The soles of Rosenberg’s feet had split, each of them, down the middle: almost neatly, like the soles of cheap shoes. The casts of dead skin came away like plastic moulds in her hands, leaving roughened, raw tissue, from which a watery fluid leaked.

“Dear God, Rosenberg.”

He whispered, “It’s not as bad as it looks.”

“What the hell is wrong with you?”

His head lolled, and he sighed, his voice a rattle.

“You know, don’t you?”

His head rolled around until he was facing her. “Yes, I know what it is. I think, anyhow. You need to take a few blood samples to—”

“Tell me.”

“Vitamin A poisoning. Those damn baby carrots.” He opened his mouth to laugh, and spittle looped between his lips. “Remember, Paula? They were too bitter for you. Well, you were right. More vitamin A than dog liver. Another failure of this toy ecosystem we’re trying to maintain here. No buffering… the whole thing’s too small… levels of toxin all over the place. We just couldn’t control it well enough. We gave it a good try, but it was going to get us in the end…”

There was a flap of skin, loose, beneath his ear. Like a ring-tab, she thought. With a sense of dread, she touched it. It was dry. She pulled at it.

The epidermal covering of Rosenberg’s ear came away intact, a complete cast. It drooped between her finger and thumb. “Oh, Jesus Christ.” She shivered violently and flung the thing away.

He fell against her, clutching at her arm. “You have to get the samples in, Paula. Look for the kerogen. Do it while I can help you. Everything depends on that — everything—”

His head lolled again, and he went limp.

Gently, she tucked her arms under his body, and lifted him like a child.

There had been no signal from the ground, of any kind. Benacerraf checked every day, and bounced test signals off Cassini, to ensure there was no fault with the satellite. And she sent transmissions home, regular updates, with their results, and some personal messages.

In case anyone was listening.

The choice was not to send at all, and that would have felt like giving up. Or as if, by her own loss of faith, by not acting as if there was someone left down there, she might actually somehow bring down the catastrophe they both feared.

She could picture Seattle, almost as vividly as if she was there. She could picture the house where she’d grown up, the places she’d lived with Jackie as a child, her grandchildren… It was more real, to her, than this murky shit-hole.

How could it be gone, ruined? How could there be nobody, walking the dog, watching the news, mowing the lawn?

In the privacy of her room, though, she grieved, little by little, for her family. It was as if she was allowing herself to face the huge loss, piece by piece.

What she feared most was the thought that she and Rosenberg might be all that was left. She hated the idea that her actions, the rest of her trivial life, had suddenly become so significant.

She wished she had some way to climb up above the clouds, to lash up some kind of telescope and peer at the Earth, and see.

Rosenberg sat on a Command Module couch. He was wrapped up, pupa-like, in layers of clothing and thick blankets of Beta-cloth, but he still complained about feeling cold. He wore heavy sunglasses — they’d belonged to Bill Angel — to protect his eyes from the glare of the hab module floods. He’d lost most of his hair, and much of the skin from his scalp and face; swathes of raw tissue showed where his flesh was exposed, riddled by crimson crevasses.

Benacerraf made herself a meal: rice, boiled in Titan melt, with lettuce and some beef jerky from the stores. She sat opposite Rosenberg as she ate. She’d already fed him tonight, spooning the contents of one of their last soup sachets into his mouth, trying not to react to the blood and hunks of loose skin that followed the spoon back out of his lips.

Rosenberg had become the defining feature in her mental landscape now, as so much of her time was given over to caring for him: medical attention, tending to his basic needs — wiping my ass,as Rosenberg put it — and covering his work for him.

He told her what he’d found in the samples from El Dorado. His voice was a thin, robotic rasp.

“I found a lot of interesting products. Beyond the usual organic sediments that come from the stratospheric chemistry, there are traces of urea, organic acids, diacids, some amino acids. Products of tholin hydrolysis. Other amino acids resulting from cyanogen addition to nitriles. Results of cyanogen and nitrile polymerization, including imidazole, purines, pyrimidines. I got aldehydes, ketones, acetaldehyde — the results of alkyne hydrolysis. Some Strecker synthesis — aldehyde-nitrile condensation. Aldehyde polymers, including sugars, glycerol, some other species of—”

“Christ, Rosenberg. Did we find kerogen or not?”

“…No,” he said. “I’m sorry, Paula. I guess I was wrong; El Dorado can’t hare been a carbonaceous chondrite crater after all. My best guess now is that it was formed by a fragment, a calving of a much bigger bolide, which was probably water ice… There is a large water ice crater system a little further to the west.” His head rolled back and forth. “And that’s recent. Maybe the impact was in historic times. Maybe it could have been visible from Earth through a telescope, if anyone had been looking that way, a giant ice comet smashing into Titan… A hell of a thing.”

“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 Earth-like 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.”