“You think it’s some kind of machine?”

“No. I think it’s alive. It’s an ammono creature. The coloration, the ridging on its back: all of that’s characteristic of the aboriginal life forms here.”

“How do you know?”

“I saw them, remember. Anyhow, you can see for yourself. Look at that blanket over the main body.”

“What is that, some kind of insulation?”

“No. Look at the frost; the temperatures in there must be low enough to allow ammonia to be liquid. Don’t you get it, Paula? It’s a spacesuit. The warming sun has brought the end of the world to Titan as much as to Earth. Now, this ammono animal is forced to take an EVA on the surface of its own planet.”

“So what’s it doing with my turds?”

“Sampling. Come on.” He struggled up to a kneeling position, and the last of their night’s warmth and musk dissipated. “Let’s get out of here.”

They shucked off the bag. Rosenberg pulled the suite apart, and Benacerraf hopped over the chill ground to a clump of trees, where she took a leak.

When she got back to Rosenberg, shivering, she found herself covering up her breasts and crotch until he’d helped her into her reassembled suit. It was odd, but she felt more embarrassed about her nudity in front of the thing Rosenberg had called an ammono than she had before Rosenberg.

The suit sealed up neatly around her, and warmed rapidly.

The two of them walked out of the little copse, and onto the plain. The ammono stayed behind, still sawing industriously at Benacerraf’s crap.

On the open plain, little had changed since the day before. The plain was just a gently sloping tundra, studded by the clusters of low bushes and scratchy grass, bordered at one side by the white cliffs of ice, and on the other by the black, oily, placid sea.

But now, there was movement — delicate, precise — everywhere.

The ammonos were scattered over the plain, from cliff to ocean’s edge. There had to be hundreds of them. And they all looked identical to the table-shaped creature which had disturbed them: the swathe of translucent blanket over the rectangular, ridged carapace, the spindly legs, the arms industriously scratching at the soil.

“They can’t all be taking samples of our dung.”

“Of course not,” he said, faintly irritated. “It isn’t us alone they’re interested in. It’s the whole of this biosphere.”

“Why? What’s the point?”

He pointed east towards the cliffs. “Come on. That way.”

“Why?”

“For one thing, that’s where the ammonos are coming from.”

She looked more carefully. Rosenberg was right. There was a greater density of the ammonos in the direction of the base of the cliffs.

“And for another—” He pointed upwards.

There was a contrail in the sky, white and sharp and unmistakable, scratched across the orange sky. It was rising up out of the east, from the land beyond the ice cliffs.

They walked.

She looked down on the ammonos as she passed them. It was like walking through a field of huge beetles. She could hear the soft clattering of the ammonos’ claws as they worked, a gentle sound like the click of cutlery on plates at some quiet restaurant. The ammonos dug blades of grass, complete little plants, out of the ground. They took black buds from the trees, pulling them gently away from their branches, and plucked seed packets from flowers. They seemed to be trying to avoid damaging the life forms.

When an ammono walked, its limbs would straighten out. Then icicle legs would ripple around the rim, flashing pink highlights, their motion too complex to follow. The table-top body of the ammono would glide evenly over the surface, through seven or eight yards, until it found another place to sample.

Actually, the ammonos hardly ever moved.

Only one in a hundred would be in motion at any time, save for the delicate clatter of limbs; this scattered herd of them together was almost stationary, eerily so, their Zen-like stillness quite unlike the chaotic jostling of terrestrial creatures.

She remarked on this to Rosenberg.

He grunted. “Paula, chemical reactions are dependent on temperature. By the time you get to the region where ammonia is a liquid — under thirty degrees below zero — you’re looking at a relative rate of maybe a hundred to a thousand times as slow as at room temperature for us—”

“You’re saying these creatures have a slower metabolic rate.”

“Much slower, yeah. You can see it in the way they move: those long periods of gathering energy, then a quick burst of motion. But it’s not going to be as simple as that, of course… reactions with the right activation energies won’t chill out, so they would be selected preferentially. And all that ammonia will have a complex effect, helping or hindering reactions. The only way to know for sure would be to take one of those critters apart, and see what’s sloshing about inside its carapace.”

That suggestion offended her.

She bent to pick a flower. “Maybe we shouldn’t be asking questions.”

“Huh?”

“Here we are at the end of time. Everybody we knew — everything we understood — is long gone. What does science, figuring things out, matter now? These ammonos seem to have given us a place we can live. Maybe we ought to be content with that.”

He laughed. “If my forebrain had an off-switch, I’d agree with you.”

She dropped the flower and walked on.

When she looked back, after a few paces, an ammono had crawled laboriously over to the flower and was picking it apart with its scalpel-sharp claw.

They took breakfast on the hoof. Benacerraf tore off handfuls of mushroom flesh and washed it down with water from an ice-flecked brook they found. She splashed water mixed with snow over her face and scalp; the cold was sharp and refreshing. One good thing about being hairless, she thought: at least it was going to be easier to keep clean.

As she walked on, her breath steaming ahead of her, she started to warm up. Soon she had to pull open the seams at her shoulders to keep cool. But the suit must be porous; it wasn’t trapping excessive amounts of heat and sweat.

“Somebody remade Titan, Rosenberg. Engineered it so we could live here. Breathe the air, eat the fruit. Who? People?”

“No. I think it was the ammonos, after the sun got too hot for them, and they had to retreat. Titan ice is primordial stuff, Paula. It probably contains dissolved carbon dioxide, ammonia, methane, organic molecules, sulphur, salts. When it melted it must have out-gassed volatiles. Good for building a new atmosphere.”

“Volatiles I can understand. But this is an ice moon. Where did the topsoil come from?”

“Any particulate matter in the ice would settle out, as dirt on the sea beds. Maybe the ammonos dredged that up. Hell, I don’t know.”

“They, Rosenberg? Why did they do all this? Why are we here, for Christ’s sake?”

He had no answer.

As they neared the base of the horizon-spanning cliffs, the ground began to slope upwards and grew harder and colder underfoot. The topsoil was sparser than on the lowland plain, the vegetation struggling to get a foothold, although there were still clumps of tough dune-like grass struggling out of cracks in the ice bedrock.

Soon it became more of an effort for Benacerraf to continue her steady Moonwalk bound over the surface.

There were fewer ammonos here; in their shining transparent suits they trooped, in their reptilian spurts, back and forth, evidently shuttling between the plain and some kind of base on the Cronos plateau.

A wind blew up, pushing parallel to the cliff face and across their path. Clouds shouldered across the sky: fat cumulus clouds of water vapor, just like Earth’s. And then a rain began to fall, big fat heavy drops that descended with a snowlike slowness, and splashed noisily against her golden-brown suit.