to the whole.

Even so, soon she had risen so far that when she looked back the ground was hidden in the haze. And still the slope continued above her, eroded and ancient, up into the orange mists above. She got her head down and climbed on. She forced any thoughts of the future — even the pleasure of getting her boots off, or the distance they still had to cross — out of her head.

At last, she reached the top of the steepening gully. The landscape opened out before her. She seemed to have reached a plateau.

The ice at her feet was jumbled and cracked. And when she looked ahead, she saw a sprawling mass of ice, locked in suspended animation. Waves of ice, which must have been a hundred feet tall, reared up, caught in the instant of crashing against each other. Huge open chasms showed dark against the grey-white mass. There was noise here, too: deep groans resounded from the belly of the ice, pulsing back and forth across the broken landscape. Each ice wave was carved, sometimes into elaborate shapes, with fluted channels and sharp crests. The giant shapes marched to the close horizon, so big they were visible as they receded over the curve of the world, like ships sailing over a frozen sea.

A layer of methane cloud, dark and threatening, lay like a lid over the shattered icescape, obscuring the haze and merging with the ice at the close horizon into a complex band of grey, black and orange.

After some minutes, Rosenberg came staggering up the gully after her. He leaned against his sled, breath rattling, and stared out at the ice sea, which was reflected in his visor.

“Pressure ice,” he said. “Paula, I think this whole continent is a giant magma extrusion, distorting one whole side of the moon. It’s like the Tharsis Bulge on Mars. Maybe such features are common on small worlds like this… And all this ice is flowing slowly outwards and downwards from the magma extrusion, a huge, continent-sized viscous relaxation.”

Benacerraf looked around with new understanding. The pressure ridges were ice waves, magnified by Titan’s low gravity, frozen in time. She shivered, feeling dwarfed in space and time. If she could accelerate her perception — if she could live for a million years — she would see the ice flowing thickly away from Rosenberg’s magma mound, like warm icing off a wedding cake.

After a couple more minutes they pushed on, Benacerraf leading again.

She tried to select a route which would take them threading between the worst of the pressure ridges.

The waves took a variety of forms. Some of them were sharply defined ridges, some of them rounded hummocks; some took still more exotic shapes — rounded boulders, even torpedo shapes, forms out of nightmares, mounted on eroded, fragile-looking pillars that looked unable to hold up all that mass, low gravity or not.

Ways through the ridges were winding and uneven. She tried at first to use her skis, but the paths were too narrow and twisting, and the skis just got in the way. She took them off and stowed them in her sled. The paths were covered besides by an uneven layer of loose granules, difficult to judge; sometimes the granules crunched beneath her boots, taking her weight before bottoming out, but sometimes she would find her heel thudding against ice as hard as rock, concealed by a quarter-inch of gritty granules. Her sores and blisters chafed. Her sled bumped and rattled over the surface, every step a jarring uncertainty, and her harness dragged over her shoulders and waist, burning her. She found herself growing nostalgic for the miles of compliant, sticky gumbo.

She was forced to scale some of the ridges.

They were exactly like frozen waves, a hundred feet tall or more. She tacked at a shallow angle to reach the top of each ridge. At the top she turned so that the sled went ahead of her as she slid down the slope of the far side. Then it was time to clamber painfully up to the top of the next ridge. She was like an insect, she thought, struggling over the meniscus of some giant pond.

She had no crampons or ski-sticks; she had to paw at the surface with her gloves and the sides of her skis to gain leverage. Soon her knees and elbows were bruised, and her fingers and toes ached. Sometimes her sled slid sideways and pulled her back down into a trough.

She paused at a crest. The ice was bare and blue-grey. Gritty granules lay in the hollows. The ice here was polished, and when she ran a gloved hand over it, it felt as smooth as glass, hard as concrete. The wave had been scoured out by gritty granules, and then polished to a sheen by fine aerosol dust.

When she looked back, she could see Rosenberg toiling through the valleys between the waves. The great ridges thrust upwards all around him, dwarfing him, and his helmet lamp splashed little puddles of yellow light against the shimmering walls around him. Sometimes he would pass a clearer patch of blue ice, and his light would penetrate the bulk of the waves; Benacerraf would see the beam glimmering within the bulk of a wave, scattering and sparkling from complex fissure patterns within the ice, an arc of Earth light illuminating these giant, dead, silent fairy castles.

Rosenberg stopped, several times, and took samples, scrapings of the eroded surfaces. He photographed the wave shapes. He even measured the angles of the frozen crests. His voice was weak, but Benacerraf could hear his enthusiasm as he found the opportunity to do a little science. “So beautiful… Benacerraf, each of these waves might be a million years old. And as the wind wears away at them, it’s exposing ice billions of years older than that — ice older than life on Earth… so beautiful…”

She found a new hazard.

She had to skirt huge crevasses; they looked to be hundreds of feet deep, with walls of a clean Earth-like blue where her helmet lamp shone on them. As the ice flowed out of the heart of Cronos, it was splitting along gigantic faults.

The crevasses parallel to the flow weren’t difficult to handle, as they pointed the path she wanted to take, towards the heart of the continent. But in some places, where the ice was compressed as it flowed, the crevasses ran transverse to the flow. She had to take wide detours to reach a narrowing of each crevasse, so that she could straddle them with heir skis.

In the most difficult country there was a mix of transverse and parallel crevasses, presumably because of some distortion of the flow. The crevasses intersected, cracking the ice into gigantic, parallel pillars, some of which had tumbled and shattered, so it was as if she was picking her way across the smashed sidewalk of some giant, ruined city.

She kept a weather eye on Rosenberg; his progress was slow, but he was plodding along in her wake, his head down.

After some hours of this, she found a place to camp. It was at the hollow between two giant pressure waves, a patch of regolith granules not much larger than the area of their two sleds. They had to anchor the tent to the sleds, because their metal pegs would not drive into the ice layer.

All around, as far as Benacerraf could see in the orange-brown light, there were pressure mounds and cracks. Their little encampment was like a small boat, she thought, lost in a giant sea.

Before they could crawl into the tent, a wind came up, blasting through the valley as if through a wind tunnel.

This was the seventh night, some fifty miles from Tartarus, and they were getting into a routine when they established camp.

Benacerraf hadn’t managed to take a dump that day as she walked — which was the preferred way, because then at the end of the day they just had to dig the crap out of their diapers, and some semblance of privacy was maintained. But now she could feel pressure building inside her. She suspected she was coming down with some kind of diarrhea. It was probably the antibiotics she was taking.

“Sorry, Rosenberg,” she said in advance.

He was piping water into today’s ration bags. He looked at her, his eyes glassy, and shrugged.

She opened her suit as wide as she could. She stood up and bent over in the tent’s cramped confines, with the open front of her suit close to the heater. She fumbled to get an old ration bag inside the suit. She found her butt. The skin of her buttocks felt flaccid, the flesh depleted of fat. It was, she thought, an old woman’s ass. She clamped the bag as best she could over her butt, and let go.

The crap emerged as a hard, hot spray, accompanied by an explosive fart. She tried to catch it all in the bag, but it wasn’t easy, and she could feel excrement splashing her hands, sleeves and legs.

The smell, erupting from the interior of her suit, was moist and pungent. My own contribution to Titan’s methane layer, she thought.

She closed up the bag and pulled it out, and her first priority was to close up her suit, trying to trap whatever warmth was left. Then she swathed the bag of sludgy excrement in a couple of other bags, wiped her hands on the back of her legs — the stuff would freeze off there tomorrow anyhow — and lodged the bag in the corner of the tent, with her piss bag.

She huddled closer to Rosenberg and the fire, shivering, her arms wrapped around herself.

Rosenberg was working at the cooking, but slowly. His left hand had got frostbitten a few days before, when damp had gotten inside his glove, and the cold of the ice ridges to which he had to cling had found a route to his fingers. Now, three of his main finger blisters had burst, the dead skin falling away to reveal raw stumps, like uncooked meat.

“Rosenberg, that looks like agony. You want me to take over?”

“No,” he said. His face was thin, the flesh disturbingly slack; his cheeks seemed to descend in folds over the corners of his mouth. “It’s not so bad now the blisters have burst. Before, sometimes the fluid in them would freeze.”

