Godlike Machines (18 page)

“So I was right,” Miriam breathed at last. “This vent, and the mantle ocean, host a whole other life domain-
a third
on Titan, in addition to the silanes and the CHON sponges. Ammono life ...”

Titan’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 open ocean, of water laced with ammonia. The ocean might have persisted for a billion years, warmed by greenhouse effects under a thick primordial atmosphere. A billion years is plenty of time for life to evolve. With time 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 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 solute rather than water: “ammono life,” the specialists call it.

“Yes, a third domain,” Miriam said. “One unknown elsewhere in Sol 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 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. “You always were a realist, Harry.”

I thought I saw blackness below us, in the outer glimmer of Poole’s suit lamps. “Harry. How deep is this ice crust, before we get to the mantle ocean?”

“Around 35 kilometers.”

“And how deep are we now? Can you tell?”

“Oh, around 35 kilometers.”

Michael Poole gasped. “Lethe. Grab hold, everybody.”

It was on us almost at once: the base of the vent we had followed all the way down from the cryovolcano mouth at the surface, a passage right through the ice crust of Titan. I gripped the net and shut my eyes.

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 cold.

XII

Ocean

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 they 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 vast bacteria than fish.

Soon we were so far beneath the ice roof that it was invisible, and we three and the crab that dragged us down were a single point of light falling into the dark. And 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?”

“250 kilometers deep,” Harry said, mercifully not presenting a Virtual to us. “Give or take.”

“250 ... How deep are you intending to take us, Poole?”

“I told you,” Michael Poole said grimly. “As deep as it takes. We have to retrieve that GUT engine, 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.”

Miriam laughed. “Sluggish as hell, in this cold soup. And besides, they couldn’t eat you, Jovik.”

“They might spit me out after trying.” I tried to think beyond my immediate panic. “But even if we survive-even if we find our damn GUT engine down there on the ice—how are we supposed to get back?”

Poole said easily, “All we need to do is dump our ballast and we’ll float up. We don’t need to bring up the GUT engine, remember, just use it to recharge the suits.”

Miriam said, “A better option might be to hitch a ride with another spider.”

“Right. Which would solve another problem,” Poole said. “Which is to find a cryovolcano vent to the surface. The spiders know the way, evidently.”

Harry said, “And even if the spiders let you down, I could guide you. I can see you, the vent mouths, even the GUT engine. This neutrino technology was worth the money it cost. There’s no problem, in principle.”

At times I felt less afraid of the situation than of my companions, precisely because of their lack of fear.

Miriam fetched something from a pack at her waist, I couldn’t see what, and glanced at Poole. “Novak’s not going to survive a descent lasting a day. Not in the dark.”

Poole looked at me, and at her. “Do it.”

“Do what?”

But I had no time to flinch as she reached across, and with expert skill pressed a vial into a valve in the chest of my exosuit. I felt a sharp coldness as the drug pumped into my bloodstream, and after that only a dreamless sleep, cradled in the warmth of my cushioned suit.

So I missed the events of the next hours, the quiet times when Poole and Miriam tried to catch some sleep themselves, the flurries of excitement when strange denizens of Titan’s ammono deep approached them out of the dark.

And I missed the next great shock suffered by our strange little crew, when the base of Titan’s underground ocean, an ice floor 300 kilometers beneath the surface, at last hove into view. The strange landscape of this abyssal deep, made of folded high-pressure ices littered by bits of meteorite rock, was punctured by vents and chasms, like an inverted mirror image of the crust far above us.
And the spider we rode did not slow down.
It hurled itself into one of those vents, and once more its limbs began to clatter down a wall of smooth rock-ice.

Harry warned Miriam and Poole that this latest vent looked as if it penetrated the whole of this inner layer of core-cladding ice—Ice VI, laced by ammonia dihydrate—a layer another 500 kilometers deep. At the base of this vent there was only Titan’s core of silicate rocks, and there, surely, the spiders’ final destination must lie.

There was nothing to be done but to endure the ride. It would take perhaps a further day. So Poole and Miriam allowed the spider to drag us down. More tube-fish, of an exotic high-pressure variety, grazed endlessly at the icy walls. Miriam popped me another vial to keep me asleep, and fed me intravenous fluids. Harry fretted about the exhaustion of our power, and the gradual increase of pressure; beneath a column of water and ice hundreds of kilometers deep, we were approaching our suits’ manufactured tolerance. But they had no choice to continue, and I, unconscious, had no say in the matter.

When the ride was over, when the spider had at last come to rest, Miriam woke me up.

