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.