‘Life?’ Poole asked, boyishly excited once more.
Miriam said, ‘It looks like it, doesn’t it?’ Without warning, she loosened one hand from the net, grabbed at one of the tubes and dragged it away from its hold on the wall. It wriggled in her hand, pale and sightless, a fat worm; its front end, open like a mouth, was torn.
‘Ugh,’ I said. ‘Throw it back!’
But Miriam was cradling the thing. ‘Oh, I’m sorry. I hurt you, didn’t I?’
Poole bent over it. ‘Alive, then.’
‘Oh, yes. And if it’s surviving in this ammonia lava, I wouldn’t mind betting it’s a cousin of whatever’s down below in the sea. More life, Michael!’
‘Look, I think it’s been browsing on the ice. They are clustered pretty thickly over the walls.’
And when I looked, I saw he was right; there the tube-fish were, nibbling away, working their way slowly up the vent.
Poole speculated, ‘Maybe they actively keep the vent open?’ He took a small science box from Miriam’s pack, and there, together – even as we rode that alien’s back down into the throat of the volcano – they briskly analysed the beast’s metabolism, and the contents of the water we were immersed in, and sent the results back to the Hermit Crab. Even Harry’s Virtual head popped up before us, grinning inanely, in that extreme situation.
I had seen enough. With a snap, I made my suit turn its lights off. I had no desire to sit shivering in the dark as invisible ice walls plummeted past me. But I was gambling that curiosity would get the better of Poole and Miriam, and I was right; soon it was Poole whose suit glowed, spending his own precious power to light me up, as they laboured over their pointless science.
At length they came to some conclusion. ‘So I was right,’ Miriam breathed at last. ‘This vent, and the mantle ocean, host a whole other domain – a third on Titan, in addition to the silanes and the CHON sponges. Ammono life . . .’
The moon’s liquid mantle is thought to be a relic of its formation, in a part of the solar nebula where ammonia was common.
Titan was born with a rocky core and a deep ocean, of water laced with ammonia. The ocean might have stayed open for a billion years, warmed by greenhouse effects under a thick primordial atmosphere. A billion years is plenty of time for life to evolve. Eventually the ocean surface froze over to form an icy crust, and at the ocean’s base complex high-pressure forms of ice formed a deep solid layer enclosing the silicate core. Ice above and below, but still the liquid ocean persisted between, ammonia-rich water, very alkaline, very viscous. And in that deep ocean had emerged a unique kind of life, adapted to its strange environment, based on chemical bonds between carbon and nitrogen-hydrogen chemical groups rather than carbon-oxygen, using ammonia as its solvent rather than water: ‘ammono life’, the specialists call it.
‘Yes, a third kind of life,’ Miriam said. ‘One unknown elsewhere in the Solar System so far as I know. So here on Titan you have a junction of three entirely different domains of life: native ammono life in the mantle ocean, CHON life in the crater lakes blown in from the inner System, and the silane lilies wafting in from Triton and the outer cold. Incredible.’
‘More than that,’ Harry said tinnily. ‘Michael, that tube-fish of yours is not a methanogen – it doesn’t create methane – but it’s full of it. Methane is integral to its metabolism, as far as I can see from the results you sent me. It even has methane in its flotation bladders.’
Miriam looked at the tube-fish blindly chewing at the ice walls. ‘Right. They collect it somehow, from some source deep in the ocean. They use it to float up here. They even nibble the cryovolcano vent walls, to keep them open. They have to be integral to delivering the methane from the deep ocean sources, up through the crevices in the ice cap and to the atmosphere. So you have the three domains not just sharing this moon but cooperating in sustaining its ecology.’
Harry said, ‘Quite a vision. And as long as they’re all stupid enough, we might make some money out of this damn system yet.’
Miriam let go of her tube-fish, like freeing a bird; it wriggled off into the dark water. ‘You always were a realist, Harry.’
I thought I saw blackness below us, in the outer glimmer of Poole’s suit lamps. I called, ‘How deep is this ice crust, before we get to the mantle ocean?’
‘Around thirty-five kilometres,’ Harry replied.
‘And how deep are we now?’
‘Oh, around thirty-five kilometres.’
Michael Poole gasped. ‘Lethe. Grab hold, everybody.’
It was on us at once: we had almost passed through this vent we had followed all the way down from the cryovolcano mouth at the surface, this passage right through the ice crust of Titan. I gripped the net and shut my eyes.
The spider let go of the wall and dropped into the void. As we passed out of the vent, through the roof of ice and into the mantle beneath, I felt the walls recede from me, a wash of pressure, a vast opening-out. And we fell into the dark and the cold.
12
Now that the walls were gone from under its limbs I could feel that the spider was swimming, or perhaps somehow jetting, ever deeper into that gloopy sea, while the three of us held on for our lives.
Looking up I saw the base of Titan’s solid crust, an ice roof that covered the whole world, glowing in the light of Poole’s lamps but already receding. And I thought I saw the vent from which we had emerged, a much eroded funnel around which tube-fish swam languidly. Away from the walls I could more easily see the mechanics of how the fish swam; lacking fins or tails they seemed to twist through the water, a motion maybe suited to the viscosity of the medium. They looked more like bloated bacteria than fish.
Soon we were so far beneath the ice roof that it was invisible, and we three and the spider that dragged us down were a single point of light falling into the dark.
And then Poole turned off his suit lamps!
I whimpered, ‘Lethe, Poole, spare us.’
‘Oh, have a heart,’ Miriam said, and her own suit lit up. ‘Just for a time. Let him get used to it.’
I said, ‘Get used to what? Falling into this endless dark?’
‘Not endless,’ Poole said. ‘The ocean is no more than – how much, Harry?’
‘Two hundred and fifty kilometres deep,’ Harry said, mercifully not presenting a Virtual to us. ‘Give or take.’
‘Two hundred and fifty . . . How deep are you intending to take us, Poole?’
‘I told you,’ Michael Poole said grimly. ‘As deep as we need to go. We have to retrieve that GUTengine, Emry. We don’t have a choice – simple as that.’
‘And I have a feeling,’ Miriam said bleakly, ‘now we’re out of that vent, that we may be heading all the way down to the bottom. It’s kind of the next logical choice.’
‘We’ll be crushed,’ I said dismally.
‘No,’ Harry Poole piped up. ‘Look, Jovik, just remember Titan isn’t a large world. The pressure down there is only about four times what you’d find in Earth’s deepest oceans. Five, tops. Your suit is over-engineered. Whatever it is that kills you, it won’t be crushing.’
‘How long to the bottom, then?’
Harry said, ‘You’re falling faster than you’d think, given the viscosity of the medium. That spider is a strong swimmer. A day, say.’
‘A day!’
Miriam said, ‘There may be sights to see on the way down.’
‘What sights?’
‘Well, the tube-fish can’t exist in isolation. There has to be a whole ammono ecology in the greater deeps.’
My imagination worked overtime. ‘Ammono sharks. Ammono whales.’