I was lying on my back on a lumpy floor. The gravity felt even weaker than on the surface. Miriam’s face hovered over me, illuminated by suit lamps. She said, “Look what we found.”

I sat up. I felt weak, dizzy-hungry. Beside me, in their suits, Miriam and Poole sat watching my reaction. Then I remembered where I was and the fear cut in.

I looked around quickly. Even by the glow of the suit lamps I could not see far. The murkiness and floating particles told me I must be still immersed in the water of Titan’s deep ocean. I saw a roof of ice above me—not far, 100 meters or so. Below me was a surface of what looked like rock, dark and purple-streaked. I was in a sort of ice cavern, then, whose walls were off in the dark beyond our bubble of light. I learned later that I was in a cavern dug out beneath the lower icy mantle of Titan, between it and the rocky core, 800 kilometers below the icy plains where I had crash-landed days before. Around us I saw ice spiders, toiling away at their own enigmatic tasks, and bits of equipment from the gondola, chopped up, carried here and deposited. There was the GUT engine! My heart leapt; perhaps I would yet live through this.

But even the engine wasn’t what Miriam had meant. She repeated, “Look what we found.”

I looked. Set in the floor, in the rocky core of the world, was a hatch.

XIII

Hatch

They allowed me to eat and drink, and void my bladder. Moving around was difficult, the cold water dense and syrupy; every movement I made was accompanied by the whir of servomotors, as the suit labored to assist me.

I was reassured to know that the GUT engine was still functioning, and that my suit cells had been recharged. In principle I could stay alive long enough to get back to the
Hermit Crab.
All I had to do was find my way out of the core of this world, up through 800 kilometers of ice and ocean ... I clung to the relief of the moment, and put off my fears over what was to come next.

Now that I was awake, Michael Poole, Miriam Berg, and Virtual Harry rehearsed what they had figured out about methane processing on Titan. Under that roof of ice, immersed in that chill high-pressure ocean, they talked about comets and chemistry, while all the while the huge mystery of the hatch in the ground lay between us, unaddressed.

Harry said, “On Earth 95 percent of the methane in the air is of biological origin. The farts of animals, decaying vegetation. So could the source be biological here? You guys have surveyed enough of the environment to rule that out. There could in principle be methanogen bugs living in those ethane lakes, for instance, feeding off reactions between acetylene and hydrogen, but you found nothing significant. What about a delivery of the methane by infalling comets? It’s possible, but then you’d have detected other trace cometary gases, which are absent from the air. One plausible possibility remains .. .”

When Titan was young its ammonia-water ocean extended all the way to the rocky core. There, chemical processes could have produced plentiful methane: the alkaline water reacting with the rock would liberate hydrogen, which in turn would react with sources of carbon, monoxide or dioxide or carbon grains, to manufacture methane. But that process would have been stopped as soon as the ice layers plated over the rock core, insulating it from liquid water. What was needed, then, was some way for chambers to be kept open at the base of the ice, where liquid water and rock could still react at their interface. And a way for the methane produced to reach the ocean, and then the surface.

“The methane could be stored in clathrates, ice layers,” Harry said. “That would work its way to the surface eventually. Simpler to build vents up through the ice, and encourage a chemoautotrophic ecosystem to feed off the methane, and deliver it to higher levels.”

“The tube-fish,” I said.

“And their relatives, yes.”

Looking up at the ice ceiling above me, I saw how it had been shaped and scraped, as if by lobster claws. “So the spiders keep these chambers open, to allow the methane-creating reactions to continue.”

“That’s it,” Michael Poole said, wonder in his voice. “They do it to keep a supply of methane pumping up into the atmosphere. And they’ve been doing it for billions of years. Have to have been, for the ecologies up there to have evolved as they have—the tube-fish, the CHON sponges, the silanes.
This whole world is an engine
, a very old engine. It’s an engine for creating methane, for turning what would otherwise be just another nondescript ice moon into a haven, whose purpose is to foster the life forms that inhabit it.”

“And where there is an engine, there are engineers,” Miriam said.

“Yes. But why did they build all this?”

None of them could answer that.

“Ha!” I barked laughter. “Well, the why of it is irrelevant. The spiders are clearly sentient—or their makers are. You have found precisely what you were afraid of, haven’t you, Michael Poole? Sentience at the heart of Titan. You will never be allowed to open it up for exploitation now. So much for your commercial ambitions!”

“Which you were going to share in,” Harry reminded me, scowling.

I sneered. “Oh, I’d only have wasted the money on drugs and sex. To see you world-builders crestfallen is worth that loss. So what’s under the hatch?”