“How do you know?”

“Because this place is so damn cold. The black-body temperature here will be closer to nine hundred degrees, when the giant phase reaches its climax…”

“Shit.”

“Yeah. The atmosphere will evaporate first. Then the ice mantle will melt, and boil away. Nothing left but the rocky core.”

“How long?”

He shrugged. “I’d say we have a hundred thousand years.”

“A hundred thousand years. Not much.”

He grunted around a mouthful of mushroom. “Only twice as long as the human species existed before we were born. You just don’t think big enough, Paula.”

“No. Hell, I guess I never did. So,” she said. “What are we supposed to do now?”

“I guess that’s up to us. We could try to talk to the ammonos. You know, I’ve been thinking about why we’re here.”

“You have?”

“Yeah. Think about it. They terraformed their own planet. They rebuilt our biosphere, or a copy of it, from what we left behind, as best they could. And they found us in the ice, and managed to… repair us. But I don’t think they understand what we are. They don’t react to us, except as some kind of animal, and they’ve made no attempt to communicate with us. Paula, they might not even know we’re intelligent. Yes, talking to the ammonos would be a hell of a challenge.” He looked up. “Maybe they could tell us what happened to Earth, to mankind. Maybe I could make a telescope. Grind some ice into lenses. It would be interesting to see what else is out there.”

“What else?”

“We could fly here.”

“We could?”

“The light gravity, the thick air… Da Vinci flying machines would work.” He frowned. “Maybe some kind of winged bicycle would be the best solution. Hell, it would be easy. You could glide most of the way. I’ve seen it done. And then we could think about making our own methane rockets. Maybe we could even borrow some of the ammonos’ technology. Paula, this is a moon, but a big damn moon. We can explore it from pole to pole…”

After a time, Benacerraf sat back. “Plans and schemes. Busy, busy, busy. But what’s it for?”

“Huh?”

“Rosenberg, this isn’t some dumb camping trip. It’s not even an EVA. We’re the last survivors of the human race, stuck here in the far future. Are we supposed to repopulate the planet?”

He coughed, spraying out mushroom. “Sorry,” he said, wiping fragments off their joined suits. “I wasn’t expecting that. I sure as hell am no Adam.”

“And I ain’t no Eve,” she said firmly.

Anyhow, the phrase reminded her uncomfortably of Bill Angel.

“I don’t think we need to,” Rosenberg said. “I think I know what that rocket ship is for.”

“It’s pretty damn small,” she said.

“Huh? The rocket?” He looked puzzled. “Small for what?”

“For an evacuation. Titan is doomed, right? But you wouldn’t get a single ammono beetle in that thing.”

He laughed. “You’re thinking like a human, Paula.”

“What do you expect?”

“That’s not a human artifact. And what lies behind it isn’t a human motivation. You have to learn to think like an ammono. We’re dealing here with a race who, when confronted with the destruction of their world, retreated into their worldhouse, and rebuilt their moon to accommodate us. Terrestrial life. Can you imagine humans doing the same?”

“What are you saying?”

“I’m saying these guys think big. Bigger than we ever did. But in a different way. I think they are trying to save their biosphere. And ours. But they’re doing it the way we should have done it. And could have, if anybody had provided the funding.” He looked up at the sun’s diseased face. “But we weren’t smart enough, Paula. We blew it. We dropped a fucking rock on ourselves. We lost ten billion years. We might have covered the Galaxy by now. But we blew it.”

“I think we did okay, Rosenberg,” she said gently. “We’re here, aren’t we? We came to Saturn, and in the end, we found something wonderful. And if you’re right, because of us, Earth life is going to live on, to survive even the death of the sun… Do you think this is what it was all about? All those millennia of struggling, the whole bloody human story, just to deliver the two of us, here, to the end of time…?”

The light around her changed. She looked up, to the east. The sun, a broad, ruddy disc, was descending towards Saturn’s limb. The grand, slow eclipse had started, she saw, with a perfectly circular arc of darkness bitten out of the sun’s swollen face, and red sunlight glimmering around the rim of Saturn, the layers of atmosphere there. She thought she could see the shadow of Saturn sweeping like a wing across the plains of Cronos towards her, and the air grew dark and subdued. She thought she could see a fine, glittering line stretching up towards the zenith: perhaps the remnants of the rings.

…Hey, Paula. Scuttlebutt from home. Some double-dome from JPL is saying he’s found life on Titan…

Benacerraf could feel the elemental human warmth of Rosenberg’s bare skin, all along her flank, from shoulder through hip to ankle.

They planned further.

Today they should try again to build a fire, she said. With a fire they could warm themselves, heat up some water, maybe try cooking some of the vegetable life and see if that improved its flavour.

And beyond that they ought to think about a shelter. Maybe they could construct some kind of log cabin from the wood-analogue of the trees here. But it might prove difficult to cut the wood. Ripping off small branches for a fire was one thing; carpentry for a serious construction would be something else, without metals to work into tools.

Rosenberg started talking longer term. There might be metals to be extracted, from meteorites embedded in craters in the ice…

To the east, over the shadowed ruins of Xi City, white rocket light flared.

EPILOGUE

The mirror array drifted through the rubble of what had been Saturn’s ring system, the ruddy light of bloated Sol casting sharp highlights from its structure. The array was a hundred yards long. Six cup-shaped mirrors, each a yard across, were spaced along a spider-web boom.

The mirrors were pointed away from Sol. The array was looking for planets, of other stars.

For three months now, it had maintained its focus on a young blue-white star, as bright as any in the sky: twenty-seven light years from Sol, fifty times as luminous as Sol in its remote heyday. The six mirrors gathered the star’s scattered photons and focused them on a single collector.

The design was subtle. The collector operated in the infra-red part of the spectrum, where planets shone most brightly. Even so, the star was still millions of times brighter than any planet; but light waves arrived at the six mirrors slightly out of phase and cancelled each other out, allowing planetary light to shine through.

The images formed were ghostly, faint, building up layer by layer.

There proved to be twelve major planets in the new system: three gas giants, the rest rocky or icy worlds. Of the smaller worlds, two lay in the habitable zone for Earth-like life — seven times as far as Earth from Sol — and one lay further out, in a region which might support ammono-like life.

The subtle collectors, slow and persistent and patient, detected spectroscopic traces of atmospheric gases: carbon dioxide, oxygen, water, ammonia, methane.

These worlds, it was decided, were valid targets.

The sail spread like a flower, its silvered surface capturing blood-red pools of sunlight.

It was five hundred yards across. The payload at its heart, a mere two hundred pounds, was a small, black pod.

The probe would not carry much on-board intelligence. The only passengers were microscopic life forms, engineered either for Earth-like conditions, or for Titan summer.