“Here on Titan, outside resources are available to us: water, in the form of bedrock ice, nitrogen and methane from the air, hydrocarbons — like the ethane and propane we can get from Clear Lake — and other compounds, like nitriles and ammonia. That means we can open up some of the loops.”

Benacerraf said, “Water. We’re still recycling every drop we drink. I can taste the six-year-old piss in it, for God’s sake.”

“If we could bring fresh water ice into the system we’d cut down the bulk we’re recycling by forty-five percent. And that would give us a system much better buffered against instabilities.”

“We’re going to have to climb that damn mountain, aren’t we?”

“It’s why we chose to land here, Paula.”

She held her hands up. “I know. It’s just that mountaineering on Titan seems a much dumber idea down here than it did from orbit. What else? What about all those amino acids you say we need?”

Rosenberg scratched his head. “Well, that’s the hole I can’t plug right now. We’ve taken a lot of samples from the air, the diolin slush. No aminos; all I’ve found is the prebiotic organic stuff I expected. If we’re not to be resupplied, there are some trace elements we need as well.”

“So what are the options?”

“We go seek aminos on the surface. Some place we haven’t looked.”

“Like where?”

“The bottom of Clear Lake. Or carbonaceous chondrite craters,” he said.

She turned, looking irritated. “I hate having to ask you to explain all the time, Rosenberg.”

He shrugged. “Then read up. Carbonaceous chondrites are a kind of asteroid. Cratering bodies in this neck of the woods come in four main groups. There are a lot of icy bodies: loose stuff like comet heads, maybe disintegrated moons. Then the M-type asteroids are metallic, metal-rich and dense. The S-types are silicaceous. Rocky. And the C-types are the carbonaceous chondrites. Water, iron, stone and carbon. If we find a carbonaceous chondrite crater we might find kerogen.”

“What’s that?”

“A hydrocarbon. A tarry stuff you find in oil shales. It contains carbon, oxygen, hydrogen, sulphur, potassium, chlorine, other elements…” He smiled. “It’s the nearest thing to a nutritional broth we’re likely to find out here. Mom’s condensed primordial soup.

You know, we can reach a lot of craters with the skimmer, when we set it up,”

“All right. When we fix the skimmer, we’ll discuss it. What else?”

What else, what else…

As the session went on, Rosenberg started to feel hunted, as if everything was coming back to him. Questions, questions. What if he got an answer wrong? It is too much for one person, he thought, this responsibility for all our lives.

But he did his best to answer Paula’s questions.

When Paula had gone, he stayed in his seat and stared out into Titan’s twilit gloom.

Benacerraf felt pressured as well, of course. Rosenberg just came up with options; Benacerraf had to make decisions about them.

But all the time they were skirting around the biggest issues. There was the problem of Angel, for one thing. And the real limiting factor to their chances of survival, here on Titan: not water, not amino acids, but energy.

The run-down of the Topaz suite was the final limiting factor, even if they could bridge all the other gaps in the loops. When the power faded below some critical threshold, the cold was going to get them at last.

Rosenberg had no plans, no ideas, how to get over that.

Rosenberg was the smartest person on the whole damn moon. If he couldn’t figure a way out of this, nobody was going to. And then he would die. And not at some remote, far-future date, but here, on this crappy moon, and soon. All of this — the orbiter, Apollo, their neat little gadgets and improvised tools — all of it would still be here, but his spark of consciousness, his unique self, would be gone. It would be like a shell, slowly decaying, presumably buried for good in the drifting slush in a couple of hundred years. Eventually, there would be no sign he’d even existed.

That was unbearable to Rosenberg. He’d come here, in some vague way, to find the future, to find answers, to do science. To escape Earth. But now, this. There had to be a way out of this trap, the abandonment by NASA, the dwindling resources, the cold…

Beyond the tholin-streaked windows of the flight deck, the gloomy slush-covered ground of Titan stretched off to an orange-stained, concealed horizon. In all the world that Rosenberg could see, under a brown-black lid of a cloudy sky, only a handful of human artifacts — the bundles of equipment under yellow parachute fabric, the stained white conical walls of Bifrost — showed any color other than the universal murky orange-brown.

He closed his eyes, for a few seconds.

Then he got up, and went back to work.

Later, Rosenberg went out again, to help Benacerraf in her efforts to deploy the skimmer.

The skimmer — properly, the TGEV, the Titan Ground Effect Vehicle — was a fifty-million-dollar improvisation, put together by Boeing, at Seattle, in under eighteen months. Right now it was still folded up in its palette on the side of the orbiter like a construction toy. Benacerraf had it halfway out, like an aluminum dragonfly struggling to emerge from its chrysalis. Rosenberg helped her haul on the lanyards.

Abruptly the main fuselage sections locked, and four legs popped out at the corners, telescopic tubes with wide orange footpads. With a couple more hauls, they had the skimmer unfolded, and set upright on the surface.

Rosenberg — sweating inside his suit, pulled muscles aching — walked slowly around the craft.

Sitting on its spidery legs the skimmer was a spindly, open-frame box built around a ducted fan, with a skirt of flexible metal mesh draped around its base. The fan’s housing curved upwards above the center of the craft, a shaped funnel. There were two metal-framed couches in front of the fan, each big enough to accommodate a suited crew member, and there was a simple control box with a joystick in front of the left-hand seat.

Inside the fan housing there was a rotor blade, designed to push the thick Titan air down through the duct and into the skirt, so providing the hovercraft effect that would lift the skimmer off the ground. The fan was run off series-wound electric motors, powered by two big silver-zinc batteries that could be recharged from the Topaz.

The frame was shaved-thin aluminum, to save weight. The skimmer carried its own navigation computer, communications system and cargo space for maps, samples, tool-racks, spare battery. There was even a fold-out tent, so that astronauts could spend a night away from Discovery on an extended EVA.

It was a sophisticated piece of equipment. But the skimmer, with its umbrella antennae and fold-up seats, looked in the light of his helmet lamp as if it had come out of someone’s hobby shop. Like some backyard Victorian inventor’s dream of space travel.

With her hand in Rosenberg’s, Benacerraf climbed up into the left hand seat. She was maybe four feet off the ground; the duct mouth flared above her like a huge crown. She dug a reference card out of a slip pocket, and began throwing switches.

Suddenly bulbs sparkled over the framework, green and red and white, with big, down-pointing floods that splashed light over the gumbo.

“Wow,” said Rosenberg. “It looks like a Christmas tree.”

Benacerraf said, “I think—”

There was a noise from the duct, a whump-whump that carried easily to Rosenberg through the thick air. Rapidly, the rotor increased its speed, and the noise smoothed out to a whir.

From beneath the skirt, a thin sheet of gumbo blasted out across the ground in all directions. It was like a paint-sprayer; it took only seconds for Rosenberg’s legs, almost up to his waist, to be coated in crap.