"But that's the point," Poole said testily, as if I had challenged his manhood. "We're here under the noses of your curators' sensors, Emry. The less of a splash we make the better."

Miriam Berg said, "I designed this part of the mission profile. We're going to float around at this alt.i.tude, about eight kilometers up-well above any problems with the topography but under most of the cloud decks. We ought to be able to gather the science data we need from here. A couple of weeks should be sufficient."

"A couple of weeks in this suit!"

Poole thumped the walls of the gondola. "This thing expands. You'll be able to get out of your suit. It's not going to be luxury, Emry, but you'll be comfortable enough."

Miriam said, "When the time comes we'll depart from this alt.i.tude. The Crab Crab doesn't carry an orbit-to-surface flitter, but Harry will send down a booster unit to rendezvous with us and lift the gondola to orbit." doesn't carry an orbit-to-surface flitter, but Harry will send down a booster unit to rendezvous with us and lift the gondola to orbit."

I stared at her. "We don't carry the means of getting off this moon?"

"Not on board, no," Miriam said evenly. "Ma.s.s issues. The need to stay under the curacy sensors' awareness threshold. We're supposed to look like an unmanned probe, remember. Look, it's not a problem."

"Umm." Call me a coward, many have. But I didn't like the idea that my only way off this wretched moon was thousands of kilometers away, and depended on a complicated series of rendezvous and coupling manoeuvres. "So what's keeping us aloft? Hydrogen, helium?"

Poole pointed at that inlet pipe. "Neither. This is a hot air balloon, Emry, a Montgolfier." And he gave me a lecture on how hot-air technology is optimal if you must go ballooning on t.i.tan. The thick air and low gravity make the moon hospitable for balloons, and at such low temperatures you get a large expansion in response to a comparatively small amount of heat energy. Add all these factors into the kind of tradeoff equation men like Poole enjoy so much, and out pops hot-air ballooning as the low-energy transport of choice on t.i.tan.

Miriam said, "We're a balloon, not a dirigible; we can't steer. But for a mission like this we can pretty much go where the wind takes us; all we're doing is sampling a global ecosphere. And we can choose our course to some extent. The prevailing winds on t.i.tan are easterly, but below about two kilometers there's a strong westerly component. That's a tide, raised by Saturn in the thick air down there. So we can select which way we get blown, just by ascending and descending."

"More stealth, I suppose. No need for engines."

"That's the idea. We've arrived in the local morning. t.i.tan's day is 15 Earth days long, and we can achieve a lot before nightfall in fact I'm intending that we should chase the daylight. Right now we're heading for the south pole, where it's summer." And there, as even I knew, methane and ethane pooled in open lakes the only stable such liquid bodies in the System, save only for those on Earth and Triton.

"Summer on t.i.tan," Poole said, and he grinned. "And we're riding the oldest flying machine of all over a moon of Saturn!" Evidently he was starting to enjoy himself.

Miriam smiled back, and their gloved hands locked together.

The envelope snapped and billowed above us as the warm air filled it up.

VI Landfall

So we drifted over t.i.tan's frozen landscape, heading for the south pole. For now Michael Poole kept us stuck in that unexpanded hull, and indeed inside our suits, though we removed our helmets, while the crew put the gondola through a fresh series of post-entry checks. I had nothing to do but stare out of the transparent hull, at the very Earthlike clouds that littered the murky sky, or over my shoulder at the landscape that unfolded beneath me.

Now we were low enough to make out detail, I saw that those darker areas were extensive stretches of dunes, lined up in parallel rows by the prevailing wind. The ground looked raked, like a tremendous zen garden. And the lighter areas were outcroppings of a paler rock, plateaus scarred by ravines and valleys. At this lat.i.tude there were no open bodies of liquid, but you could clearly see its presence in the recent past, in braided valleys and the sh.o.r.es of dried-out lakes. This landscape of dunes and ravines was punctuated by circular scars that were probably the relics of meteorite impacts, and by odder, dome-like features with irregular calderas-volcanoes. All these features had names, I learned, a.s.signed to them by Earth astronomers centuries dead, who had eagerly examined the first robot-returned images of this landscape. But as n.o.body had ever come here those names, borrowed from vanished paradises and dead G.o.ds, had never come alive.

I listened absently as Poole and the others talked through their science program. The atmosphere was mostly nitrogen, just as on Earth, but it contained five percent methane, and that methane was the key to t.i.tan's wonders, and mysteries. Even aside from its puzzling central role in the greenhouse effects which stabilized the atmosphere, methane was also key to the complicated organic chemistry that went on there. In the lower atmosphere methane reacted with nitrogen to create complex compounds called tholins, a kind of plastic, which fell to the ground in a sludgy rain. When those tholins landed in liquid water, such as in impact-warmed crater lakes, amino acids were produced the building blocks of our kind of life...