“Ouch.”

“We both got problems. Here. Eat.”

She took her food packets; the warmth, cupped in her hands, was welcome.

The meal passed in uncompanionable silence.

During the last couple of stops, the sour thoughts she’d previously been able to leave outside the tent’s airlock had started to seep inside.

She’d come to loathe Rosenberg’s personal habits. The yellow stink of his urine bags. The icicle-like dribbles of snot and saliva and tears that formed on his spindly beard. The way the wounds of his hands wept over her food.

And she started to become obsessed with the fairness, or otherwise, of the way Rosenberg handled the food.

The business with the carrots was one thing. Benacerraf had tried again to eat the things, but failed. So he got to eat all the damn carrots. And now Rosenberg had developed other little habits. Like he would take her discarded soup bags, turn them inside out, and lick the inner surface clean of any residue, before stowing them for use later. It drove her crazy. She started to insist on a turn making the soup, so she could get to lick the bags.

The NASA rations, in their bags and tins, were easy to split fairly. But the stuff from the CELSS farm — the carrots, their crude bread, wheat, rice — had to be divided. And if they had to choose between two portions, Benacerraf became obsessed by the need to stop Rosenberg getting the bigger portions, every damn day.

They came up with ways to deal with it. They took turns working the food. If something had to be split, one would make the break as fairly as possible, and the other got the chance to choose. They would alternate that, day by day.

Benacerraf got to look forward to the times when she could make the choice after Rosenberg’s split. That way she was guaranteed to finish up with a few fractions of an ounce more than he did. She woke up remembering it was her turn, with a lighter mood.

She understood what was happening here. They were both in such foul and increasing discomfort that they needed someone to blame. The real candidates were too impersonal and remote to be hated, satisfyingly: Titan’s ghastly conditions, the lousy equipment, the treachery of NASA and its political masters in abandoning them here, the Chinese and their hammer rock.

There was nobody else to blame. Only each other.

Understanding it, though, didn’t make it any easier to contain.

After the meal, they went to work on each other’s wounds.

Benacerraf had developed hemorrhoids, a consequence of the sweat and moisture trapped inside her suit. Rosenberg had brought a cream she could apply. Her back, shoulders and stomach were sore continually now, from their battering by the sled harness. It felt as if her pelvis was starting to protrude through the raw patches over her hips, as her body fat fell away. Her lips were still a problem; the scabs and crevices stubbornly refused to heal, and she still swallowed salty blood with every mouthful of food.

And she had indeed developed crotch rot; her inner thighs and the area around her pubic hair were rubbed raw by the inner layers of her suit, even though she treated the area with Canesten powder.

Rosenberg had a dose of crotch rot too. With the innocence of a child, he showed her his genitals. His scrotum was a shrunken bag, red raw from the rot. And somehow his penis had gotten nipped by the frost. It had swollen up to a shapeless mass, and the end was blistered. He shrugged. “What you pay for being circumcised. One less layer of insulation. Add that to the list, Paula. No Jews on Titan, without boxer shorts.”

He took a look at Benacerraf’s right foot. For days she had been favoring the foot as she marched, but that had just generated more problems. Now she had an abscess, swollen up on her Achilles tendon, where her heel was pressured by the rim of her boot. Rosenberg had been giving her antibiotics from their precious, dwindling supply, but they seemed to be doing little but give her the squirts.

Today, Rosenberg said he would have to operate.

He gave her two deep injections of Xylocaine. For a couple of minutes he covered up her foot, protecting it from the cold while the anaesthetic took hold. Then he took a scalpel blade — one he’d sterilized back in Discovery — and plunged it deep into the swelling. He made diagonally crossed incisions with brisk, confident strokes.

Yellow pus poured out of the wounds, and he collected it in an empty ration bag.

When he was done he cleaned the wound, coated it with antiseptic, and bound it up with bandage.

Benacerraf turned and began to pull on her sock.

When she sealed herself up again that night, Benacerraf found herself immersed in a deep animal stink. She knew that inside her high-tech suit she was becoming progressively more foul and filthy. She was an animal, stranded far from home and encased in this technological bubble, gradually fouling her own mobile nest.

The hell with it. For now, the dirt was another layer between her and the cold.

She turned her face to the tent wall. She pictured the way Rosenberg picked icicles of snot out of his nose-hairs. Warmed by irritation, she sought sleep.

At last the giant ice ridges began to diminish.

She came to a place where the waves, somehow sheltered from the wind, were smaller — no more than six or seven feet high, reduced almost to a human scale. Benacerraf decided to change her tactics, to attempt a frontal assault.

She waited to make sure Rosenberg was in view; then she donned her skis again and set out directly east, cutting across the first wave, a characteristic frozen wave-shape.

Hauling her sled behind her, she made it to the narrow ridge at the top of the wave. Her sled was suspended halfway up the slope, and the harness hauled back at her, rubbing the chafed parts of her skin. The ridge of the next wave was only about four feet away, and she reached out towards it, hoping to bridge across the gap with her feet. But the sled fouled on a ridge of the ice, and jammed; she was hauled backwards, and almost lost her balance.

Irritated, she leaned forward and lunged, trying to clear the sled. It bounced into the air and came free suddenly; unbalanced again she tumbled forward, scrambling with her skis to avoid falling down on the steep far side of the second wave.

So she proceeded.

The waves gradually declined in size, until she found herself skiing almost unimpeded over a plain of ridged ice, scattered with gumbo and pockets of gritty granules.

Gradually, they penetrated the heart of Cronos.

On the ninth day she started to find the going harder. After a while she realized the ground was sloping up beneath her. She pushed on through the uniform haze, ignoring the pain in her knees and feet.

The slope became dramatically steeper.

The ground was pushed up into a wall as far as she could see, from north to south, like one giant wave, its termini disappearing into the misty horizon. The ice was uneven, scoured by ankle-snappers: narrow, gumbo-streaked gulleys which plunged down the steepening contours.

She walked a zig-zag path, at an angle to the line of steepest slope, and that got easier on her feet, because the skis, sideways on, laid over all but the widest of the gulleys. But the gulleys snagged repeatedly at the runners of her sled, jerking her backwards.

Beyond the miniature horizon created by the crest of the wall, a mountain was rising, its grey-white flanks streaked by gumbo, like a model of Othrys.

The crest of the ridge came up suddenly. The ground levelled out and she found herself on a narrow, eroded shelf, maybe fifty yards across, puddled with gumbo. With a final effort she hauled her sled up and over the edge. She unbuckled her harness, and dropped it gratefully to the ice.

She looked back the way she had come. Her runners and skis had left no visible trail on the bone-hard ice. She could see how this great wall swept up out of the plain in a smooth concave sweep. Much further down the slope she could see Rosenberg; he was a dark, toiling speck, dwarfed by the bulk of the sled he hauled.

She turned and walked forward to the far edge of the wall. The ice here was smooth and relatively free of gulleys and crevasses, and she slid easily on her skis.

She reached the edge of the wall. She stepped carefully, avoiding the edge and any brittleness there.

The wall stretched to left and right, foreshortening and dimming out in the horizon mist. Its inward curve was just visible. That mountain peak, a neat cone, lay dead ahead of her, its base lost in the murky haze of distance.

She was clearly standing on the rim of a crater, a great walled plain which curved around that central peak. It looked too symmetrical to be natural, like a huge artifact.

She looked down into the crater plain. The wall here was steeper than on the other side; the crater was clearly a wound dug deep into the countryside. In a belt at the foot of the wall the ice surface was shattered into giant chunks which would make travelling difficult. But beyond that chaotic country, the land smoothed out, and was coated by a thickening layer of purple gumbo.

The sky was a dome of unbroken, twilight orange, empty of cloud save for a high, light scattering of nitrogen-ice cirrus.

Rosenberg came up to her. Like Benacerraf he’d discarded his harness; as he stood alongside her he leaned forward, letting the mass of his pack settle over his center of gravity, and his arms dangled, limp. His breathing was as noisy as ever.

