Poseidon's Wake

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‘I feel similarly.’

She shot him a sceptical look. ‘Do you?’

‘On one level, I’m terrified of that planet. It’s too huge — and those arches? They’re a slap in the face, a boot crushing down on human ambition. But I want to know what they’re for. I want to see them up close.’

Nissa poured herself a glass of wine, steadfastly omitting to charge Kanu’s glass at the same time.

‘There’s a Mandala on that other planet.’

‘Paladin.’

‘And arches on Poseidon. They don’t look alike, but I suppose they both require a technology beyond anything we have. Do you think they were put there by the same culture?’

‘No clue, but I’d like to find out. My guess? There’s a connection. To those moons, too.’

‘And what about the chunk of rock orbiting Paladin that Icebreaker can’t explain?’

‘I don’t know. It doesn’t appear to fit. The other things are recognisably alien — Mandala, the arches, maybe the land masses on Poseidon, the forty-five moons in those weird orbits. This is just a lump of rock that’s slightly too warm. I scanned it with radar, too — some metallic backscatter, but it’s different in composition from the arches’ signature. It could just be mineral deposits baked onto the surface — you’d have to ask a geologist.’

‘But you don’t think so.’

‘I think it’s something else that doesn’t belong, but which is different in nature from the other things. This system is strange enough that we’d have sent an expedition here sooner or later, so why would it not have interested other civilisations? Maybe we’re not the first explorers.’

‘There’s something missing, though. Something that ought to be here but isn’t.’

‘I had the same thought.’

‘Where are the Watchkeepers?’ Nissa asked.

Icebreaker’s planned course took them into the thresh of moons, slipping through their paths halfway between Poseidon and the highest orbit of its satellites. The trajectory would provide an opportunity to look at the moons in closer detail, but Kanu’s chief interest lay in the arches, rising from the ocean like the glimpsed coils of sea serpents.

Slowly their view of the arches improved. Only the tops were free of atmosphere, but much of their height was in extremely tenuous air, offering little obstruction to Icebreaker’s sensors. The arches were semicircular, rising one hundred kilometres from the ocean’s surface — identical in every dimension to the limit of Icebreaker’s measurements. Beneath the water there was a hint of continuation, a suggestion that the arches were in fact only the visible portions of half-submerged wheels, but that was as much detail as they could discern from space.

If they were wheels, then their treads were a kilometre wide, very narrow in comparison to their heights. Their rims were also about a kilometre thick, and there were no spokes or hubs. The arches — wheels, perhaps — were made primarily of some pale grey non-metallic substance, presumably possessing immense structural strength. From deep space, Icebreaker had detected the radar backscatter of metals, but this turned out to be a kind of ornamentation or embellishment added to the surface of the wheels. Cut into the rim and the treads, inlaid or recessed, perhaps even as a bas-relief — it was impossible to tell from space — was a suggestion of dense metallic patterning. To obtain a clearer, more detailed view, they would need to get much closer than five light-seconds. Icebreaker was not meant for atmospheric flight, but it could land on top of one of the wheels, which in turn would give them indirect access to the surface. Other than Fall of Night, there was nothing aboard Icebreaker that could serve as a shuttle, lander or re-entry vehicle — at least nothing with the capability of returning. If their other options were exhausted, there were single-use escape capsules which ought to be able to make it down to Poseidon’s seas.

But not now. This was a first pass, a scouting expedition. When they gained a better look around the system, identified the origin of the signal and found water ice to convert to hydrogen, which would in turn feed the initialising tanks for the PCP drive and guarantee them a trip home — then they could think about taking a closer look at the wheels.

‘We need another word for them,’ Kanu mused. ‘“Wheel” isn’t big enough. Worldwheels, perhaps. Do you like that? The Worldwheels of Poseidon. Has a certain ring to it.’

‘Whatever you think.’

‘I think this is wonderful and terrifying, and I wouldn’t miss it for a heartbeat.’

