Xeelee: Endurance

by Stephen Baxter

  Poole touched a panel above his head, and the hull turned transparent. Now it was as if we four in our couches were suspended in space, surrounded by glowing instrument panels, and blocky masses that must be the power supply, life support, supplies. Above me the Crab slid across the face of Saturn, GUTdrive flaring, and below me the orange face of Titan loomed large.

  I whimpered. I have never pretended to be brave.

  Miriam Berg handed me a transparent bubble-helmet. ‘Lethe, put this on before you puke.’

  I pulled the helmet over my head; it snuggled into the suit neck and made its own lock.

  Bill Dzik was evidently enjoying my discomfort. ‘You feel safer in the suit, right? Well, the entry is the most dangerous time. But you’d better hope we get through the atmosphere’s outer layers before the hull breaches, Emry. These outfits aren’t designed to work as pressure suits.’

  ‘Then what use are they?’

  ‘Heat control,’ Michael Poole said, a bit more sympathetic. ‘Titan’s air pressure is fifty per cent higher than Earth’s, at the surface. But that thick cold air just sucks away your heat. Listen up, Emry. The gondola’s small, but it has a pretty robust power supply – a GUTengine, in fact. You’re going to need that power to keep warm. For short periods your suit will protect you; there are power cells built into the fabric. But you won’t last more than a few hours away from the gondola. Got that?’

  I was hardly reassured. ‘What about the entry itself? Your father said we’ll follow an unmanned profile. That sounds . . . vigorous.’

  Bill Dzik barked a laugh. Nobody else replied.

  Poole and the others began to work through pre-entry system checks. Harry murmured in my ear, telling me that fresh identity backups had just been taken of each of us and stored in the gondola’s systems. I was not reassured.

  I lay helpless, trussed up and strapped in, as we plummeted into the sunlit face of Titan.

  5

  Fifteen minutes after cutting loose from the Crab, the gondola encountered the first wisps of Titan’s upper atmosphere, thin and cold, faintly blue all around us. Still a thousand kilometres above the ground, I could feel the first faltering in the gondola’s headlong speed. Titan’s air is massive and deep, and I was falling backside first straight into it.

  The first three minutes of the entry were the worst, as we plunged into the air with an interplanetary velocity, and our speed was reduced violently. Three hundred kilometres above the surface the deceleration peaked at sixteen gravities. Cushioned by Poole’s inertial field I felt no more than the faintest shaking, but the gondola shuddered and banged. Meanwhile a shock wave preceded us, a cap of gas that glowed brilliantly: Titan air battered to plasma by the dissipating kinetic energy of the gondola.

  This fiery entry phase was mercifully brief. But when it was over, still we fell helplessly. After another three minutes we were within a hundred and fifty kilometres of the surface, and immersed in an orange haze, the organic-chemistry products of the destruction of Titan’s methane by sunlight. Poole tapped a panel, and a mortar fired above us, hauling out a pilot parachute a couple of metres across. This stabilised us in the thickening air, our backs to the surface, our faces to the sky. Then the main parachute unfolded, spreading reassuringly.

  For fifteen minutes we drifted, sinking slowly into a deep ocean of cold, sluggish air. Poole and his colleagues worked at their slates, gathering data from sensors that measured the physical and chemical properties of the atmosphere. I lay silent, curious too, but frightened for my life.

  As we fell deeper into the hydrocarbon smog the temperature fell steadily. Sixty kilometres above the surface we fell through a layer of cloud into clearer air beneath, and then, at forty kilometres, through a thin layer of methane clouds. The temperature was close to its minimum here, at only seventy degrees or so above absolute zero. Soon it would rise again. As Poole and his team had discussed, greenhouse effects from the mysterious methane that shouldn’t have been there warm Titan’s air all the way to the ground.

  Fifteen minutes after its unpacking, the main parachute was cut away, and a smaller stabiliser canopy opened. Much smaller. We began to fall faster, into the deep ocean of air. ‘Lethe,’ I said. ‘Why did we dump the big chute? We’re still forty kilometres high!’

  Bill Dzik laughed at me. ‘Don’t you know anything about the world you’re supposed to be guarding, curator? The air’s thick here, and the gravity’s low, only a seventh of Earth normal. Under that big parachute we’d be hanging in the air all day . . .’

  The gondola lurched sideways, shoved by the winds. At least that shut Dzik up. But the winds eased as we fell further, until the air was as still and turgid as deep water. We were immersed now in orange petrochemical haze, though the sun was plainly visible as a brilliant point source of light, surrounded by a yellow-brown halo. The crew gathered data on the spectra of the solar halo, seeking information on aerosols, solid or liquid particles suspended in the air.

  And, gradually, beneath our backs, Titan’s ground became visible. I twisted around to see. Cumulus clouds of ethane vapour lay draped over continents of water ice. Of the ground itself I saw a mottling of dark and white patches, areas huge in extent, pocked by what looked like impact craters, and incised by threading valleys cut by flowing liquid, ethane or methane. The crew continued to collect their science data. An acoustic sounder sent out complex pulses of sound. Miriam Berg showed me how some echoes came back double, with reflections from the surfaces and bottoms of crater lakes, like the one my sampling probe had entered.

