Titan n-2

by Stephen Baxter

When an ammono walked, its limbs would straighten out. Then icicle legs would ripple around the rim, flashing pink highlights, their motion too complex to follow. The table-top body of the ammono would glide evenly over the surface, through seven or eight yards, until it found another place to sample.

  Actually, the ammonos hardly ever moved.

  Only one in a hundred would be in motion at any time, save for the delicate clatter of limbs; this scattered herd of them together was almost stationary, eerily so, their Zen-like stillness quite unlike the chaotic jostling of terrestrial creatures.

  She remarked on this to Rosenberg.

  He grunted. “Paula, chemical reactions are dependent on temperature. By the time you get to the region where ammonia is a liquid — under thirty degrees below zero — you’re looking at a relative rate of maybe a hundred to a thousand times as slow as at room temperature for us—”

  “You’re saying these creatures have a slower metabolic rate.”

  “Much slower, yeah. You can see it in the way they move: those long periods of gathering energy, then a quick burst of motion. But it’s not going to be as simple as that, of course… reactions with the right activation energies won’t chill out, so they would be selected preferentially. And all that ammonia will have a complex effect, helping or hindering reactions. The only way to know for sure would be to take one of those critters apart, and see what’s sloshing about inside its carapace.”

  That suggestion offended her.

  She bent to pick a flower. “Maybe we shouldn’t be asking questions.”

  “Huh?”

  “Here we are at the end of time. Everybody we knew — everything we understood — is long gone. What does science, figuring things out, matter now? These ammonos seem to have given us a place we can live. Maybe we ought to be content with that.”

  He laughed. “If my forebrain had an off-switch, I’d agree with you.”

  She dropped the flower and walked on.

  When she looked back, after a few paces, an ammono had crawled laboriously over to the flower and was picking it apart with its scalpel-sharp claw.

  They took breakfast on the hoof. Benacerraf tore off handfuls of mushroom flesh and washed it down with water from an ice-flecked brook they found. She splashed water mixed with snow over her face and scalp; the cold was sharp and refreshing. One good thing about being hairless, she thought: at least it was going to be easier to keep clean.

  As she walked on, her breath steaming ahead of her, she started to warm up. Soon she had to pull open the seams at her shoulders to keep cool. But the suit must be porous; it wasn’t trapping excessive amounts of heat and sweat.

  “Somebody remade Titan, Rosenberg. Engineered it so we could live here. Breathe the air, eat the fruit. Who? People?”

  “No. I think it was the ammonos, after the sun got too hot for them, and they had to retreat. Titan ice is primordial stuff, Paula. It probably contains dissolved carbon dioxide, ammonia, methane, organic molecules, sulphur, salts. When it melted it must have out-gassed volatiles. Good for building a new atmosphere.”

  “Volatiles I can understand. But this is an ice moon. Where did the topsoil come from?”

  “Any particulate matter in the ice would settle out, as dirt on the sea beds. Maybe the ammonos dredged that up. Hell, I don’t know.”

  “They, Rosenberg? Why did they do all this? Why are we here, for Christ’s sake?”

  He had no answer.

  As they neared the base of the horizon-spanning cliffs, the ground began to slope upwards and grew harder and colder underfoot. The topsoil was sparser than on the lowland plain, the vegetation struggling to get a foothold, although there were still clumps of tough dune-like grass struggling out of cracks in the ice bedrock.

  Soon it became more of an effort for Benacerraf to continue her steady Moonwalk bound over the surface.

  There were fewer ammonos here; in their shining transparent suits they trooped, in their reptilian spurts, back and forth, evidently shuttling between the plain and some kind of base on the Cronos plateau.

  A wind blew up, pushing parallel to the cliff face and across their path. Clouds shouldered across the sky: fat cumulus clouds of water vapor, just like Earth’s. And then a rain began to fall, big fat heavy drops that descended with a snowlike slowness, and splashed noisily against her golden-brown suit.

  The horizon disappeared, and an orange-grey mist closed in around her, obscuring the cliffs.