‘You came here to aid the robots, not to sightsee. Don’t forget the real reason for this trip.’

He smiled, still in the happy rush of discovery. ‘How could I?’

‘And what does Swift make of all this?’

‘Swift is all intellect — brilliant and fast. Swift by name, Swift by nature — but Swift doesn’t actually know very much. There wasn’t room in my head for him to carry a universe’s worth of wisdom — I carry my memories, my life experience. Swift can draw on my knowledge to some extent, sample my memories, but mainly he’s here to serve as witness, to guide my interpretations and actions.’

‘You haven’t answered my question.’

‘Swift wonders if machines made the wheels. The worldwheels. And Swift wonders if that would make them gods.’

‘So your friend has begun to turn to faith? I’d watch him carefully if I were you.’

‘Robots are entitled to ask the same questions as the rest of us,’ Kanu said. ‘There’s no law against it.’

Soon they were inside the orbit of the moons, still moving at a hundred kilometres per second.

The forty-five moons were all alike as Icebreaker could tell: each a perfectly regular grey sphere two hundred kilometres across. They were still very hard to see, swallowing or scattering electromagnetic radiation and offering nothing to Icebreaker’s other sensors. No hint of mass, or magnetism, or particle emission. Artificial, certainly, Kanu decided — and while the moons were larger than the worldwheels and the arrangement of their orbits an impressive feat, he found them less daunting an achievement than the surface structures. They were worthy of admiration, certainly, and definitely merited further attention — but he was content to relegate them to third place after the new Mandala and the worldwheels. They would suffice for study when the other wonders had been picked clean.

But as Icebreaker nosed its way through the dance of orbits, its sensors detected another dark thing circling Poseidon.

It was smaller than any of the moons, and consequently they had missed it until now. It was a light-second or two closer to Poseidon, orbiting more swiftly.

Kanu’s first thought was that they had chanced upon a piece of captured planetary debris — a tiny natural moon, blemishing the order of the forty-five artificial satellites. No solar system was free of primordial material, after all, and sooner or later some of those wandering fragments of early planet formation were bound to become gravitationally ensnared, tugged into orbits around larger worlds.

He was curious, though. Maybe there was water ice on this shard, tucked away in the shadows of craters. Maybe they could use it as a base for operations when they returned to take a closer look at Poseidon. He ordered Icebreaker to concentrate all its sensors on the little fragment and waited as the results appeared before him.

There it was: a sheared-off splinter of some larger thing — wider at one end than the other and hacked across at an angle with a very clean separation. Kanu stared at it wordlessly. He felt himself on the cusp of some vital recognition but not quite able to make the link.

It was Nissa who identified the thing.

‘That’s a Watchkeeper,’ she said, with a cool, calm reverence in her voice, as if she were speaking of the recently dead.

Which was perhaps the case.

It was the corpse of a Watchkeeper, not the living whole. They were looking at perhaps half of its former extent. It had been sliced in two, severed along an impossibly precise diagonal.

Kanu thought of the Watchkeeper they had seen on their way to Europa — the pine-cone form, the stabs of blue radiation spiking out from between the plates of its armour. They had always been dark apart from that blue light, but here there was only darkness.

‘Something killed it,’ he said.

CHAPTER TWENTY-ONE

Goma’s first thought, when the fog of revival had cleared sufficiently for something like consciousness, was that Mposi and Ndege, sister and brother, her mother and her uncle, must by now be united in death. There could be little doubt of this, given the fact of her own survival. There would have been no cause to wake her before journey’s end, no accident that her body would have been capable of surviving, and at the same time, no chance that her mother had survived the long decades of Travertine’s crossing.

They had said goodbye, Goma reminded herself — or at the very least ended things well, with her mother’s loving imprecation that she had to look inside herself now, to find the strength she had depended on in Mposi, and to be that rock for the rest of them.

But Mposi was still dead, and the truth of that was no easier to bear now than before she had gone into skipover.

Presently there was a face, and a voice.

‘Gently now.’