“El Dorado,” he said. “I guess we made it. It looks just like in the radar images.”

She stared at the crater floor gumbo. She could see that it wasn’t the uniform purple-black bruise, color she’d become used to, back around Clear Lake. Purple predominated, but there were streaks of lighter reds — even a trace of scarlet — mixed in. The whole mess looked like a puddle of oil paints, the multiple colors mixed up and streaked together.

“Well, it’s different,” she said. “Do you think there’s kerogen?”

“I can’t tell,” he said testily.

“Try your IR.”

He reached up to switch on his night-vision visor. “I don’t know if this tells me anything or not.” Then he lifted his head, and in his visor she could see the reflection of the mountain, the orange sky.

“…Oh, wow,” he said. “Look up there, Paula. Use your infra-red. Oh, wow.”

She turned on her own visor, and looked up.

Through the milky-gold haze, beyond the feathering of cirrus cloud, was rising the huge, multicolored crescent of Saturn.

It was almost local noon here, so the sun was directly over her head. Saturn looked as if it was tipped on its side, a half-shadowed hemisphere with its bright round belly thrusting upwards. And jutting ahead of the globe of the planet, pointing vertically up towards the sun, she could see the brilliant rings, thin, striped ellipses.

It was the first time she had seen Saturn since they had dropped out of orbit;

Suddenly she realized where she was. It was a surge of perspective, as if the walls of the Universe opened out around her.

She had let this sunless bubble-world of ice and gumbo and haze and crotch rot eat into her imagination, until it was as if the gumbo extended on, beyond the visible, to infinity.

In fact, she was crawling over a ball of ice, a billion miles from the warmth of the sun.

I’m on Titan, she thought. Here I am — Paula Benacerraf, human, American, grandmother — gazing up at the rings of Saturn.

I made it.

They camped in the lee of the crater wall, on the edge of the chaotic terrain.

Rosenberg, a shapeless mass in the layers of his grimy suit, crawled over the tent floor and inspected Benacerraf’s feet. That early injury to her right foot still hadn’t healed up, and now she had frostbite in a couple of the toes of her left.

Rosenberg himself had developed some kind of tremor, rendering his own fingers too clumsy to apply the scalpel precisely. Benacerraf did most of the doctoring for both of them now.

Under Rosenberg’s direction, she lanced the swollen lump on her right foot, and the worst frostbitten toe on the left. Multi-hued liquid matter pulsed out of the new wounds.

The throbbing pain ebbed slightly.

“I don’t think that right foot of yours is good news, Paula,” Rosenberg said. “I think you have a deep-seated infection in the bone itself.”

“Terrific,” she said.

“I’ll increase your antibiotics. We still have some Metronidazole and Flucloxicillin. They’re not the most effective, but—”

“It’s all we have. I know.”

She used the scalpel to slice off squares of paraglider fabric, and plastered them all around the wounds. She pulled her socks back over her feet, wincing when the fabric tore at her new incisions.

She helped Rosenberg pull open the layers of his own suit. She had to pull carefully at the fabric, she found, or she would tear away great transparent strips of flesh, like sheets of onion-skin. The flesh seemed loosely attached, but nevertheless caused a lot of pain to Rosenberg when they came loose.

It was scary. She had problems herself, but loose skin wasn’t one of them.

Inside the suit she could feel Rosenberg’s ribs, the bony ledges of his pelvis, the slack thinness of his legs. The bulk of the suit masked this degeneration; out on the surface all she could see was his clumsiness, his slumps and lousy posture. It was astonishing he could walk at all, let alone haul a heavy load across the surface of Titan.

She rubbed cream into his armpits and stomach, the raw regions of his crotch. She even worked the cream into his frost-nipped penis, which was still swollen and sore.

Hemorrhoid cream was all they had left. But it seemed to soothe.

She hated to do this, to be so close to another human. She’d make a lousy nurse, she thought. To get through, she made herself think of how she’d handled Jackie as a kid.

He lectured her about their Belsen-like boniness.

“It shouldn’t be a surprise, Paula. We’ve been expending calories at a hell of a rate. More than we’ve been replacing them with food. We’re slowly starving, in fact. We’ve already metabolized a lot of our body fat, shifting it as a fuel supply into the bloodstream. All this is part of our bodies’ strategy to cope with what we’re putting them through: heavy exercise, without enough fuel. Our bodies are eating themselves up, trying to keep going as we demand…”

“Eat your soup, Rosenberg.”

With his hands swathed in lengths of parachute canvas, Rosenberg tried to raise his soup spoon to his lips. His hands shook too much, and the spoon clattered pitifully against his teeth, like a bird tapping on a window.

She put her arm round him to steady him, and guided his hand to his mouth. He sucked the soup gratefully.

Later they lay, back to back, in the confines of the tent. There was nothing before Benacerraf’s eyes, through the window of her helmet, save a patch of plastic wall reflecting the dim low-energy bulb, and a couple of piss bags, slowly freezing.

“You know, Paula—”

“What?”

“Sometimes I want to give up. Just stop. Lie down on the ice, or in the granules or the gumbo or whatever damn stuff, and just stop. Go to sleep. You know?”

“We can’t call in a rescue chopper.”

“I know, Paula. It makes no damn difference.”

She lay silently for a moment. “Then why do you go on?”

“Why do you?”

She thought that over.

“Because of Jackie.”

“Your daughter.”

“Yes. And her kids. In case they’re watching me, the stills and video we transmit.”

“Paula, we haven’t heard from Houston since—”

“I know. I didn’t say it was logical.”

“So it’s the clan. Right? You got the clan in your heart, even here, a billion miles away, on Titan. So far away you can never do anything to affect them again, for good or ill, or they you. Even though the world has ended.”

“Yes,” she said. “If you want to be anthropological about it. I’m doing it for them. Can’t you understand that, Rosenberg?”

“Sure. It’s just primate logic.”

“So what about you? What stops you giving up?”

He slouched; it was a shrug, masked by the layers of his suit.

She turned over, to face his huddled back. She reached over his waist and put a gloved hand over his; his glove felt as if it. was empty. “Listen, after eleven years I know you. You back off into generalities and theory whenever anyone gets too close. Tell me why you keep going, Rosenberg.”

At length, reluctantly, he said: “Curiosity. I always wanted to know how it all worked, Paula. It drove me crazy to think that one day I would die, and I’d never see all the science and exploration and discovery that would follow me, all the things people would figure out. And now, here I am on Titan, for God’s sake. A world nobody’s visited before. Every hill we climb offers the prospect of something new, something nobody’s seen. Right now I’m excited.” He smiled at her weakly. “I mean it. I’m looking forward to getting this kerogen, or whatever it is, back to the hab module. Maybe it will keep us alive a little longer. And even if not, it’s something nobody’s seen before.”

“At least you made it this far.”

“Yeah. But—”

“But what?”

“If the Universe is just a puzzle box, it doesn’t mean a damn thing, does it? It’s not enough. Not any more; maybe it never was.”

Rosenberg had reached a kind of ultimate logic, she thought. He must be spending his walking time addressing the final question science couldn’t answer, in this godless age:

Why bother to live at all?

But that wasn’t really his problem, of course. She’d never met anybody who knew themselves worse than Rosenberg. Except maybe Bill Angel.

Rosenberg’s problem was that he was alone. He’d come all the way to Titan, because of that, and now he was here, and he was still alone.

“Rosenberg,” she said.

“What?”

“If it’s any consolation, I need you. I’ve never depended on anyone so much in my life. No human has been more dependent on another, than you and I.”

“More primate logic, Paula?”

“We are primates, asshole.”

“This is just perlerorneq, Paula.”

“Huh?”

“The winter blues. An Inuit word. Goodnight, Paula.”

“Goodnight.”

They walked into the crater basin, and loaded the sleds with as much crater-bottom tholin as they could carry.

They turned, for home.

The journey didn’t get any easier. Her sled was even heavier than when they had set off from Tartarus, laden with bags of frozen urine and feces, and with canvas-wrapped bundles of kerogen-soaked gumbo — so they hoped — from El Dorado. And as Rosenberg had weakened, she had been forced, surreptitiously, to transfer some of his load to hers.

