Titan n-2

by Stephen Baxter

  As time eroded, the logic of physics unfolded implacably. The sun was no longer young. Its core became denser and hotter, as it clogged with the accumulated helium ash of billions of years’ hydrogen fusion. The sun got brighter, at the rate of eight percent per billion years.

  But for a long time Earth’s surface temperature remained the same. Earth was protected by matter and energy feedback cycles maintained by living and geological processes. And as the temperature rose silicate rocks weathered more easily, absorbing carbon dioxide from the atmosphere.

  But it couldn’t last forever.

  Eventually the carbon dioxide concentration in the atmosphere fell so low that the plants and trees could no longer photosynthesize. That put an end to the biosphere’s carbon supply. The rocks continued to weather, and the carbon dioxide concentration fell still more rapidly, and Earth heated quickly.

  Maybe humans could have prevented this, with some huge feat of planetary engineering. There were no humans around to try.

  On the parched planet, one species after another faced what human biologists had called thermal barriers to their survival. The more complex plant and animal species diminished first, as Earth shed the biological complexity painfully gained over billions of years.

  After a billion and a half years the surface temperature averaged fifty degrees Centigrade, above which no animal, fish, crustacean or insect could survive. Most vascular plants and mosses succumbed as well, leaving the land and oceans empty save for micro-organisms: multi-celled animals like algae and fungi.

  But above sixty or seventy degrees the structural characteristics of even the simplest multi-celled creatures — like membrane systems — could not be sustained. The survivors now were one-celled creatures, like cyanobacteria and some photosynthetic bacteria.

  Above seventy degrees photosynthesis ceased at last.

  The last survivor of Earth’s once-rich biosphere was a hardy bacterium, swimming through the sulphur-rich waters surrounding a black smoker ocean-floor vent. The story of life on Earth had come full circle, for the heat-loving archaebacteria were among the oldest life forms: they had arisen on a younger, hotter Earth, and become the progenitors of all subsequent life.

  The end came at two hundred and fifty degrees Centigrade, above which the very stuff of life — the giant molecules, nucleic acids and ammo acids — was broken down.

  After another hundred million years the oceans began to boil.

  Huge clouds of vapor were suspended in the atmosphere. A new greenhouse factor came into play, driving temperatures higher still, ever faster.

  The water clouds did not last long. The water vapor was broken up by energetic sunlight and its hydrogen was driven off into space, leaving a planet baked permanently free of water.

  And the loss of all water stopped the weathering of silicate rock, the process which drew carbon dioxide out of the atmosphere. Volcanic carbon dioxide began to accumulate in the atmosphere. New clouds rose, and the planet began to bake…

  At that remote time, Venus and Earth became at last what humans had dreamed in ancient times: twin planets, alike in every significant detail — scorched dry, their surfaces cracked and flattened under a dense, sluggish atmosphere, utterly lifeless.

  It was different, for Titan.

  The heating of the sun ruined the old surface of Titan, the gumbo-streaked, icy landscape humans had explored. The ethane of Clear Lake boiled, evaporated. The gases dissolved there — nitrogen, methane, hydrogen — thickened the atmosphere still further, adding to a greenhouse effect that accelerated the warming of the atmosphere.

  Eventually the comparatively thin shells of ice over the magma — the ancient ammonia oceans — melted, exposing the primal seas once more. Ammonia and water vapor enriched the air and boosted the greenhouse effect still further.

  It got warm.

  The remnants of ancient biologies stirred. A story of life, interrupted billions of years earlier, was able to resume.

  For a while. But it was a life which would not have long to flourish.

  Soon, the sun neared the end of its stable Main Sequence lifetime; it began its final, deadly bloom.

  When the sun’s core hydrogen was exhausted, the fusion fire there dimmed. For ten million years the core contracted. Then a shell of hydrogen outside the core started to burn. That started the expansion of the outer layers.

  The sun grew gigantic, its surface billowing towards what was left of the inner planets. Confronted by the huge face of the sun, Earth’s surface temperature reached three thousand degrees, only a little less than the surface of the expanding sun.

