Xeelee: Endurance

by Stephen Baxter

  Their technical chatter died away.

  ‘The lights are on,’ I said. ‘So I deduce we’ve got power.’

  Michael Poole said, gruffly reassuring, ‘It would take more than a jolt like that to knock out one of my GUTengines.’

  Dzik said spitefully, ‘If we’d lost power you’d be an icicle already, Emry.’

  ‘Shut up, Bill,’ Miriam murmured. ‘Yes, Emry, we’re not in bad shape. The pressure hull’s intact, we have power, heating, air, water, food. We’re not going to die any time soon.’

  But I thought of the flapping birds of Titan and wondered how she could be so sure.

  Poole started unbuckling. ‘We need to make an external inspection. Figure out our options.’

  Miriam followed suit, and laughed. She said to me, ‘Romantic, isn’t he? The first human footfalls on Titan, and he calls it an external inspection.’ Suddenly she was friendly. The crash had evidently made her feel we had bonded in some way.

  But Bill Dzik dug an elbow in my ribs hard enough to hurt through the layers of my suit. ‘Move, Emry.’

  ‘Leave me alone.’

  ‘We’re packed in here like spoons. It’s one out, all out.’

  Well, he was right; I had no choice.

  Poole made us go through checks of our exosuits, their power cells, the integrity of their seals. Then he drained the air and popped open the hatch in the roof before our faces. I saw a sky sombre and brown, dark by comparison with the brightness of our internal lights. Flecks of black snow drifted down. The hatch was a door from this womb of metal and ceramics out into the unknown.

  We climbed up through the hatch in reverse order from how we had come in: Poole, Dzik, myself, then Miriam. The gravity, a seventh of Earth’s, was close enough to the Moon’s to make that part of the experience familiar at least, and I moved my weight easily enough. Once outside the hull, lamps on my suit lit up in response to the dark.

  I dropped down a metre, and thus drifted to my first footfall on Titan.

  The sandy surface crunched under my feet. I knew the sand was water ice, grains hard as glass in the intense chill. The sand was ridged into ripples, as if by a receding tide, and pebbles lay scattered, worn and eroded. A wind buffeted me, slow and massive, and I heard a low bass moan. A black rain smeared my faceplate.

  The four of us stood together, chubby in our suits, the only humans on a world larger than Mercury. Beyond the puddle of light cast by our suit lamps an entirely unknown landscape stretched off into the infinite dark.

  Miriam Berg was watching me. ‘What are you thinking, Jovik?’ As far as I know these were the first words spoken by any human standing on Titan.

  ‘Why ask me?’

  ‘You’re the only one of us who’s looking at Titan and not at the gondola.’

  I grunted. ‘I’m thinking how like Earth this is. Like a beach somewhere, or a high desert, the sand, the pebbles. Like Mars, too, outside Kahra.’

  ‘Convergent processes,’ Dzik said dismissively. ‘But you are an entirely alien presence. Here, your blood is as hot as molten lava. Look, you’re leaking heat.’

  And, looking down, I saw wisps of vapour rising up from my booted feet.

  We checked over the gondola. Its inner pressure cage had been sturdy enough to protect us, but the external hull was crumpled and damaged, various attachments had been ripped off, and it had dug itself into the ice.

  Poole called us together for a council of war. ‘Here’s the deal. There’s no sign of the envelope; it was shredded, we lost it. The gondola’s essential systems are sound, most importantly the power. The hull’s taken a beating, though.’ He banged the metal wall with a gloved fist; in the dense air I heard a muffled thump. ‘We’ve lost the extensibility. I’m afraid we’re stuck in these suits.’

  ‘Until what?’ I said. ‘Until we get the spare balloon envelope inflated, right?’

  ‘We don’t carry a spare,’ Bill Dzik said, and he had the grace to sound embarrassed. ‘It was a cost-benefit analysis—’

  ‘Well, you got that wrong,’ I snapped back. ‘How are we supposed to get off this damn moon now? You said we had to make some crackpot rendezvous with a booster pack.’