Once again Titan’s slow rotation had taken this hemisphere into night. They would stay in darkness, in fact, until they reached Discovery. So she walked on, with only a splash of light from her helmet lamp ahead of her, and the faintest of diffuse orange glows from the haze above and around her.

The pain in her feet dominated her mind. It was as if she was trapped in some tunnel, walled in by pain, receding ahead and behind her to infinity.

She tried to objectify the pain itself.

She imagined the pain as outside her, even as a living thing, a malevolent creature. It was a red-hot poker embedded in her bone, a crucifixion nail driven into her foot, a gigantic invisible snake-head with its jaws clamped over her foot…

If only there was some way she could make it stop. If she was on some dumb stunt of a polar expedition, she’d call in the relief planes right now. If she was subject to some ghastly torture, she’d confess, give in, betray anybody or anything. Just to make this stop.

But through all this the pain was still there, lurking beneath the distracting superstructures she erected inside her head. And every time she slipped or caught her boot on a ridge in the ice the pain would come bubbling up, overwhelming her conscious thought, raw and primeval.

She kept getting ahead of Rosenberg. Each time she stopped, it seemed an increasing wait before his circle of helmet lamp light came weaving across the ice towards her.

The journey just went on, without meaning save survival, day after day.

After fifteen days out, they got back to Tartarus Base.

In the light of her helmet lamp, the orbiter and Command Module, side by side, were just mounds in the gumbo, their surfaces streaked by bruised-purple tholin deposits. They were unrecognizable as man-made artifacts save for their symmetry of construction.

Somehow, Benacerraf was disappointed. She’d been building this place up in her mind as her home, like a cliche of a family-Christmas fireside, somewhere warm and safe that would shelter her. But it was no such thing, of course; all there was here was a couple of downed spacecraft, a tiny, shivering farm, a cooling nuclear pile.

She unbuckled her traces. She retraced her tracks, back towards Rosenberg. Her footsteps, in the dim yellow light of her helmet lamp, were shallow, infilling craters in the gumbo.

She got them both into the airlock. She cracked their suit seals and took off their helmets, boots and gloves. Rosenberg’s helmet came away with strips of skin and tufts of hair and beard clinging to the lining.

She led him through into the interior of the hab module. The air here was hot, thick and moist, hard to breathe, and so sterile it almost smelled antiseptic. Bizarrely, she found herself missing the warm, almost cozy suit-stink she’d been immersed in for two weeks.

She helped Rosenberg to one of the Command Module couches. He sat there like a melting, gumbo-streaked snowman, his bony hands dumped in his lap, his head slumped forward.

Benacerraf made her way to the far end of the hab module, her ruined socks leaving trails of sticky blood on the clean metal surfaces.

She stripped off her own suit. She was stiff all over, particularly in her lower back, shoulders and hips; it was painful to put herself through the contortions required to shuck off the suit’s layers. The inner layers clung to her damaged flesh; she had to tease the cloth and plastic away from her skin, trying not actually to break her epidermis or pull away scabs. The suit was worn and badly damaged in places. They’d been lucky the suits had worked to carry them so far — the EVA had been well beyond the suits’ design limits.

At last the suit lay as a heap of soiled Beta-cloth at her feet.

She stood naked, shivering despite the cloying warmth of the hab module.

She was skeletal, her ribs protruding under flat sacks she didn’t recognize as her breasts, her buttocks lumpy and flaccid, her knees and elbows hard knobs of bone. Her feet were a mass of lumpy, pus-filled growths and open frostbite wounds and scars. Crotch rot spread from the dark triangle of pubic hair, out over her thighs and belly, angry red. There were pressure sores where the harness had dug into her, and where her suit had chafed, over her hips, under her armpits and around her chest and waist. Her personal hygiene during the EVA hadn’t been too effective. Her upper legs and buttocks were flecked with yellow urine stains and smears of what looked like dried excrement, and there were patches of glaring red skin infections around her waist and legs, the parts of her body where she hadn’t been able, or willing, to reach.

She allowed herself two minutes to shower. The hot, clean water felt like acid on her skin; it was actually painful to have the layers of filth lifted from her ghost-pale flesh.

She padded to her quarters. She pulled on underwear, and an old Beta-cloth T-shirt and shorts. She tried to don her Beta-cloth slippers, but they wouldn’t fit over her swollen sores; so she wrapped old T-shirts loosely over her feet and bound them up with duct tape.

She gave herself a moment to run her hands over her belongings, her books and photos, anchoring herself once more in these relics of her life, her personality.

As an afterthought, she put on a facemask and a pair of surgical gloves. Then she made her way to Rosenberg.

He was still in his suit. She stood him upright. He felt disturbingly light. His head was a mess, the hair matted with filth and patchily bald; there were cracks around his mouth, nose and eyes that had opened into fissures as deep as razor slices, dribbling thin blood.

Slowly, she got him stripped. His undergarments were even more matted with waste and filth and blood than hers had been. It looked as if he had suffered some kind of dysentery attack and fouled his pants; when she pulled off the suit, hot stinking liquid flowed out over the clean floor of the hab module.

Benacerraf got his longjohns away from his arms and lowered them around his legs. A shower of skin fragments and pubic hair fell onto the metal at Rosenberg’s feet. His legs and groin seemed to have been stripped clean of skin, left raw and compressed into folds. His kneecaps were just ripples of flesh, his genitals rubbed raw. She could see deep wounds dug by the edges of the harness straps, and within the patterns of straps she found eruptions like small, festering boils.

The soles of Rosenberg’s feet had split, each of them, down the middle: almost neatly, like the soles of cheap shoes. The casts of dead skin came away like plastic moulds in her hands, leaving roughened, raw tissue, from which a watery fluid leaked.

“Dear God, Rosenberg.”

He whispered, “It’s not as bad as it looks.”

“What the hell is wrong with you?”

His head lolled, and he sighed, his voice a rattle.

“You know, don’t you?”

His head rolled around until he was facing her. “Yes, I know what it is. I think, anyhow. You need to take a few blood samples to—”

“Tell me.”

“Vitamin A poisoning. Those damn baby carrots.” He opened his mouth to laugh, and spittle looped between his lips. “Remember, Paula? They were too bitter for you. Well, you were right. More vitamin A than dog liver. Another failure of this toy ecosystem we’re trying to maintain here. No buffering… the whole thing’s too small… levels of toxin all over the place. We just couldn’t control it well enough. We gave it a good try, but it was going to get us in the end…”

There was a flap of skin, loose, beneath his ear. Like a ring-tab, she thought. With a sense of dread, she touched it. It was dry. She pulled at it.

The epidermal covering of Rosenberg’s ear came away intact, a complete cast. It drooped between her finger and thumb. “Oh, Jesus Christ.” She shivered violently and flung the thing away.

He fell against her, clutching at her arm. “You have to get the samples in, Paula. Look for the kerogen. Do it while I can help you. Everything depends on that — everything—”

His head lolled again, and he went limp.

Gently, she tucked her arms under his body, and lifted him like a child.

There had been no signal from the ground, of any kind. Benacerraf checked every day, and bounced test signals off Cassini, to ensure there was no fault with the satellite. And she sent transmissions home, regular updates, with their results, and some personal messages.

In case anyone was listening.

The choice was not to send at all, and that would have felt like giving up. Or as if, by her own loss of faith, by not acting as if there was someone left down there, she might actually somehow bring down the catastrophe they both feared.

She could picture Seattle, almost as vividly as if she was there. She could picture the house where she’d grown up, the places she’d lived with Jackie as a child, her grandchildren… It was more real, to her, than this murky shit-hole.

How could it be gone, ruined? How could there be nobody, walking the dog, watching the news, mowing the lawn?

In the privacy of her room, though, she grieved, little by little, for her family. It was as if she was allowing herself to face the huge loss, piece by piece.

What she feared most was the thought that she and Rosenberg might be all that was left. She hated the idea that her actions, the rest of her trivial life, had suddenly become so significant.

She wished she had some way to climb up above the clouds, to lash up some kind of telescope and peer at the Earth, and see.