  The gondola rocked beneath its parachute. Poole had suspended the inertial shielding, and, swinging in Titan’s one-seventh gravity, I was comfortable in my thick, softly layered exosuit. The crew’s murmuring as they worked was professional and quiet. I think I actually slept, briefly.

  Then there was a jolt. I woke with a snap. The parachute had been cut loose, and was drifting away with its strings dangling like some jellyfish. Our fall was slow in that thick air and gentle gravity, but fall we did!

  And then, as Bill Dzik laughed at me again, a new canopy unfurled into the form of a globe, spreading out above us. It was a balloon, perhaps forty, fifty metres across; we were suspended from it by a series of fine ropes. As I watched a kind of hose snaked up from beneath the gondola’s hull and pushed up into the mouth of the balloon, and it began to inflate.

  ‘So that’s the plan,’ I said. ‘To float around Titan in a balloon! Not very energetic for a man who builds interplanetary wormholes, Poole.’

  ‘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 altitude, about eight kilometres 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 coffin!’

  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 climb back up to space from this altitude. The 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.’

  I stared at her. ‘You’re saying we don’t carry the means of getting off this moon?’

  Miriam said evenly, ‘Mass issues. We need to stay under the curacy sensors’ awareness threshold. Plus 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
kilometres away, and my access to it 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 Titan. You have the buoyancy of the thick air, and the gravity is weak, and at such low temperatures you get a large expansion of your heated gas in response to a comparatively small amount of energy. Add all these factors into the kind of trade-off equation men like Poole enjoy so much, and out pops hot-air ballooning as the low-energy transport of choice on Titan.

  Miriam said, ‘We’re a balloon, not a dirigible; we can’t steer. But for a mission like this it’s enough for us to go pretty much 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 Titan are easterly, but below about two kilometres there’s a strong westerly component. That’s actually 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. Titan’s day is fifteen 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 at the summer pole, as even I knew, methane and ethane pooled in open lakes – the only stable bodies of surface liquid in the System, aside from those on Earth and Triton.

  Poole grinned. ‘Summer on Titan. And we’re riding the oldest flying machine of all!’ 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.

  6

  So we drifted over Titan’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 through the transparent walls at the very Earthlike clouds that littered the murky sky, or over my shoulder at the landscape that unfolded beneath me.

  Now that 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 latitude there were no open bodies of liquid, but you could clearly see its presence in the recent past, in braided valleys and the shores 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 that spewed a ‘lava’ of liquid water. All these features had names, I learned, assigned to them by Earth astronomers centuries dead, who had pored over the first robot-returned images of this landscape. But as nobody had ever come here those names, borrowed from vanished paradises and dead gods, had never come alive.

  I listened absently as Poole and the others talked through their science programme. The atmosphere was mostly nitrogen, just as on Earth, but it contained five per cent methane, and that methane was the key to Titan’s wonders, and mysteries. Even aside from its puzzling central role in the greenhouse effects which stabilised the atmosphere, methane was also central 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 that 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. However, both Berg and Dzik had had specialist training to a decent academic standard to prepare for this mission. Ambitious types like these expected to live a long time; periodically they would re-educate themselves and adopt entirely different professions. I have never had any such ambition. I had a good education that had bequeathed me a good vocabulary and got me selected for my sinecure as a curator, along with my father’s influence – but that was about as much use as it had been to me. Why waste time going through it all again? Besides, 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 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. If we couldn’t protect the ecology, “we’ll implode the damn wormhole. We’ll get funds for the Cauchy some other way.” That’s what you said.’

  Poole said harshly, clearly needled, ‘That was thirteen years ago, damn 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 coal-black liquid surrounded by fractal landscapes, like a false-colour 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 those 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, distracted, absorbed by their science. 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 with a wingspan of ten, fifteen metres. I thought I could hear them, a rustling, snapping sound carried to me through Titan’s thick air.

  And they tore into the envelope. The fabric was designed to withstand Titan’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 crashed into the gondola itself, crumpled like tissue paper, and fell, wadded up, far below us.

  And we fell too, following our victim–assassin to the ground. Our descent from the best part of eight kilometres high took long minutes; we soon reached terminal velocity in Titan’s thick air and weak gravity. We had time to strap ourselves in, and Poole and his team worked frantic
ally to secure the gondola’s systems. In the last moment Poole flooded the gondola with a foam that filled the internal space and held us rigid in our seats, like dolls in packaging, sightless and unable to move.

  Even so I felt the slam as we hit the ground.

  7

  The foam drained away, leaving the four of us sitting in a row. We had landed on Titan the way we had 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 mass of Bill Dzik was weighing on me. The gondola’s hull had reverted to opacity so that we lay in a close-packed pearly shell, 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. I was breathing, the air wasn’t foul, and I was in no worse 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 experienced by the 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.