As I listened to them debate these issues it struck me than none of them had begun his or her career as a biologist or climatologist: Poole and Berg had both been physicists, Dzik an engineer and more lately a project manager. Both Berg and Dzik had had specialist training to a decent academic standard to prepare for this mission. They all expected to live a long time; periodically they would re-educate themselves and adopt entirely different professions, as needs must.

I have never had any such ambition. But then, somehow, despite AS technology, I do not imagine myself reaching any great age.

Their talk had an edge, however, even in those first hours. They were all ethically troubled by what they were doing, and those doubts surfaced now that they were away from Harry Poole's goading.

"At some point," Miriam Berg said, "we'll have to face the question of how we'll react if we do we do find sentience here." find sentience here."

Bill Dzik shook his head. "Sometimes I can't believe we're even here, that we're having this conversation at all. I remember exactly what you said on Baked Alaska, Michael. 'The whole System is going to beat a path to our door to see this as long as we can work out a way to protect the ecology... And if we can't, we'll implode the d.a.m.n wormhole. We'll get funds for the Cauchy the Cauchy some other way.' That's what you said." some other way.' That's what you said."

Poole said harshly, clearly needled, "That was 13 years ago, d.a.m.n it, Bill. Situations change. People change. And the choices we have to make change too."

As they argued, I was the only one looking ahead, the way we were drifting under our balloon. Through the murk I thought I could see the first sign of the ethane lakes of the polar regions, sheets of liquid black as coal surrounded by fractal landscapes, like a false-color mock-up of Earth's own Arctic. And I thought I could see movement, something rising up off those lakes. Mist, perhaps? But there was too much solidity about those rising forms for that.

And then the forms emerged from the mist, solid and looming.

I pulled my helmet on my head and gripped my couch. I said, "Unless one of you does something fast, we may soon have no choices left at all."

They looked at me, the three of them in a row around me, puzzled. Then they looked ahead, to see what I saw.

They were like birds, black-winged, with white lenticular bodies. Those wings actually flapped in the thick air as they flew up from the polar seas, a convincing simulacrum of the way birds fly in the air of Earth. Oddly they seemed to have no heads.

And they were coming straight towards us.

Michael Poole snapped, "Lethe. Vent the buoyancy!" He stabbed at a panel, and the others went to work, pulling on their helmets as they did so.

I felt the balloon settle as the hot air was released from the envelope above us. We were sinking but we seemed to move in dreamy slow motion, while those birds loomed larger in our view with every heartbeat.

Then they were on us. They swept over the gondola, filling the sky above, black wings flapping in an oily way that, now they were so close, seemed entirely unnatural, not like terrestrial birds at all. They were huge, each 10, 15 meters across. I thought I could hear could hear them, a rustling, snapping sound carried to me through t.i.tan's thick air. them, a rustling, snapping sound carried to me through t.i.tan's thick air.

And they tore into the envelope. The fabric was designed to withstand t.i.tan's methane rain, not an attack like this; it exploded into shreds, and the severed threads waved in the air. Some of the birds suffered; they tangled with our threads or collided with each other and fell away, rustling. One flew into the gondola itself and crumpled like tissue paper, and then fell, wadded up, far below us.

And we fell too, following our victim-a.s.sa.s.sin to the ground. Our descent from the best part of eight kilometers high took long minutes; we soon reached terminal velocity in t.i.tan's thick air and weak gravity. We had time to strap ourselves in, and Poole and his team worked frantically to secure the gondola's systems. In the last moment Poole flooded the gondola with a foam that filled the internal s.p.a.ce and held us rigid in our seats, like dolls in packaging, sightless and unable to move.

I felt the slam as we hit the ground.

VII Surface

The foam drained away, leaving the four of us sitting there in a row like swaddled babies. We had landed on t.i.tan the way we entered its atmosphere, backside first, and now we lay on our backs with the gondola tilted over, so that I was falling against Miriam Berg, and the cladded ma.s.s of Bill Dzik was weighing on me. The gondola's hull had reverted to opacity so we lay in a close-packed pearly sh.e.l.l, but there was internal light and the various data slates were working, though they were filled with alarming banks of red.

The three of them went quickly into a routine of checks. I ignored them. I was alive. was alive. I was breathing, the air wasn't foul, and I was in no greater discomfort than having Dzik's unpleasant bulk pressed against my side. Nothing broken, then. But I felt a pang of fear as sharp as that felt by that Virtual copy of me when he had learned he was doomed. I wondered if his ghost stirred in me now, still terrified. I was breathing, the air wasn't foul, and I was in no greater discomfort than having Dzik's unpleasant bulk pressed against my side. Nothing broken, then. But I felt a pang of fear as sharp as that felt by that Virtual copy of me when he had learned he was doomed. I wondered if his ghost stirred in me now, still terrified.