Rosenberg sat on a Command Module couch. He was wrapped up, pupa-like, in layers of clothing and thick blankets of Beta-cloth, but he still complained about feeling cold. He wore heavy sunglasses — they’d belonged to Bill Angel — to protect his eyes from the glare of the hab module floods. He’d lost most of his hair, and much of the skin from his scalp and face; swathes of raw tissue showed where his flesh was exposed, riddled by crimson crevasses.

Benacerraf made herself a meal: rice, boiled in Titan melt, with lettuce and some beef jerky from the stores. She sat opposite Rosenberg as she ate. She’d already fed him tonight, spooning the contents of one of their last soup sachets into his mouth, trying not to react to the blood and hunks of loose skin that followed the spoon back out of his lips.

Rosenberg had become the defining feature in her mental landscape now, as so much of her time was given over to caring for him: medical attention, tending to his basic needs — wiping my ass,as Rosenberg put it — and covering his work for him.

He told her what he’d found in the samples from El Dorado. His voice was a thin, robotic rasp.

“I found a lot of interesting products. Beyond the usual organic sediments that come from the stratospheric chemistry, there are traces of urea, organic acids, diacids, some amino acids. Products of tholin hydrolysis. Other amino acids resulting from cyanogen addition to nitriles. Results of cyanogen and nitrile polymerization, including imidazole, purines, pyrimidines. I got aldehydes, ketones, acetaldehyde — the results of alkyne hydrolysis. Some Strecker synthesis — aldehyde-nitrile condensation. Aldehyde polymers, including sugars, glycerol, some other species of—”

“Christ, Rosenberg. Did we find kerogen or not?”

“…No,” he said. “I’m sorry, Paula. I guess I was wrong; El Dorado can’t hare been a carbonaceous chondrite crater after all. My best guess now is that it was formed by a fragment, a calving of a much bigger bolide, which was probably water ice… There is a large water ice crater system a little further to the west.” His head rolled back and forth. “And that’s recent. Maybe the impact was in historic times. Maybe it could have been visible from Earth through a telescope, if anyone had been looking that way, a giant ice comet smashing into Titan… A hell of a thing.”

“So we’re fucked. The EVA was a wild goose chase.”

“All the products I found were the result of reacting Titan materials with water from the bolide. I’m sorry, Paula.”

She grunted, “It was a good shot. Anyhow, I didn’t have any smarter ideas.”

He seemed to be trying to lean forward; he struggled, feebly, within his Beta-cloth layers. “Look, Paula. We have to face facts. We’re beyond rescue from Earth. We’re on our own here. We ought to look at the worst case.”

“The worst case?” She laughed, around a mouthful of rice. “Look at us, Rosenberg. What could be worse than this?”

“We are the last humans.”

He fell silent, his breathing a noisy rasp.

She felt the motion of her jaw slow, without conscious volition. Saliva pooled in her mouth, flooding the rice grains and lettuce there, swamping her sense of taste.

Rosenberg said, “The great unspoken truth, huh.”

Deliberately she started to chew again; she swallowed a mouthful of saliva.

“But what difference does it make?” she said. “We’re fucked anyhow.”

“True. Without the kerogen supplement, our ecosystem isn’t going to last long. A couple more system crashes and we won’t be able to recover. We just aren’t viable here. We tried hard to make it so, but in the long term we were always going to lose. And the whole thing will die with the two of us anyhow.”

“Right,” she said brutally. “So what does it matter? Rosenberg, Earth is a billion miles away. We could try to eke out our lives up here for years, or we could blow up the damn Topaz today. So what? It makes no difference, except to ourselves.”

“You’re wrong, Paula,” he whispered, his ruined mouth gaping open. “I’ll tell you what difference it makes. We’re still part of Earth’s biosphere, even if we are a little seed pod transplanted across a billion miles. Even here, we’re still connected; in fact, we have a greater responsibility. We might be all that’s left. You and I as individuals are going to die here. But what we do before then might determine the future of Earth-like life in the Solar System. We have a responsibility, Paula.”

She stared at him. “You’re crazy, Rosenberg,” she said bluntly. “You’re such a pompous asshole. Everybody’s dead, except us, and we have no resources at all, and here you are talking about the destiny of life.”

His cracked lips spread in a grin. “I have a plan.”

“You and your plans, Rosenberg.”

“I think I know a place where we can find liquid water…”

The surfaces of all Saturn’s moons had been shaped by impacts. Titan’s surface had been shielded by its thick blanket of atmosphere, but its huge mass had acted to focus impacting objects onto itself.

Thus, there were impact craters all over Titan.

“Paula, think about a pool of impact melt at the bottom of a crater, dug into Titan ice, heated by the kinetic energy of the impact. It cools down to the freezing point, and stays there at constant temperature — zero degrees — as it freezes and shrinks. It can only lose heat by thermal conductivity. It’s a slow process. The conduction equations are well understood. And water is good at retaining heat…”

“It will stay liquid.”

“A crater a hundred miles across might have an impact melt pool ten miles wide. And it would take ten thousand years to freeze.”

She frowned. “So if the crater beyond El Dorado, the primary that spawned the smaller crater we found, is only a few hundred years old—”

“It should contain a pool of liquid water. With a concentration of organics of a few parts in a thousand…”

“Holy shit, Rosenberg.”

“Yeah. That’s not all. What about impact ejecta?” Ejecta was material thrown out after an impact, through the explosive decompression of the shocked solid surface. “On the Moon, ejecta is thrown out into a near-vacuum, and it’s a mixture of vapor and solid. But on Titan, with its thick atmosphere, you’ll have something more like the cratering process on Venus. Ejecta will flow in blankets over the surface, to three or four times the crater width, and maybe a hundred yards deep. And there will be a lot of organic-containing sediments mixed in with the surface ejecta flow. You can calculate the cooling lifetime using heat conduction partial differential equations which—”

“Cut to the chase, Rosenberg.”

“Yeah. There will be ponds of liquid water, maybe a hundred yards deep, scattered over the surface around the primary crater. Even they should last for centuries, maybe longer. They’ll freeze over, of course; so will the impact melt pool at the heart. It will have a thin crust of ice, but will be liquid beneath. With time, as the layer of liquid water shrinks, it will become more concentrated in organics, and you’ll get a whole spectrum of reactions: amino acids, aldehydes and ketones, nucleotide bases… In those pools, we should find an emulation of nearly all the prebiotic chemical pathways on the early Earth, except for the steps involving phosphates… Damn, damn.”

“What?”

“If only we’d gone a little further. I might have found it all, just waiting under the surface, a thin crust of ice. Just waiting for a seed.”

“Waiting for a… Oh.” Suddenly, she saw his plan. “You’re kidding.”

“No.” His sunglasses slipped down over his bony nose. His eyes were blue rocks in the crusty red mass of his face. “Paula, I’ll show you what to do. I made notes in my softscreen. You have to go back to Cronos again. Go further than we did before. Find the primary crater beyond El Dorado, and the impact melt pool at its center. Or maybe you’ll find ejecta ponds. Liquid water, Paula. I’ll prepare a package—”

“What kind of package?”

“Earth-origin microbes that can metabolize tholin.”

“We don’t have the facilities for genetic engineering.”

“We don’t need to engineer them,” he snapped. “Don’t tell me my job, Paula.”

“I’m sorry.”

“I’m talking about common soil bacteria. Aerobic and anaerobic… Clostridiunt, Pseudomonas, Bacillus, Micrococcus… They are present in our nutrient solutions in the farm. They can extract their carbon and nitrogen requirements from tholin…” He started coughing, big spasms that racked his body inside its Beta-cloth shroud. “Drop them in that liquid-water soup of prebiotic organics and they’ll thrive… Earth life, surviving on Titan…” He coughed again.

She stood before him. “Rosenberg, maybe you ought to rest. I’ll clean you up.”

“No.” His eyes were still steady, despite the shuddering of his body. “I have to be sure you understand. The responsibility.”

“I know.” She knelt before him and put her hand on his bony arm. “Responsibility for the future of Earth’s biosphere. All on your shoulders. I understand, Rosenberg,” she said gently. “But—”

“But what?”

