Stephen Baxter: Xeelee: Endurance

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.

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 alien 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.