  Poole tapped his chest, and a Virtual image of Harry’s head popped into existence in mid-air. ‘Good question. I’m working on options. I’m fabricating another envelope, and I’ll get it down to you. Once we have that gondola aloft again, I’ll have no trouble picking you up. In the meantime,’ he said more sternly, ‘you have work to do down there. Time is short.’

  ‘When we get back to the Crab,’ Bill Dzik said to Poole, ‘you hold him down and I’ll kill him.’

  ‘He’s my father,’ said Michael Poole. ‘I’ll kill him.’

  Harry dissolved into a spray of pixels.

  Poole said, ‘Look, here’s the deal. We’ll need to travel if we’re to achieve our science goals; we can’t do it all from this south pole site. We do have some mobility. The gondola has wheels; it will work as a truck down here. But we’re going to have to dig the wreck out of the sand first, and modify it. And meanwhile Harry’s right about the limited time. I suggest that Bill and I get on with the engineering. Miriam, you take Emry and go see what science you can do at the lake. It’s only a couple of kilometres’ – he checked a wrist map patch and pointed – ‘that way.’

  ‘OK.’ With low-gravity grace Miriam jumped back up to the hatch, and retrieved a pack from the gondola’s interior.

  I felt deeply reluctant to move away from the shelter of the wrecked gondola. ‘What about those birds?’

  Miriam jumped back down and approached me. ‘We’ve seen no sign of the birds since we landed. Come on, curator. It will take your mind off how scared you are.’ And she tramped away into the dark, away from the pool of light by the gondola.

  Poole and Dzik turned away from me. I had no choice but to follow her.

  8

  Walking any distance was surprisingly difficult.

  The layered heat-retaining suit was bulky and awkward, but it was flexible, and in that Titan was unlike the Moon with its vacuum, where the internal pressure forces even the best skinsuits to rigidity. But on Titan you are always aware of the resistance of the heavy air. At the surface the pressure is half as much again as on Earth, and the density of the air four times that at Earth’s surface. It is almost like moving underwater. And yet the gravity is so low that when you dig your feet into the sand for traction you have a tendency to go floating off the ground. Miriam showed me how to extend deep, sharp treads from the soles of my boots to dig into the loose sand.

  It is the thickness of the air that is the survival challenge on Titan; you are bathed in an intensely cold fluid, less than a hundred degrees above absolute zero, that conducts away your heat enthusiastically, and I was always aware of the silent company of my suit’s heating system, and the power cells that would sustain it for no more than a few hours.

  ‘Turn your suit lights off,’ Miriam said to me after a few hundred metres. ‘Save your power.’

  ‘I prefer not to walk into what I can’t see.’

  ‘Your eyes will adapt. And your faceplate has image enhancers set to the spectrum of ambient light here . . . Come on, Jovik. If you don’t I’ll do it for you; your glare is stopping me from seeing too.’

  ‘All right, damn it.’

  With the lights off, I was suspended in brown murk. But my eyes did adapt, and the faceplate subtly enhanced my vision. Titan opened up around me, a plain of sand and wind-eroded rock under an orange-brown sky – again not unlike Mars. Clouds of ethane or methane floated above me, and beyond them the haze towered up, layers of organic muck tens of kilometres deep. Yet I could see the sun in that haze, a spark low on the horizon, and facing it a half-full Saturn, much bigger than the Moon in Earth’s sky. Of the other moons or the stars, indeed of the Crab, I could see nothing. All the c
olours were drawn from a palette of crimson, orange and brown. Soon my eyes longed for a bit of green.

  When I looked back I could see no sign of the gondola, its lights already lost in the haze. I saw we had left a clear line of footsteps behind us. It made me quail to think that this was the only footstep trail on all this little world.

  We began to descend a shallow slope. I saw lines in the sand, like tide marks. ‘I think we’re coming to the lake.’

  ‘Yes,’ Miriam said. ‘It’s summer here, at the south pole. The lakes evaporate, and the ethane rains out at the north pole. In time it will be winter here and summer there, and the cycle will reverse. Small worlds have simple climate systems, Jovik. As I’m sure a curator ought to know . . .’

  We came to the edge of the ethane lake. In that dim light it looked black like tar, and sluggish ripples crossed its surface. Patches of something more solid lay on the liquid, circular sheets almost like lilies, repellently oily. The lake stretched off black and flat to the horizon, which curved visibly, though it was blurred in the murky air.