And my bowels loosened into the suit's systems. Never a pleasant experience, no matter how good the suit technology. But I wasn't sorry to be reminded that I was nothing but a fragile animal, lost in the cosmos. That may be the root of my cowardice, but give me humility and realism over the hubristic arrogance of a Michael Poole any day.

Their technical chatter died away.

"The lights are on," I said. "So I deduce we've got power."

Michael Poole said, gruffly rea.s.suring, "It would take more than a jolt like that to knock out one of my GUT engines."

Dzik said spitefully, "If we'd lost power you'd be an icicle already, Emry."

"Shut up, Bill," Miriam murmured. "Yes, Emry, we're not in bad shape. The pressure hull's intact, we have power, heating, air, water, food. We're not going to die any time soon."

But I thought of the flapping birds of t.i.tan and wondered how she could be so sure.

Poole started unbuckling. "We need to make an external inspection. Figure out our options."

Miriam followed suit, and laughed. She said to me, "Romantic, isn't he? The first human footfalls on t.i.tan, and he calls it an external inspection."

Bill Dzik dug an elbow in my ribs hard enough to hurt through the layers of my suit. "Move, Emry."

"Leave me alone."

"We're packed in here like spoons. It's one out, all out."

Well, he was right; I had no choice.

Poole made us go through checks of our exosuits, their power cells, the integrity of their seals. Then he drained the air and popped open the hatch in the roof before our faces. I saw a sky somber and brown, dark by comparison with the brightness of our internal lights, and flecks of black snow drifted by. The hatch was a door from this womb of metal and ceramics out into the unknown.

We climbed up through the hatch in reverse order from how we had come in: Poole, Dzik, myself, then Miriam. The gravity, a seventh of Earth's, was close enough to the Moon's to make that part of the experience familiar, and I moved my weight easily enough. Once outside the hull, lamps on my suit lit up in response to the dark.

I dropped down a meter or so, and drifted to my first footfall on t.i.tan. The sandy surface crunched under my feet. I knew it was water ice, hard as gla.s.s. The sand at my feet was ridged into ripples, as if by a receding tide. Pebbles lay scattered, worn and eroded. A wind buffeted me, slow and ma.s.sive, and I heard a low ba.s.s moan. A black rain smeared my faceplate.

The four of us stood together, chubby in our suits, the only humans on a world larger than Mercury. Beyond the puddle of light cast by our suit lamps an entirely unknown landscape stretched off into the infinite dark.

Miriam Berg was watching me. "What are you thinking, Jovik?" As far as I know these were the first words spoken by any human standing on t.i.tan.

"Why ask me?"

"You're the only one of us who's looking at t.i.tan and not at the gondola."

I grunted. "I'm thinking how like Earth this is. Like a beach somewhere, or a high desert, the sand, the pebbles. Like Mars, too, outside Kahra."

"Convergent processes," Dzik said dismissively. "But you are an entirely alien presence. Here, your blood is as hot as molten lava. Look, you're leaking heat."

And, looking down, I saw wisps of vapor rising up from my booted feet.

The others checked over the gondola. Its inner pressure cage had been st.u.r.dy enough to protect us, but the external hull was crumpled and damaged, various attachments had been ripped off, and it had dug itself into the ice.

Poole called us together for a council of war. "Here's the deal. There's no sign of the envelope; it was shredded, we lost it. The gondola's essential systems are sound, most importantly the power." He banged it with a gloved fist; in the dense air I heard a m.u.f.fled thump. "The hull's taken a beating, though. We've lost the extensibility. I'm afraid we're stuck in these suits."

"Until what?" I said. "Until we get the spare balloon envelope inflated, right?"

"We don't carry a spare," Bill Dzik said, and he had the grace to sound embarra.s.sed. "It was a cost-benefit a.n.a.lysis "

"Well, you got that wrong," I snapped back. "How are we supposed to get off this d.a.m.n moon now? You said we had to make some crackpot mid-air rendezvous."

Poole tapped his chest, and a Virtual image of Harry's head popped into existence in mid-air. "Good question. I'm working on options. I'm fabricating another envelope, and I'll get it down to you. Once we have that gondola aloft again I'll have no trouble picking you up. In the meantime," he said more sternly, "you have work to do down there. Time is short."

"When we get back to the Crab" Crab" Bill Dzik said to Poole, "you hold him down and I'll kill him." Bill Dzik said to Poole, "you hold him down and I'll kill him."

"He's my father," said Michael Poole, "I'll kill him." kill him."

Harry dissolved into a spray of pixels.