  Life on Titan shrivelled, baked, as even the water ice bedrock began to melt.

  …Like a desiccated dragonfly corpse adrift on a breeze, Voyager One circled the heart of the Galaxy.

  At last the slow sublimation of metal caused the aluminum structure to weaken to the point where its ten-sided framework collapsed. The fragments of the spacecraft — instrument booms and power generator, pitted and tarnished, metal walls reduced to a paper thickness — drifted away from each other. The directional antenna, as thin as a dried autumn leaf, crumbled away from the curving spars that supported it, so that the ruin of the spacecraft was surrounded by a cloud of glittering aluminum dust.

  Voyager was a fragment of American technology, a thing of metal dug from the vanished Earth, some twenty thousand light years from the sun. It was the last human artifact in existence.

  * * *

  …Rosenberg was lying on his back.

  His eyes were closed. He was warm, comfortable. He was aware of his body — his face, arms, legs were a tangible, solid, massy physical presence — but there was no EVA suit around him, no sleeping bag.

  He seemed to be rising. As if he was in some huge elevator.

  He opened his eyes.

  He was in darkness. He could see only the fuzzy patterns, star-bursts and whorls, generated by the hard-wiring of his own nervous system.

  He could hear nothing.

  Maybe he was in some kind of sensory deprivation tank.

  He tried to remember how he’d got here. He remembered Titan — the Cronos EVA, those damn carrots, Benacerraf nursing him back in Discovery…

  I ought to be dead, he thought.

  Was this some kind of hallucination? Was he still propped up in that lumpy Apollo couch in the hab module, wrapped in Beta-cloth, his senses failing as his body slowly fell apart?

  He felt a stab of panic.

  He reached up to his face. He felt his cheeks, the pressure of his hands, the bones of his nose.

  His cheeks were smooth. Free of stubble. And when he ran his palms up over his face, there wasn’t a hair on his head: no eyebrows, no eyelashes.

  He reached down to his groin. He was naked. His hands cupped his genitals, warm lumps of flesh. No pubic hair.

  He jammed a finger up his left nostril. No hairs there, either.

  Puzzling.

  And, he thought, you’re moving pretty well for a guy in the last stages of Vitamin A poisoning, Rosenberg.

  Anyhow, this was no hallucination. I can feel my balls, therefore I am.

  He dropped his hands to his sides. His hands hit something. It was a soft, pliable floor of what felt like plastic. It seemed to have no temperature, neither hot nor cold.

  He felt to left and right. The floor stretched under him. He could push his fingers an inch or so into the material before he reached the limits of pliability, where it became tough and hard.

  Maybe he was in some kind of bubble.

  He didn’t have enough data to work on. He ought to wait. Maybe he could sleep.

  Sleep, right.

  He tried to control his fear.

  Be logical, Rosenberg. Whoever has brought you here, wherever here is, can’t mean you any harm.

  He ought to separate the world into pieces he could understand. Dismiss the problems he could do nothing about.

  Like, the air. Where was it coming from? How was it replenished?
Was it poisoned?

  Here’s my plan: don’t breathe, until we know more…

  He had to accept the air. He had to accept the temperature, the living conditions.

  Later, he would be hungry, thirsty. He would have to deal with those problems when he could.

  Great logic. He found he’d cupped his hands over his genitals again. A primate reflex, he thought. I’m just a scared monkey, alone in the dark.

  On impulse, he spoke. “Hey.”

  He could hear his voice.

  “Testing, one, two. How about that.” He clapped his hands. He heard no echo, just the dead sound of the clap itself. So, a little more data. This bubble, or rubber room, whatever, was anechoic…

  Something changed.

  There was a light above him, deep crimson, barely visible. The intensity varied as he moved his head from left to right.

  Work it out, Rosenberg. That means the light is external to you. There’s something above, which is differentiated from what is below.

  The light seemed to spread, as if across a flat surface. He thought he could see ripples, scattering oily highlights. Maybe he was rising up through some fluid, towards a meniscus.