  Rosenberg came up to Benacerraf. He had slipped his hands inside his sleeves, and wrapped his arms around his body; rivulets of water ran down from the dome of his head. “If this cliff is the edge of Cronos,” he said, “we’re heading due east, roughly.”

  “Or maybe west,” she said. “We don’t know which side of the continent we’re on.”

  He shook his head, and water sprayed off around him. “No. This has to be the western periphery.”

  “How do you know?”

  He pointed upwards, then tucked his hand back under his armpit. “We can’t see Saturn. I figure we’ve been returned to the region of Tartarus Base. Anyhow, the winds are blowing out of the north. Which is what I expected.”

  “How come?”

  “Titan is still a small world, Paula. The weather system is going to be simple. Like on Earth, the sun’s heat at the equator pushes up piles of moist clouds. The clouds flow north and south, dumping their rain on the way. But here, the gravity is so low and the distance to the poles so short that I’d expect the hot air to make it all the way to the poles. When it descends, that’s where you’ll find the deserts…”

  Mercifully, he stopped talking.

  Benacerraf looked up. The huge sun was visible as a brighter disc above the grey-white clouds. Raindrops, fat and slow, fell towards and around her, like a hail of bullets falling from infinity. Some of them had turned to snow, now, and they swirled languidly in the updraughts.

  She was shivering; the rain on her bare scalp was cold and actually painful. The few ammonos here had their arms tucked under their carapaces, and rain puddled on the clear coatings over their backs. And now the rain actually seemed to be getting harder, turning to sleet.

  “Shit, Rosenberg. Understanding the mechanics of the weather wouldn’t help me half so much as a hat.”

  He nodded, his motions jerky, shivering. “Let’s keep moving. At least that will keep us warm. This can’t last forever. Maybe we’ll climb above it.” He set off.

  She tucked her head into her shoulders, folded her arms across her body, and walked after Rosenberg, who was already receding into the misty haze.

  The walking didn’t require much attention, and, like her walks on Titan before, she tried to lose herself in daydreams, fantasies, to escape the dull reality of the world.

  But the dreams wouldn’t come.

  Maybe the ammonos had rebuilt her, but they didn’t seem to have put back her imagination. Or maybe there was some part of her which knew there was nothing much for her to dream about.

  By the time they reached the foot of the cliffs, the rain had stopped, but there was still a thick layer of laden cloud which obscured the upper reaches of the cliffs. The cliffs here were steep and forbidding, thrusting out of the ground like a wall, their base littered with some kind of loose scree.

  Rosenberg went forward and tried to clamber over the scree, but it was slick with half-frozen rain, and the fine plates slid over each other easily. Despite the buoyancy of low gravity, Rosenberg slipped, repeatedly, and stumbled.

  After he bloodied his nose he gave up.

  The chaotic clusters of ammonos had reduced to a couple of files here, like columns of ants. They were going head-on at the cliffs, without hesitation; their legs seemed able to clamp onto the slick ice surface, and they hauled themselves straight up even the steepest sections of the cliff. Looking up, she could see the trail of ammonos dwindling into the mist and low cloud above, their carapaces dark stains against the dull grey-red surface of the ice cliffs.

&nbs
p; “I wish I had their legs,” Rosenberg said, rubbing his mouth. “Come on. We’ll follow the cliffs a ways. It can’t all be as tough as this.”

  They stood, shivering, each waiting for the other to lead. Neither of them wanted to do this, she realized. The truth was, they both just wanted to go home.

  She said, “Which way? North, or south?”

  “You choose, Paula. What difference does it make?”

  “North, then.” She turned to her left and began to walk. “And if we walk all the way to the pole and find a desert there, I’ll know for sure you’re a smart ass, Rosenberg.”

  “That’s my job,” he said, wiping blood from his lip.

  After a couple of hours of steady walking over the slick ground, they came to a narrow gully. As far as Benacerraf could see it was incised all the way up the ice face, and into the clouds above. It looked as if it had been cut by a stream, which was now vanished.

  At the foot of the gully there was a short section of the treacherous scree. She stepped carefully over this, watching her feet.

  Then she came to the gully itself. Its mouth, at the base of the cliff, was broad, and there was a litter of topsoil, evidently washed down from the gully sides or from the Cronos plateau above.