Poole said, "Look, here's the deal. We'll need to travel if we're to achieve our science goals; we can't do it all from this south pole site. We do have some mobility. The gondola has wheels; it will work as a truck down here. But we're going to have to dig the wreck out of the sand first, and modify it. And meanwhile Harry's right about the limited time. I suggest that Bill and I get on with the engineering. Miriam, you take Emry and go see what science you can do at the lake. It's only a couple of kilometers," he checked a wrist map patch and pointed, "that way."

"OK." With low-gravity grace Miriam jumped back up to the hatch, and retrieved a pack from the gondola's interior.

I felt deeply reluctant to move away from the shelter of the wrecked gondola. "What about those birds?"

Miriam jumped back down and approached me. "We've seen no sign of the birds since we landed. Come on, curator. It will take your mind off how scared you are." And she tramped away into the dark, away from the pool of light by the gondola.

Poole and Dzik turned away from me. I had no choice but to follow her.

VIII Lake

Walking any distance was surprisingly difficult.

The layered heat-retaining suit was bulky and awkward, but it was flexible, and that was unlike the vacuum of the Moon, where the internal pressure forces even the best skin-suits to rigidity. But on t.i.tan you are always aware of the resistance of the heavy air. At the surface the pressure is half as much again as on Earth, and the density of the air four times that at Earth's surface. It is almost like moving underwater. And yet the gravity is so low that when you dig your feet into the sand for traction you have a tendency to go floating off the ground. Miriam showed me how to extend deep, sharp treads from the soles of my boots to dig into the loose sand.

It is the thickness of the air that is the challenge on t.i.tan; you are bathed in an intensely cold fluid, less than 100 degrees above absolute zero, that conducts away your heat enthusiastically, and I was always aware of the silent company of my suit's heating system, and the power cells that would sustain it for no more than a few hours.

"Turn your suit lights off," Miriam said to me after a few hundred meters. "Save your power."

"I prefer not to walk into what I can't see."

"Your eyes will adapt. And your faceplate has image enhancers set to the spectrum of ambient light here... Come on, Jovik. If you don't I'll do it for you; your glare is stopping me seeing too."

"All right, d.a.m.n it."

With the lights off, I was suspended in brown murk, as if under an autumn sky obscured by the smoke of forest fires. But my eyes did adapt, and the faceplate subtly enhanced my vision. t.i.tan opened up around me, a plain of sand and wind-eroded rubble under an orange-brown sky again not unlike Mars, if you know it. Clouds of ethane or methane floated above me, and beyond them the haze towered up, a column of organic muck tens of kilometers deep. Yet I could see the sun in that haze, a spark low on the horizon, and facing it a half-full Saturn, much bigger than the Moon in Earth's sky. Of the other moons or the stars, indeed of the Crab, Crab, I could see nothing. All the colors were drawn from a palette of crimson, orange, and brown. Soon my eyes longed for a bit of green. I could see nothing. All the colors were drawn from a palette of crimson, orange, and brown. Soon my eyes longed for a bit of green.

When I looked back I could see no sign of the gondola, its lights already lost in the haze. I saw we had left a clear line of footsteps behind us. It made me quail to think that this was the only footstep trail on all this little world.

We began to descend a shallow slope. I saw lines in the sand, like tide marks. "I think we're coming to the lake."

"Yes. It's summer here, at the south pole. The lakes evaporate, and the ethane rains out at the north pole. In 15 years' time, half a Saturnian year, it will be winter here and summer there, and the cycle will reverse. Small worlds have simple climate systems, Jovik. As I'm sure a curator would know..."

We came to the edge of the ethane lake. In that dim light it looked black like tar, and sluggish ripples crossed its surface. In patches something more solid lay on the liquid, circular sheets almost like lilies, repellently oily. The lake stretched off black and flat to the horizon, which curved visibly, though it was blurred in the murky air. It was an extraordinary experience to stand there in an exosuit and to face a body of liquid on such an alien world, the ocean black, the sky and the sh.o.r.e brown. And yet there was again convergence with the Earth. This was a kind of beach. Looking around I saw we were in a sort of bay, and to my right, a few kilometers away, a river of black liquid had cut a broad valley, braided like a delta, as it ran into the sea.

And, looking that way, I saw something lying on the sh.o.r.e, crumpled black around a grain of paleness.

Miriam wanted samples from the lake, especially of the discs of gunk that floated on the surface. She opened up her pack and extracted a sampling arm, a remote manipulator with a claw-like grabber. She hoisted this onto her shoulder and extended the arm, and I heard a whir of exoskeletal multipliers. As the arm plucked at the lily-like features some of them broke up into strands, almost like jet-black seaweed, but the arm lifted large contiguous sheets of a kind of film that reminded me of the eerie wings of the t.i.tan birds that had attacked us.

Miriam quickly grew excited at what she was finding.

"Life," I guessed.