“I still don’t get it. Even if I find the ponds, even if I seed them, they’re just going to freeze over, in a few hundred or a thousand years.”

“Sure.”

“So what’s the point?”

He shuddered. “Things will change. In time — billions of years, Paula — the sun will reach the end of its life. It will become a red giant… And then, for a time, Titan will be as warm as the Earth. Titan summer. Maybe our bacterial spores will give rise to a new evolutionary sequence. You see?”

She pulled back from him. Suddenly she felt chilled. “You think big, Rosenberg.”

“Little packets of bacteria… Seed the planets, the comets. If you’re serious about spreading life to other worlds, that’s how you’d do it. Cheap, too. It’s absurd to carry humans around… all that plumbing…” His eyes closed, the big broken lids sweeping down like curtains.

She picked him up, and carried him to the hygiene station.

Sitting on the floor of the hab module, a Beta-cloth blanket thrown over them both, she cradled him. His head felt huge in her lap, the massive skull with its paper-thin covering of flesh and skin, but his body was feather-light.

He whispered: “How can I die? How can the world keep turning without me? I’m unique, Paula. The center of the universe. The one true sentient individual in an ocean of shapes and noises and faces. How can I die? It’s a cruel joke.”

Dear Rosenberg. Analytical to the end.

“They’ll remember you for coming to Titan. A member of the first expedition. That’s one hell of a memorial.”

“If there is anyone left to remember. Anyhow, even so, I’ll just be a freak in a circus show.”

She said gently, “No god waiting for you, Rosenberg?”

He tried to laugh. He whispered, “What do you think? God died in 1609, when Galileo raised his telescope to the Moon, and saw seas and mountains. We flew to Titan. But with that one act Galileo discovered the universe. God can’t share the same cosmos as a Moon like that.”

“No,” Benacerraf said sadly. “No, I don’t suppose He can. But where does that leave us, Rosenberg?”

“Fucked,” he said brutally. “Science is a system of knowledge, Paula. Not a comfort.”

“I know,” she said. She stroked his forehead, and crooned her words, as if to a sick child. “I know.”

He gripped her arm with a claw-like hand. “Paula. You have to put me through the SCWO.”

“Sure, Rosenberg.”

“I mean it. You can’t afford to waste the biomass. But freeze yourself, Paula. Go out on the ice, when… It’s important.”

He coughed, but even that had lost its vigor. The color seemed to be draining from his face, even from the exposed tissue there, as if his blood was drawing back to the core of his body.

His head rolled on its spindle of neck across her lap. “You know, I’m not afraid. I thought I would be. I’m not.”

She squeezed his hand; it felt as if his bones were grinding together. “You don’t need to be afraid, Rosenberg. I’m here.”

He said, with a spark of sour energy, “It isn’t that. The human stuff, monkeys holding hands against the dark. I never thought that would make any difference. And I was right. But you and I—”

He coughed, and shuddered; his ruined eyes fluttered closed.

She leaned over, closer to his bleeding mouth.

“You and I, with what we’re doing here, are the most important humans who ever lived. We will cast a shadow across five billion years. And that’s a hell of a thing,” he whispered. “A hell of a thing.”

He relaxed, with a rattling sigh, and lay still, collapsing into her arms with a slow-motion, low-gravity calmness. “You know, I learned a lot,” he whispered. “More than I expected.”

“You did good, Rosenberg.”

“But you know, I never figured out why…”

“What?”

“Why did it feel like this?”

She could feel his body settle, the internal organs relaxing and losing their tension; the last gases escaped from his stomach in a long, low fart.

She got him into the frigid ground only an hour later.

The grave was just a shallow ditch, scraped out of the gumbo, already infilling. His naked body lay at its base, thin, skeletal, glistening with the frozen water ice of his body.

Once again she had to find words to say over a corpse.

She checked her transmission link to Cassini. She wanted this moment to be sent to Earth. Maybe there was somebody there to listen; maybe not. If there was, maybe this would somehow help them.

“I’m sorry I didn’t have a flag to wrap you in, Rosenberg,” she said. “Anyhow, I know this was what you wanted, in spite of what you said. And if you think I was going to have your sorry ass circulating around my ecosystem, you got another think coming.

“Casting a shadow across five aeons.Maybe you will at that. You did good, Rosenberg.”

I guess that will do, she thought.

She threw a handful of Othrys ice crystals into the grave, and began to drag her snowshovel over the gumbo, filling in the shallow pit.

In the last days she spent a lot of time in the CELSS farm, trying to stabilize it as much as she could. She kept power supplied to the farm, and left it seeded with a new crop, of wheat, barley and lettuce.

She felt a great responsibility for the drawn, etiolated little plants here. They were, after all, the only living things other than herself on this whole moon, and she felt loyal to them, and regretted she was abandoning them to die.

But there wasn’t much she could do for them. She figured the CELSS farm might last without human intervention a few weeks, before a pump broke down, or a nutrient pipe clogged, or a short burned out half the lamps, or some runaway feedback biocycle caused the miniature ecology to crash.

Even if by some miracle that didn’t happen, eventually the power from the Topaz reactors in Discovery’s cargo bay would fail. The lights would dim, and the last, spindly plants would finally die, as Titan’s cold broke in.

She took spare seeds and wrapped them in airtight bags. She buried them, under a marker, in the gumbo outside Bifrost. That way, perhaps they would survive, deep-frozen, until Discovery’s next visitors came this way, whatever became of her.

She spent a last night in the hab module. She took a long, hot, luxurious shower, extravagantly spending, the reactors’ reserves of energy.

She tried to read a book on her softscreen, but could barely concentrate. She kept on thinking that this would likely be the last book she ever read. The words seemed just a foolish dancing, against dark emptiness.

She put the softscreen aside.

She looked at her images of Jackie and her grandchildren. She stared into the sunny photos, trying to will herself into the pictures with her family.

She slept well, in her quarters, with the lights off and the door closed, shut in against the shells of emptiness around her: the deserted hab module, the empty moon, the billion miles separating her from Earth.

When she woke she ate a gigantic breakfast, using up a lot of stores: dried apricots, an irradiated breakfast roll, rehydrated granola with blueberries, ground beef with pickle sauce, noodles and chicken, stewed tomato, pears, almonds, drinks of grapefruit and strawberry.

She went to the hygiene station and took a long, slow, luxurious dump. She cleaned herself with antiseptic wet-wipes.

She stripped naked. She folded up her Beta-cloth clothes neatly and put them away in a drawer. She washed one last time, then put plasters and bandages over the places where she knew to expect problems from cold and pressure sores: her toes and ankles and the sides of her feet, her hips, stomach, chest and shoulders. She put cream — all that was left was the hemorrhoid ointment — over her groin, in anticipation of crotch rot.

She pulled on her suit. She took great care over each layer; she wouldn’t get another chance to fix it, and she would hate to go to her destiny with a fold in her underwear rucked up her ass.

Inside the suit layers, duct-taped to the fabric, she stored Rosenberg’s canister of bacteria samples — protected there against the cold — and a little packet of photographs, old-fashioned hard-copy images, of Jackie and the kids.

She sealed up her helmet, gloves and boots, and ran methodically through the suit checklist fixed in its ring binder to her arm. She went through the list twice. In a way her biggest dread, now she was alone, was that without anyone to check her she would miss out some crucial step, kill herself through carelessness.

She looked around the hab module one last time before leaving it. It was clean, tidy, everything stowed away, as if ready for reoccupation. She felt obscurely proud; she’d remained civilized to the end.

Just like Captain Scott.

She slipped on her Apollo hull-metal snowshoes and stepped out into the gumbo. The tholin slush sucked at her feet with its familiar stickiness, and she felt Titan cold immediately seeping through the layers of her suit.

She looked over Tartarus Base.

She could make out the delta shape of the grounded orbiter, with the cone of the Command Module alongside. The cover they had erected over the open cargo bay of the orbiter was still in place, the parachute fabric stiff and streaked with gumbo. In a final extravagant gesture she’d left the flood lights of Discovery’s flight deck burning; the yellow Earth-like light now glared out through tholin-streaked windows, shining over glimmering slush.