  He looked down at himself. He could see his body, emerging in the gathering light, chest and legs stretching away before him, his nipples dark against a hairless chest, a faint landscape of flesh.

  He was bald, but healthy. No sign of the Vitamin A crap that had killed him.

  …The light brightened. Suddenly he was approaching the surface. It was indeed a meniscus, the surface of some body of fluid, and he could see slow, fat ripples, streaks of some scummy deposit—

  The surface broke, in a pulsing circle, directly above him. The fluid spilled down over the hull of his protective bubble.

  He saw a sky. It was high and tall, and scattered with thin, ice-white cirrus clouds. There was a fat red sun — too big — near the zenith, bright enough to dazzle him, surrounded by a fine halo. Contrails criss-crossed the sky.

  That sun really was too damn big, and the sky was a rich blue-green.

  The fluid fell away. The chamber was dimly visible around him, like a soap bubble, in glimmerings of refracted light.

  Rosenberg sat up.

  All around him, beyond his bubble, a solid mass was breaking the liquid.

  The surface was corrugated, and it glistened, deep green. And as it rose, he could see how the platform bulged upwards, a dome perhaps fifty yards across. His filmy bubble perched, squat, on the top of the corrugated dome, as if on the back of some immense turtle.

  Rosenberg got to his knees. He pressed his face and hands flat against the warm surface of his bubble, and stared out.

  The dome, still rising from the liquid, was an island in an oily sea that stretched to the horizon. The fluid wasn’t clear; it was overlaid by a purplish scum, frothing in places. There were a couple of pink-white ice floes, clustering amid the scum islands.

  The air was clear, if green-tinged, and he could see thick, fat ripples proceeding in concentric circles away from the rising mass he rode. Further out there were waves — they looked gigantic, mounds of liquid maybe a hundred feet tall — and they drifted across the sea, driven by the prevailing winds.

  He could see land.

  Perhaps a mile from him, there was a shallow beach; and beyond that, a cliff, steep, grey-green and heavily eroded.

  It could be Cronos, he thought.

  He wanted to try something.

  The bubble was too small to allow him to stand up, but by squatting on all fours he was able to thrust himself up into the air, by a foot or so.

  It took him maybe a half-second to sink back to the floor.

  He tried it a couple more times, before he was satisfied. The gravity here was low, surely no more than a seventh or eighth of a G.

  Right. He was still on Titan. But a Titan that was changed, out of all recognition.

  …And the sun was too big.

  It was the central fact he didn’t want to face.

  It was so big it outsized the fat yellow sun of Earth, let alone the shrunken disc he’d observed at Saturn. And it was a deep, angry red. He thought he could see spots, gigantic black flaws, sprawled across its disc.

  He could only think of one way the sun could have gotten so big, so red.

  By getting old.

  Oh, shit, he thought. I am a long way from home.

  It was all too big, too much. He was a scared, naked primate, stranded in an alien future… He could do a Bill Angel, retreat into some dark primitive recess he’d brought with him, all the way from the past…

  The hell with that. Think, Rosenberg. Categorize.

  He thought about the gravity. The waves.

  All that proved the laws of physics were still working. And he could still figure things out. Even run experiments, test hypotheses. Hang onto that, Rosenberg. Whatever the hell is going on here, science still works. I can figure it out.

  Anyhow, isn’t this what I wanted? To cheat death — to see how it all came out in the end?

  …But, deep down, he had expected some kind of team from Earth to retrieve them, human faces peering over some kind of hospital bed.

  Not this.

  He wanted to curl into a ball, retreat into sleep and incomprehension. But if he did, he might never come back out.

  His shadow, blurred by its passage through the bubble wall, fell over the corrugations, shortened by the high angle of sunlight.

