Titan (76 page)

“So we’re fucked. The EVA was a wild goose chase.”

“All the products I found were the result of reacting Titan materials with water from the bolide. I’m sorry, Paula.”

She grunted. “It was a good shot. Anyhow, I didn’t have any smarter ideas.”

He seemed to be trying to lean forward; he struggled, feebly, within his Beta-cloth layers. “Look, Paula. We have to face facts. We’re beyond rescue from Earth. We’re on our own here. We ought to look at the worst case.”

“The worst case?” She laughed, around a mouthful of rice. “Look at us, Rosenberg. What could be worse than this?”

“We are the last humans.”

He fell silent, his breathing a noisy rasp.

She felt the motion of her jaw slow, without conscious volition. Saliva pooled in her mouth, flooding the rice grains and lettuce there, swamping her sense of taste.

Rosenberg said, “The great unspoken truth, huh.”

Deliberately she started to chew again; she swallowed a mouthful of saliva.

“But what difference does it make?” she said. “We’re fucked anyhow.”

“True. Without the kerogen supplement, our ecosystem isn’t going to last long. A couple more system crashes and we won’t be able to recover. We just aren’t viable here. We tried hard to make it so, but in the long term we were always going to lose. And the whole thing will die with the two of us anyhow.”

“Right,” she said brutally. “So what does it matter? Rosenberg, Earth is a billion miles away. We could try to eke out our lives up here for years, or we could blow up the damn Topaz today. So what? It makes no difference, except to ourselves.”

“You’re wrong, Paula,” he whispered, his ruined mouth gaping open. “I’ll tell you what difference it makes. We’re still part of Earth’s biosphere, even if we are a little seed pod transplanted across a billion miles. Even here, we’re still connected; in fact, we have a greater responsibility.
We might be all that’s left
. You and I as individuals are going to die here. But what we do before then might determine the future of Earthlike life in the Solar System. We have a responsibility, Paula.”

She stared at him. “You’re crazy, Rosenberg,” she said bluntly. “You’re such a pompous asshole. Everybody’s dead, except us, and we have no resources at all, and here you are talking about the destiny of life.”

His cracked lips spread in a grin. “I have a plan.”

“You and your plans, Rosenberg.”

“I think I know a place where we can find liquid water…”

The surfaces of all Saturn’s moons had been shaped by impacts. Titan’s surface had been shielded by its thick blanket of atmosphere, but its huge mass had acted to focus impacting objects onto itself.

Thus, there were impact craters all over Titan.

“Paula, think about a pool of impact melt at the bottom of a crater, dug into Titan ice, heated by the kinetic energy of the impact. It cools down to the freezing point, and stays there at constant temperature—zero degrees—as it freezes and shrinks. It can only lose heat by thermal conductivity. It’s a slow process. The conduction equations are well understood. And water is good at retaining heat…”

“It will stay liquid.”

“A crater a hundred miles across might have an impact melt pool ten miles wide. And it would take ten thousand years to freeze.”

She frowned. “So if the crater beyond El Dorado, the primary that spawned the smaller crater we found, is only a few hundred years old—”

“It should contain a pool of liquid water. With a concentration of organics of a few parts in a thousand…”

“Holy shit, Rosenberg.”

“Yeah. That’s not all. What about impact ejecta?” Ejecta was material thrown out after an impact, through the explosive decompression of the shocked solid surface. “On the Moon, ejecta is thrown out into a near-vacuum, and it’s a mixture of vapor and solid. But on Titan, with its thick atmosphere, you’ll have something more like the cratering process on Venus. Ejecta will flow in blankets over the surface, to three or four times the crater width, and maybe a hundred yards deep. And there will be a lot of organic-containing sediments mixed in with the surface ejecta flow. You can calculate the cooling lifetime using heat conduction partial differential equations which—”

“Cut to the chase, Rosenberg.”

“Yeah. There will be ponds of liquid water, maybe a hundred yards deep, scattered over the surface around the primary crater. Even they should last for centuries, maybe longer. They’ll freeze over, of course; so will the impact melt pool at the heart. It will have a thin crust of ice, but will be liquid beneath. With time, as the layer of liquid water shrinks, it will become more concentrated in organics, and you’ll get a whole spectrum of reactions: amino acids, aldehydes and ketones, nucleotide bases… In those pools, we should find an emulation of nearly all the prebiotic chemical pathways on the early Earth, except for the steps involving phosphates… Damn, damn.”

“What?”

“If only we’d gone a little further. I might have found it all, just waiting under the surface, a thin crust of ice. Just waiting for a seed.”

“Waiting for a… Oh.” Suddenly, she saw his plan. “You’re kidding.”

“No.” His sunglasses slipped down over his bony nose. His eyes were blue rocks in the crusty red mass of his face. “Paula, I’ll show you what to do. I made notes in my softscreen. You have to go back to Cronos again. Go further than we did before. Find the primary crater beyond El Dorado, and the impact melt pool at its center. Or maybe you’ll find ejecta ponds. Liquid water, Paula. I’ll prepare a package—”

“What kind of package?”

“Earth-origin microbes that can metabolize tholin.”

“We don’t have the facilities for genetic engineering.”

“We don’t need to engineer them,” he snapped. “Don’t tell me my job, Paula.”

“I’m sorry.”

“I’m talking about common soil bacteria. Aerobic and anaerobic…
Clostridium, Pseudomonas, Bacillus, Micrococcus…
They are present in our nutrient solutions in the farm. They can extract their carbon and nitrogen requirements from tholin…” He started coughing, big spasms that racked his body inside its Beta-cloth shroud. “Drop them in that liquid-water soup of prebiotic organics and they’ll thrive… Earth life, surviving on Titan…” He coughed again.