There was little geologic activity here; the ground was stable. Even the tholin deposition rate was slow. It might take a billion years, Benacerraf thought. But at last Titan would claim Tartarus, its patient tholin drizzle ultimately covering over the pyramidal peak of Apollo, Discovery’s big boattail. The spacecraft hulls would ultimately crumple and shatter, until nothing remained of this, the first human outpost on another planet, save a thin, isolated layer of metallic crystals, and a few anomalous deposits of organic residue.

She looked up, towards the marginally lighter horizon. She cut in her IR visor and made out the spark of light, pixel-blurred, that was the sun. From here, the entire orbit of Earth was a circle the size of a small plate held at arm’s length, with the planet itself — with all its freight of humanity, and hope and love and war and history — a dull-glowing bead on the rim of that circle, impossible to make out. She could hold up her bulky gloved hand and obscure the entirety of the orbit, the whole span of human experience before the Discovery expedition.

She buckled the Command Module couch harnesses around her. She dug her snowshoes into the gumbo and shoved. Immediately she felt twinges from the sites of the pressure sores she’d suffered last time, at her hips and chest and shoulders.

The sled came free of the clinging gumbo with a sucking noise. She staggered forward.

The sled was heavier, this time, than when she’d set out for her previous extended EVA with Rosenberg. This time, all the essentials — the tent, the recharged skimmer power cells, all her food and water — were stacked high on this one sled.

On the other hand, her food load was lessened. Just enough for a one way trip.

Soon, she managed to settle into a steady rhythm, with each step jerking the sled free of the gumbo which clutched at it.

Every instinct told her that Rosenberg’s billion-year scheme couldn’t work.

It was, of course, a typically arrogant technocratic fantasy — in a way an extension of the gigantic, ludicrous journey they had undertaken to come here — to suppose that it would be possible, with a handful of micro-organisms thrown into a lake of ejecta melt, to reach out across billions of years and shape the evolution of a world.

For instance, Rosenberg had made a lot of assumptions about the viability of bacterial spores over such huge deserts of time. And who could really say what the future evolution of the sun would be hike? Nobody had actually watched a star follow through its ten-billion-year evolutionary cycle, from birth to death; every theory was inferred from humankind’s mayfly-like snapshot perception of the stars that happened to be scattered through the universe today. Maybe the red giant sun would grow so huge it overwhelmed Titan, boiling away its atmosphere in moments. Or maybe the sun would just go nova, blasting Saturn and its ancient moons to fragments…

It was, she thought, a pretty dumb plan.

But, in the end, it gave her a goal.

Thus her life would end, she thought: struggling to fulfil another project, one more technological dream, because she had nothing better to do.

After a few paces she looked back. Tartarus Base was already lost in the thickening orange haze, the deepening gloom of Titan twilight.

After forty-eight hours, the last light had leaked out of the orange haze layers.

Benacerraf walked through the dark, fighting the resistance of the invisible gumbo as it sucked at her sled and snowshoes. All she could see was the splash of lamp-light on the glistening gumbo hide ahead of her, its diffuse reflection from her own nose and eye ridges, the ancient bone structure of her own human face.

Titan was a world of, enclosure.

She lost track of time, of the day-night cycle of the distant Earth. She would check her Rolex in the light of her lamp, and find that ten, or twelve, or fourteen hours had worn away, as she had driven on through her tunnel of blindness, dark save for the splash of light from her helmet lamp, silent save for the scratch of her breathing, the whir of fans and pumps in her backpack, the muttering of her own voice.

…She brooded. What if Rosenberg had been right, in his worst-case projections?

What if the clouds had rolled over the face of Earth — what if she was, truly, the last spark of awareness in the Solar System?

There were theories that consciousness was a quantum process. That reality — the Universe itself — was called into existence by conscious minds, as, by observation, they collapsed the infinite possibilities of each quantum wave function into a single, definite event, embedded in history.

The Universe, it was said, needed consciousness to create itself.

Then what if she was the last?

Here she was in this bubble of darkness, the limits of her personal cosmos reaching no more than five or six feet in any direction. Was there anything beyond the intangible walls of the hazy dark? Did she call into existence new stretches of the gumbo as she walked over them?

If she did not look at the Earth, did Earth any longer exist?

And when she died, as the last bit of consciousness departed, would the world — Titan and ringed Saturn and the remote sun and Earth and the stars — would all of it fold away and dissolve, with the cold grey light underlying creation breaking through, like, a projector’s lamp through a trapped and burning film frame?

At times she felt more frightened than she’d ever been in her life.

She welcomed the familiar pain of the harness pressure points and in her feet. The pain gave her something to think about, outside her own sterile thoughts.

She made camp, proceeding slowly and carefully, double-checking every step before she trusted herself to crack the seal of her suit.

She cleaned herself out. She felt free to dump her bags of frozen urine and feces rather than haul them with her. She tended clumsily to her various wounds and injuries.

She developed another big, ugly abscess, this time on her right foot around the ankle, where a flaw in her boot had rubbed and caused her skin to blister. She decided she had to lance it. She took a sterilized scalpel, closed her eyes and stabbed at the abscess, letting the momentum of her bunched fist ram the blade into her flesh. The pain was extraordinary, sharp and penetrating, much worse than when Rosenberg had operated on the same kind of injury.

When she looked down, pale, watery pus was leaking from the wound. She squeezed out as much matter as she could, and wiped the incision with a scrap of parachute fabric. Then she dosed it with antiseptic fluid and dressed it.

She ate from a packet of reheated soup, and drank melted Othrys water. Then she sealed up her suit and lay down against the plastic tent wall, layers of parachute fabric beneath her.

She propped her photographs in front of her helmet. She stared into those fragments of bright Seattle daylight, trying to believe she wasn’t alone, as she waited for sleep to claim her.

She made rapid progress.

She reached Cronos, and crossed its rim of pressure ridges. She skirted the walls of the crater they’d called El Dorado.

She walked into Titan’s murky daylight once more.

Beyond El Dorado, high on the gumbo-stained ice plateau of Cronos, she came to a ridge of broken, jumbled ice, maybe twenty feet tall. She had trouble hauling her sled over this; several times she had to go back and grab the lip of the sled, dragging it bodily up and over.

When she reached the crest of the ridge, she was facing a plain that looked as if it had been crudely assembled from jammed-together blocks of ice. Pressure ridges criss-crossed it.

The persistent, bone-deep cold seemed to recede. It was warmer here.

She descended the ridge, and began to make her way over the plain. The blocks and upthrust ribs in the ice were a foot or more high, and frequently snagged the runners of her sled. The ice creaked and shuddered; evidently great plates of it were sliding over each other in vast tectonic evolutions. She had the sense of riding the scaly hide of some huge, sluggish animal. But that elusive warmth seemed to gather.

She stopped. With the edge of her ski she scraped away the thin layer of gumbo and loose ice crystals from the surface.

The ice seemed thin: perhaps a foot thick, or even less. She thought she could see a dark liquid beneath the complex flaws of the ice, and bubbles of some gas trapped there.

At last she came to a dark break in the ice surface. It was a lead, a stretch of open water, within a crack in the ice maybe six inches deep. The water was dark and scummy, polluted with tholin and hydrocarbons.

“Hot damn,” she said. “You were right, Rosenberg. I wish you could have gotten to see this.”

She loosed her traces and leaned clumsily over the lip of the crack. She dipped one gloved hand in the water. Immediately the cold penetrated the layers of her glove, and the heater diamonds stung her flesh. Close to its freezing point, the water was a hundred and seventy degrees above the ambient temperature.

Water was molten rock here. It was as if some suited monster had come to Earth, and dipped its hand into the scalding red-hot lava stream of a volcano. But she was the alien, here on Titan.

She lifted out her hand. Away from the water surface the air temperature dropped quickly, and the droplets of oily water that clung to the fabric of her glove spread and froze, turning to frost patterns. When she closed her fist the frost crackled and broke away, hard ice fragments falling back to the water’s dark surface.

She stepped over the crack in the ice and hauled the sled across.