  She walked forward. For a hundred yards the going was easy; the ground sloped up steadily, but the gully was broad and paved with gritty, rough topsoil. But soon the walls narrowed around her, and the base of it narrowed to a thin V. She had to walk — climb, in fact — with her feet splayed outward, braced against the gully’s two sides.

  As she climbed, the grip of her soles became less reliable, and her feet slipped from under her. The clutch of gravity was feeble, but the pain was great as she banged her knees and hips against bone-hard ice. Her bare hands soon started to turn white and numb from the cold of their contact with the ice. She pulled her sleeves down over her hands and gripped the cuffs in her clenched fists. But that wasn’t satisfactory, because the stretched material rubbed painfully at her shoulders and the back of her neck. And besides, it was almost impossible to get any grip without opening out her fists.

  Her world closed down to the aches of her body, the few feet of ice gully around her, the eroded surface in front of her face, the focused search for the next handhold. She couldn’t even move fast enough to work up a decent sweat, and she grew steadily colder. She was a billion miles from home, aeons in the future, but as her discomfort closed in she might have been anywhere, she thought. Her irritation turned to misery.

  She climbed into a layer of billowing mist. The droplets of water vapor were hovering balls the size of her thumbnail, and they caught the diffused crimson light of the sun. They looked too big to be suspended in the air, but here they were, the swirling updraughts easily counterbalancing Titan’s feeble gravity. Walking through them was something like entering a zero-G shower. When the droplets hit her translucent suit they splashed but didn’t stick, and secondary droplets spun away, shimmering. But the drops that hit her face and hands and bald scalp spread out rapidly and soaked into her. Water started to seep inside the suit, at her neck and cuffs.

  She tried to wipe the excess liquid off her face with the edge of her hands, or her cuff. The mist as it dried was leaving a fine residue on her flesh, a sticky organic scum.

  She ached all over. The hell with this. She started to get angry.

  If she couldn’t lose herself in daydreams of past or future, then maybe she ought to concentrate on the present, the obstacles she was facing, how she could make things easier.

  Crampons, for instance.

  Maybe she could improvise something from those scrubby trees on the plain. A flexible branch, maybe a rope woven from some kind of creeper.

  She needed gloves, of course. And a hat. Maybe they could sew together some kind of fabric of leaves.

  She thought about knocking over one of those ammonos. That might solve all their raw materials problems. But if Rosenberg was right, the ammonos, inside their chill spacesuits, were breathing out ammonia and cyanogen. Slicing open one of those suits would not only kill the ammono, it would do the two of them a lot of damage too.

  Anyhow, such violence felt wrong. This wasn’t her world, after all.

  So: hats of leaves, or bark. Maybe they could stuff their suits with grass and lichen to improve insulation. They would have to do some kind of inventory of the vegetation here: investigate what they could eat, what they could use for other purposes, like construction and even medicine…

  Thinking, planning, wiping the waxy organic sheen from her face, Benacerraf continued her climb.

  At last the gully grew narrower. Looking up, Benacerraf could see she faced maybe ten or fifteen feet of sheer ice, beyond which the land flattened out. She could see tufts of grass-analogue bristling out from the lip of the plateau above her, black and wiry.

  It wouldn’t be a difficult climb, she thought. Just a little scary.

  She looked down. She’d risen almost all the way out of the mist layer now, she realized. The mist was a lumpy grey-white ocean beneath her, from which thrust this ice cliff. She could make out Rosenberg, as a toiling pink-brown speck in the mist layer, perhaps a hundred feet below her.

  She turned again, lodged her fingertips in crevices in the ice, and hauled herself upwards. The low gravity worked in her favor, and the climbing here was actually easier than the slog up the gully.

  She reached the top in a few minutes, and dragged herself up over the edge.

  The land flattened out here to form a plateau, sharp-edged by this ice cliff. Further off, she could see no sign of further uplands, although a shallow wave-like ridge in the ice hid much of the landscape from her. There was grass growing close to the cliff lip, and some of the swollen mushroom-like things. A layer of thin cirrus cloud coated the eastern sky, stained red by the light of the aged sun.