She stood before him. “Rosenberg, maybe you ought to rest. I’ll clean you up.”

“No.” His eyes were still steady, despite the shuddering of his body “I have to be sure you understand. The responsibility.”

“I know” She knelt before him and put her hand on his bony arm. “Responsibility for the future of Earth’s biosphere. All on your shoulders. I understand, Rosenberg,” she said gently. “But—” “But what?”

“I still don’t get it. Even if I find the ponds, even if I seed them, they’re just going to freeze over, in a few hundred or a thousand years.”

“Sure.”

“So what’s the point?”

He shuddered. “Things will change. In time—billions of years, Paula—the sun will reach the end of its life. It will become a red giant… And then, for a time, Titan will be as warm as the Earth. Titan summer. Maybe our bacterial spores will give rise to a new evolutionary sequence. You see?”

She pulled back from him. Suddenly she felt chilled. “You think big, Rosenberg.”

“Little packets of bacteria… Seed the planets, the comets. If you’re serious about spreading life to other worlds, that’s how you’d do it. Cheap, too. It’s absurd to carry humans around … all that plumbing…” His eyes closed, the big broken lids sweeping down like curtains.

She picked him up, and carried him to the hygiene station.

S
itting on the floor
of the hab module, a Beta-cloth blanket thrown over them both, she cradled him. His head felt huge in her lap, the massive skull with its paper-thin covering of flesh and skin, but his body was feather-light.

He whispered: “How can I die? How can the world keep turning without me? I’m unique, Paula. The center of the universe. The one true sentient individual in an ocean of shapes and noises and faces. How can I die? It’s a cruel joke.”

Dear Rosenberg. Analytical to the end.

“They’ll remember you for coming to Titan. A member of the first expedition. That’s one hell of a memorial.”

“If there is anyone left to remember. Anyhow, even so, I’ll just be a freak in a circus show.”

She said gently, “No god waiting for you, Rosenberg?”

He tried to laugh. He whispered, “What do you think? God died in 1609, when Galileo raised his telescope to the Moon, and saw seas and mountains. We flew to Titan. But with that one act Galileo discovered the Universe. God can’t share the same cosmos as a Moon like that.”

“No,” Benacerraf said sadly. “No, I don’t suppose He can. But where does that leave us, Rosenberg?”

“Fucked,” he said brutally “Science is a system of knowledge, Paula. Not a comfort.”

“I know,” she said. She stroked his forehead, and crooned her words, as if to a sick child. “I know.”

He gripped her arm with a clawlike hand. “Paula. You have to put me through the SCWO.”

“Sure, Rosenberg.”

“I mean it. You can’t afford to waste the biomass. But freeze yourself, Paula. Go out on the ice, when… It’s important…”

He coughed, but even that had lost its vigor. The color seemed to be draining from his face, even from the exposed tissue there, as if his blood was drawing back to the core of his body.

His head rolled on its spindle of neck across her lap. “You know, I’m not afraid. I thought I would be. I’m not.”

She squeezed his hand; it felt as if his bones were grinding together. “You don’t need to be afraid, Rosenberg. I’m here.”

He said, with a spark of sour energy, “It isn’t that. The human stuff, monkeys holding hands against the dark. I never thought that would make any difference. And I was right. But you and I—”

He coughed, and shuddered; his ruined eyes fluttered closed.

She leaned over, closer to his bleeding mouth.

“You and I, with what we’re doing here, are the most important humans who ever lived. We will cast a shadow across five billion years. And that’s a hell of a thing,” he whispered. “A hell of a thing.”

He relaxed, with a rattling sigh, and lay still, collapsing into her arms with a slow-motion, low-gravity calmness. “You know, I learned a lot,” he whispered. “More than I expected.”

“You did good, Rosenberg.”

“But you know, I never figured out why…”

“What?”

“Why did it
feel
like this?”

She could feel his body settle, the internal organs relaxing and losing their tension; the last gases escaped from his stomach in a long, low fart.

She got him into the frigid ground only an hour later.

The grave was just a shallow ditch, scraped out of the gumbo, already infilling. His naked body lay at its base, thin, skeletal, glistening with the frozen water ice of his body.

Once again she had to find words to say over a corpse.

She checked her transmission link to
Cassini.
She wanted this moment to be sent to Earth. Maybe there was somebody there to listen; maybe not. If there was, maybe this would somehow help them.

“I’m sorry I didn’t have a flag to wrap you in, Rosenberg,” she said. “Anyhow, I know this was what you wanted, in spite of what you said. And if you think I was going to have your sorry ass circulating around
my
ecosystem, you got another think coming.

“Casting a shadow across five eons.
Maybe you will at that. You did good, Rosenberg.”

I guess that will do, she thought.

She threw a handful of Othrys ice crystals into the grave, and began to drag her snowshovel over the gumbo, filling in the shallow pit.

I
n the last days she
spent a lot of time in the CELSS farm, trying to stabilize it as much as she could. She kept power supplied to the farm, and left it seeded with a new crop, of wheat, barley and lettuce.

She felt a great responsibility for the drawn, etiolated little plants here. They were, after all, the only living things other than herself on this whole moon, and she felt loyal to them, and regretted she was abandoning them to die.

But there wasn’t much she could do for them. She figured the CELSS farm might last without human intervention a few weeks, before a pump broke down, or a nutrient pipe clogged, or a short burned out half the lamps, or some runaway feedback biocycle caused the miniature ecology to crash.