She came to more leads of open water, slick with hydrocarbons, opening and refreezing. Some of them were too wide to risk crossing, and she had to detour, tracing up. and down between the leads. In some places the ice was so thin it was spongy and creaking, and if she stepped too close to an edge it would crumble away into the open water. She found a lead that was closing, its edges grinding noisily together. Where the two plates met, the ice was cracking, its sharp sounds ricocheting out across the emptiness, echoing from the iron-hard ice.

The ice field stretched on; ridges and plates pushed out of the plain like pieces of gigantic, abandoned furniture. From all around her rang out the aching, grinding noise of moving ice, crackling like the shock waves from a Shuttle launch. The noises came together in great waves, punctuated by godlike silences.

As she penetrated the field of frozen-over ejecta, the visibility opened out, the pervading gloom of Titan’s orange sky lifting a little. Thin methane clouds, dark and tangled, blew ahead of her, obscuring the tall orange sky. Perhaps the relative warmth of the water was clearing the air of some of the organic haze.

At last she came to a place where the broken layer of methane clouds, ahead of her, grew still darker. The darkness — near to black — seemed to begin in a sharp discontinuity, almost a straight line, scraped across the sky.

She smiled. Rosenberg had warned her to expect this.

It was a water sky.

There must be a wide stretch of open water, no more than a few miles away, reflecting darkly from the low methane clouds of Titan.

She pitched her camp on a large plate of ice, hundreds of yards from any open leads. The air was so warm that she was able to strip off the outer layers of her suit. It felt like a great luxury, as she rubbed handfuls of half-melted ice over her bruised skin to clean herself.

She drank her fill of cool comet water.

That night, as she lay huddled against the tent’s plastic wall, she listened to the muffled groaning of the thin ice beneath her. She imagined the slow swell of the comet water, the big underground waves travelling back and forth across the ejecta sheet.

At any moment this plate could crack, pitching her into the cold water, suit and all. But somehow that wasn’t a frightening prospect. She was, after all, made of water. Water was home.

She slept, without dreaming, as well as she had done since Rosenberg’s death.

She went through her waking ritual for the last time.

She breakfasted on dried strawberries, crackers, and tiny, sweet lettuce leaves from the CELSS farm. She took a final dump, into an empty plastic food bag, and cleaned herself thoroughly.

She blew her nose on a fragment of parachute fabric. It was the last time she’d be able to do that, even.

There was a last time for everything, she thought: not just the grand actions, but the small, human things. It all counted.

She pulled on her suit. She tucked her little packet of photos inside her suit, over her heart. She sealed her helmet and gloves, and turned the switch that powered up her PLSS. She heard the familiar high-pitched whine of the pumps and fans, the cool hiss of the oxygen blowing over her face.

She packed away what she could: her food and waste bags, the power cell. Soon, the tent was as neat as she’d left Discovery.

She pushed her way out of the tent’s cramped little airlock. Outside, standing on the thin, grinding ice, she tucked Rosenberg’s canister of spores under her arm, to keep it as warm as possible.

She looked around her little outpost. The half-empty sled stood on the ice, its parachute-fabric cover loosely knotted over it. The tent, closed up, was compact and neat.

She fixed her Hasselblad to the S-band antenna stand, and lined it up so it framed the tent and sled. She checked that the antenna was still aligned correctly on Cassini; it was possible the drifting of the pack ice during her sleep had pushed it off its line.

Feeling self-conscious, she went to stand in the camera’s field of view. Standing there before her little camp, in her grimy, battered, much-repaired EVA suit, she held up her canister of spores, while the camera fired image after image up to Cassini.

She hated these Armstrong poses. But maybe, she thought, this one was justified. After all, if Rosenberg was right, with this one act she might be shaping the future of a new biosphere.

These might be the most important photographs ever taken.

She wondered whether to smile or not.

Her residual sense of orderliness made her walk around the camp once more, checking everything was intact and stowed away.

Then she turned and strode off, across the ice, towards the water.

A wind began to pick up, blowing off the broken ground in front of her, hard and piercing; she found she relished its resistance.

She could feel her packet of photographs, a hard rectangle pressed against her chest by the suit.

She felt as if she was discarding her life, in huge layers: first Earth itself, shrunken to a pinprick of light by the huge distance she’d travelled; then Tartarus Base, with its painfully assembled and repaired life-sustaining gadgets; and at last even the trappings of her own little encampment out here on the water ice. Now, she was left with nothing but her body, and the battered suit that was its last protection.

The leads began to widen and interconnect.

Soon the ice was broken up into isolated islands, some only a few feet across, separated by channels of grey, scummy water. Ahead, fragmented ice stretched in a loose mosaic. She could see the open water ahead of her, a dark band encroaching from the horizon, flecked with loose ice floes.

She pressed on, climbing over the narrower channels, taking care to stick to the larger ice floes. But the ice was fragmenting rapidly. Soon, even the biggest floes were unstable beneath her feet.

She couldn’t go any further. This would have to do.

She kicked off her skis, and stacked them neatly to one side. She wouldn’t be needing them any more. She took a last sip of orange juice, from the worn plastic nipple inside her helmet.

She walked to the edge of the ice. She took Rosenberg’s canister of spores, and dipped both her gloved hands in the water. The cold of the water was a thrilling shock, easily penetrating the feeble resistance of the gloves’ heating elements.

Under the water, she opened Rosenberg’s canister, and shook out the spores, scattering them as widely as she could.

When the canister packet was empty she withdrew it, shook it clear of ice, and tucked it neatly into a sample pocket, buttoning closed the flap.

Then she stood straight. She looked around at the haze-drenched world around her: the cramped, close horizon, the scattered darkness of the methane clouds above, the shattered ice landscape, with that band of free water, just out of reach.

She reached up and snapped the switch on her chest that shut down her PLSS.

The sound of pumps and fans died immediately. The air stopped washing over her face, and felt thicker, more stale. The cold of Titan dug into her flesh through the pattern of heating elements. And she could hear the moan of the wind, a remote bass tone, and the deep crackling of the ice sea, emerging from all over the landscape.

It was the first time she’d heard the music of Titan, unmasked by the man-made noises of her equipment.

She walked forward, across this icy beach.

Before she could reach the edge of the floe, the ice crumbled under her weight.

There was a moment of falling — extended by Titan’s low gravity — long enough for a small stab of terror to dig into her consciousness. But then her feet and legs hit the thick, oily surface of the water. The meniscus rushed up her body, its cold mass enclosing, and joined over her head.

Her suit made her more dense than the water, and so she sank into darkness.

She fell slowly. She let her arms and legs relax, and she felt them drift away from her torso, separated by the flow of water.

She turned slowly onto her back.

Above her she could see the surface of the water, the dim orange glow of the sky above, huge oily ripples creasing the meniscus. But the surface receded, its detail lost, and soon the sky was invisible, save for the faintest of orange glows.

The water felt comfortable as she fell deeper into it, as if she was returning to a kind of home.

Now, at last, it was all gone. The Universe had collapsed down to the layer of water that pressed against the surface of her suit, the bubble of air in her helmet. There were no more choices, no decisions, no plans.

Maybe this was mankind’s last moment, she thought, here on this remote beach, the furthest projection of human exploration. Maybe, in fact, the sole purpose of the human story, fifty thousand years of crying and living and loving and dying and building, had been to deliver her here, now, to this alien beach, the furthest extension of mankind, with her little canister of seeds.

The cold dug deeper. For a while she found herself shivering, and she wrapped her arms around her torso. But that seemed to pass, and she felt comfortable again.

She knew what was happening. This was hypothermia, her core body temperature falling, as her body heat leaked out through the suit’s unresisting layers into the giant welcoming mass of fluid beyond.

It didn’t really matter.

She thought she was unconscious for a time.

It was hard to be sure.

Then she thought she could see Columbia, far below, rising towards her.

She smiled.

The orbiter’s leading edges glowed, a faint orange. The floodlights in the payload bay glowed like a captive constellation. And beyond Columbia there were stars: thousands of them, easily visible to her dark-adapted eyes, like the blackest desert night on Earth. She could even see the great sweep of the Galaxy, the ragged edge of the dust-clouds at the core.

The EVA was over. She reached up her hands, and started to take off her helmet.