  He tried to feel the corrugations through the bubble material, but the stuff wasn’t flexible enough to give him any real sense of touch. He thought he could see something of a cellular structure, though: there was a crude graininess to the corrugations, lumps maybe the size of rice grains. Cells, maybe. The surface looked almost porous, where he could see it closely. There were beads of some liquid gathered there, and a crusty, solid deposit…

  I bet that solid’s cyanogen. His mind raced. This is some kind of animal.

  Ammonia life?

  Come on, Rosenberg, you know the theory. His huge steed must drink ammonia, respire by burning methane in nitrogen. But cyanogen, the carbon dioxide analogue, was a solid at these temperatures. And so the hide of this creature was dripping with ammonia, and crusted with cyanogen waste.

  In that case, he thought with growing excitement, he had to be rising out of an ammonia ocean, polluted with complex, melted hydrocarbons. There must be some form of photosynthesis going on here: ammono plants, using solar energy to turn respiration products — ammonia and cyanogen — back to methane and nitrogen, closing the matter loops. But cyanogen could only circulate in solution, not as readily as gaseous carbon dioxide in the air of Earth. That must mean the photosynthesis-analogue was going on in the oceans — some kind of plankton equivalent there. Perhaps there were no land-colonizing plants here…

  Perhaps the creature whose back he rode was the flowering of the ammono-based life forms whose prebiotic chemicals he had glimpsed near Tartarus Base.

  It was as he’d predicted to Benacerraf. It was Titan summer.

  How about that. A hell of a lot to deduce from a few grains of cyanogen, Rosenberg. But it was comforting, hugely so, to be able to figure stuff out. And—

  And the surface under him lurched. His bubble rolled. He tried to grab at the yielding wall but could get no grip. He slid down the wall, his chest rubbing against the soft, warm material, and finished on his front at the base of the bubble.

  The bubble stabilized again. He climbed back up to his knees.

  Beyond the rim of the corrugated surface, the ocean was receding from him rapidly, its oily ripples diminishing, and he could see the reflection of the swollen sun as a disc on the sluggish surface. His bubble sat on the back of a mass of flesh, maybe a hundred yards wide, a big flattened sphere. Those complex bruised-purple corrugations spread all the way to the rim. Maybe the creature needed a lot of surface area, for its bulk.

  He could see a shadow sailing over the ocean surface. It was the shadow of hi
s huge steed. There were ropy objects trailing beneath, maybe tentacles, waving passively in reaction to the breeze of the flight…

  The shadow was under him. The damn thing was flying, now, like some immense chewed-up balloon. He was riding a jellyfish the size of a football field, as it flew through the green air of a new Titan…

  Wonder battled with fear, threatening to overwhelm him. He longed to be enclosed: he longed for the cozy warmth of his EMU, the tight metal walls of the hab module.

  …So how was it flying? He couldn’t see any wings, jets, propellers.

  Anti-gravity?

  Think, Rosenberg. Look for the simple explanation.

  The thing was probably buoyant. Simple gas-bags, somewhere within this fat structure, would be sufficient to lift the jellyfish from the ocean, and up into Titan’s thick air.

  There was something else riding the back of the jellyfish, about twenty yards from him.

  It was another bubble, resting like a drop of water on the back of the ammono creature.

  He threw himself at the wall of his translucent cage and stared across. It was like trying to see inside a droplet of scummy pond water.

  He thought he saw something in there, an inert white form.

  He shouted, banging on the wall of his bubble. He even tried to roll forward, within the bubble, to make the whole thing roll across the jellyfish, like a hamster in a plastic ball. But the bubble resisted his efforts.

  His mind seemed to dissolve. To hell with the red giant sun, the new biosphere. All he wanted was to reach that other human being.

  He was soon panting, his hairless flesh coated with a sheen of sweat.

  He gave up.

  Even if he’d got over to the other bubble there wasn’t anything he could have done to reach its occupant. If he could somehow breach this bubble — even if the temperatures outside were tolerable — the air of this new Titan was surely toxic, laced with hydrogen cyanide and ammonia.

  But it was sure as hell worth a try.

  He was finding it harder to breathe.

  He felt an uncomfortable pressure in his bladder. He needed to take a piss.