  She peeled open a couple of seams to cool down. She sat at the edge of the cliff, her legs dangling over.

  Rosenberg took a further half-hour to reach her. He hauled himself clumsily up over the last lip of rock and threw himself flat against the ice, his arms outspread. His face was coated with a thin frost rime.

  “I never thought,” he said, “I’d be so pleased just to be somewhere flat.”

  She scraped the frost off his skin with her fingernails. “You’re not a physical kind of guy, are you, Rosenberg?”

  “Oh, I’m learning to be. Boy, am I learning.”

  She collected some food, mostly mushroom flesh. They drank ice-cold water from a small rivulet nearby, that fed the bigger system that had carved out the gully they’d climbed.

  When his breathing had gotten back to normal, Rosenberg pushed himself to his feet. His hands and mouth full of mushroom flesh, he did a slow scan of the world from this new vantage point. He gazed down over the grey, lumpy clouds that covered the lowlands, then turned and looked inland.

  He stopped. Even his jaw ceased its chomping.

  “Rosenberg? Are you okay?”

  He was staring inland, a green light reflecting from his face. “Stand up,” he said. “Stand up and look at this. My God.”

  She got to her feet, her legs still aching, and stood alongside him.

  The sky to the east, over the interior of this ice continent, had cleared; the cloud layer was breaking up. The sun was a huge blood-red ball, battered and pocked, dominating the orange sky above.

  There was a layer of green light at the horizon.

  At first she thought it was a smog belt. But it was flat and sharply distinguished, at its upper edge.

  It was a roof.

  There were tall trees — no, towers — evenly spaced within the green. And the towers were tall, she realized now; they were poking above the horizon, their bases hidden by the curve of the moon.

  Some huge form, diamond-shaped, moved between the towers, within the roofed enclosure.

  “My God,” said Rosenberg. “I was starting to think I dreamt it. That’s where I was, the first time.”<
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  The first time? “Where?”

  “In there. That’s a worldhouse. The last refuge of the old ammonia-based life system. It’s like a greenhouse. Except, colder within than without. In there, the conditions must be as they were when the ammono life was at its peak, when it covered Titan. That’s where they retreated when the sun got too hot, when the ammonia oceans started to boil and the bedrock melted. It must be where these ammono beetles are coming from now.”

  “It’s like our CELSS farm.”

  “On a gigantic scale… Oh.”

  The mist in the air was lifting. And in the east — beyond a horizon obscured by that immense artifact — Saturn was rising.

  Saturn was autumn brown, against the green sky. Perhaps a quarter hemisphere showed. Time seemed to have been kind to the huge planet: Benacerraf could make out the familiar bands of cloud, tipped up almost vertically towards the ruined sun, and the splashes of white that marked interior-driven storms…

  “The rings,” she said. “Rosenberg, what the hell happened to the rings?”

  The planet’s huge face looked denuded, without that narrow, tilted-up ellipse of banded light, the matching, complex shadows in the cloud tops.

  Rosenberg said, “They were only chunks of ice, Paula. I guess it just got too hot.” He threw down what was left of his mushroom and dusted off his hands. “Let’s go see what’s over the next ridge.”

  He stalked off, eastward. He bounded away, taking big bunny-hops, and was soon fifty yards ahead of her.

  His mood had swung to its manic, energetic pole, she thought gloomily.

  She followed more sedately, trying not to pine for Saturn’s rings.

  The ridge, maybe fifty feet tall, was a pressure wave frozen in the ice, and easy to climb. Rosenberg waited at its crest for her.

  From the crest, the landscape seemed to open up, as the horizon receded to the east. The land beyond the ridge was pretty flat, though in places cracked and compressed.

  At the foot of the ridge there were beetle ammonos, the first she had seen since leaving the plain. They toiled in complex patterns across the barren ice fields here. They made their way in roughly radial patterns to what looked like a jumble of low hillocks at the center of the plateau, neatly sliding over or around the worst crevasses. That cluster of hills was perhaps five miles from them and a half-mile across, or less. The hills thrust irregularly out of the plain, their contours rounded, as if melted, their facets glimmering in the light of Sol and Saturn.