  It was an extraordinary experience to stand there in an exosuit and to face an ocean on such an alien world, the sea black, the sky and the shore brown. And yet there was again convergence with the Earth. This was, after all, a kind of beach. Looking around I saw we were in a sort of bay, and to my right, a few kilometres away, a river of black liquid had cut a broad valley, braided like a delta, as it ran into the sea.

  And, looking that way, I saw something lying on the shore, crumpled black around a grain of paleness.

  Miriam wanted samples from the lake, especially of the plates of gunk that floated on the surface. She opened up her pack and extracted a sampling arm, a remote manipulator with a claw-like grabber. She hoisted this onto her shoulder and extended the arm, and I heard a whir of exoskeletal multipliers. As the arm plucked at the lily-like features, some of them broke up into strands, almost like jet-black seaweed, but the arm lifted large contiguous sheets of a kind of film that reminded me of the eerie wings of the Titan birds that had attacked us.

  Miriam quickly grew excited at what she was finding.

  ‘Life,’ I guessed.

  ‘You got it. Well, we knew it was here. We even have samples taken by automated probes. Though we never spotted those birds before.’ She hefted the lake stuff, films of it draped over her gloved hand, and looked at me. ‘I wonder if you understand how exotic this is. I’m pretty sure this is silane life. That is, based on a silicon chemistry, rather than carbon . . .’

  The things on the lake did indeed look like black lilies. But they were not lilies, or anything remotely related to life like my own. Life of our chemical sort is based on long molecules, with a solvent to bring components of those molecules together. Our specific sort of terrestrial life, which Miriam called ‘CHON life’, after its essential elements carbon, hydrogen, oxygen and nitrogen, uses water as its solvent, and carbon-based molecules as its building blocks: carbon can form chains and rings, and long stable molecules like DNA.

  ‘But carbon’s not the only choice, and nor is water,’ Miriam said. ‘At terrestrial temperatures silicon bonds with oxygen to form very stable molecules.’

  ‘Silicates. Rock.’

  ‘Exactly. But at very low temperatures, silicon can form silanols, which are capable of dissolving in very cold solvents – say, in this ethane lake here. When they dissolve they fill up the lake with long molecules analogous to our organic molecules. These can then link up into polymers using silicon-silicon bonds, silanes. They have weaker bonds than carbon molecules at terrestrial temperatures, but it’s just what you need in a low-energy, low-temperature environment like this. With silanes as the basis you can dream up all sorts of complex molecules analogous to nucleic acids and proteins—’

  ‘Which is what we have here.’

  ‘Exactly. Nice complicated biomolecules for evolution to play with. They are more commonly found on the cooler, outer worlds – Neptune’s moon Triton for example. But this lake is cold enough. The energy flow will be so low that it must take a lo-ong time for anything much to grow or evolve. But on Titan there is plenty of time.’ She let the filmy stuff glide off her manipulator scoop and back into the lake. ‘There’s so much we don’t know. There has to be an ecology in there, a food chain. Maybe the films are the primary producers – an equivalent of the plankton in our oceans, for instance. But where do they get their energy from? And how do they survive the annual drying-out of their lakes?’

  ‘Good questions,’ I said. ‘I wish I cared.’

  She stowed her sample bottles in her pack. ‘I think you care more than you’re prepared to admit. Nobody as intelligent as you is without curiosity. It goes with the territory. Anyhow we should get back to the gondola.’

  I hesitated. I hated to prove her right, that there was indeed a grain of curiosity lodged in my soul. But I pointed at the enigmatic black form lying further along the beach. ‘Maybe we should take a look at that first.’

  She glanced at it, and at me, and headed that way without another word.

  It turned out, as I had suspected, that the crumpled form was a bird. I recalled one hitting our gondola during their assault and falling away; perhaps this was that very casualty.

  It was essentially a block of ice, about the size of my head, wrapped up in a torn sheet of black film. With great care Miriam used her manipulator arm to pick apart the film, as if she was unwrapping a Christmas present. The ice mass wasn’t a simple lump but a mesh of spindly struts and bars surrounding a hollow core. It had been badly damaged by the fall. Miriam took samples of this and of the film.

  ‘That ice lump looks light for its size,’ I said. ‘Like the bones of a bird.’

  ‘Which makes sense if it’s a flying creature.’ Miriam was growing excited. ‘Jovik, look at this. The filmy stuff of the wings looks identical to the samples I took from the surface of the lake. It has to be silane. But the ice structure is different.’ She broke a bit of it open, and turned on a suit lamp so we could see a mass of very thin icicles, like fibres. It was almost sponge-like. Inside the fine ice straws were threads of what looked like discoloured water. ‘Rich in organics,’ Miriam said, glancing at a data panel on her manipulator arm. ‘I mean, our sort of organics, CHON life, carbon-water – amino acids, a kind of DNA. There are puzzles here. Not least the fact that we find it here, by this lake. CHON life has been sampled on Titan before. But it’s thought carbon-water life can only subsist here in impact-melt crater lakes, and we’re a long way from anything like that . . .’

  Her passion grew, a trait I have always found attractive.

  ‘I think this is a bird, one of those we saw flying at us. But it seems to be a composite creature, a symbiosis of these silicon-based wings and the ice lump – silane life cooperating with CHON life! Just remarkable. You wonder how it came about in the first place . . . but I guess there are examples of survival strategies just as intricate in our own biosphere. Give evolution enough time and anything is possible. I wonder what it is they both want, though, what the two sides in this symbiosis get out of the relationship . . .

  ‘It’s a genuine discovery, Jovik. Nobody’s seen this before – life from two entirely different domains working together. And I wouldn’t have noticed it if not for you.’ She held out the ice lump to me. ‘They’ll probably name it after you.’

  Her enthusiasm was fetching, but not that much. ‘Sure. But my concern right now is how much power we have left in these suit heaters. Let’s get back to the gondola.’

  So she stowed away the remaining fragments of the Titan bird, Jovik Emry’s contribution to Solar System science, and we retraced our path back to the gondola.

  9

  The days are very long on Titan, and by the time we got back to the gondola nothing seemed to have changed about the landscape or the sky – not a diffuse shadow had shifted. We found Poole and Dzik, surrounded by alie
n mystery, happily fixing big balloon wheels to axles slung beneath the crumpled hull. Boys will be boys.

  When they were done, we all climbed back aboard. Poole had reset some of the interior lamps so they glowed green, yellow and blue; it was a relief to be immersed once more in bright Earth light.

  We set off in our gondola-truck for the next part of our expedition. We were making, I was told, for an impact crater believed to hold liquid water, which itself was not far from a cryovolcano, another feature of interest for the expedition. This site was perhaps a hundred kilometres from where we had come down.

  Miriam transferred her lake samples to cold stores, and ran some of them through a small onboard science package. She jabbered about what she had discovered. Poole encouraged her more than Dzik did, but even that wasn’t much. Dzik and Poole were more interested at that moment in playing with the gondola. They sat at an improvised driver’s console and fussed over gear ratios and the performance of the big tyres. Poole even insisted on driving the bus himself, though Titan was so flat and dull for the most part he could easily have left the chore to the onboard systems. That proved to me the fallacy of not bringing along specialist biologists on a jaunt like this. It was only Miriam who seemed to have a genuine passion for the life systems we were supposed to be here to study; Dzik and Poole were too easily distracted by the technology, which was, after all, only a means to an end.

  They had, however, rearranged the interior to make it feel a little less cramped. The couches had been separated and set up around the cabin, so you could sit upright with a bit of elbow room. The cabin was pressurised so we could remove our helmets, and though the expandable walls didn’t work any more there was room for one at a time to shuck off his or her exosuit. Poole ordered us to do so; we had already been inside the suits for a few hours, and the suits, and ourselves, needed some down time. Poole had set up a curtained-off area where we could let our discarded suits perform their self-maintenance functions while we had showers – of water recycled from our urine and sweat, which was deemed a lot safer than melt from the ice moon. Poole himself used the shower first, and then Miriam. She was hasty, eager to get back to her work, and kept talking even while she cleaned up.