Poseidon's Wake

by Alastair Reynolds

  But perhaps she knew he was lying. ‘Good,’ she answered, with a coolness of tone that said she had seen right through him. ‘Let’s try and keep it that way, shall we?’

  Kanu nodded. It was a small thing, but he would take what he could.

  Days and weeks brought them nearer to Poseidon. The improvement in knowledge was steady rather than dramatic, their view of the system gradually sharpening and gaining detail and texture. After the initial discovery of the second Mandala and the arches there were no great surprises, just reinforcement of what they already knew. The Mandala was definitely real; the arches were definitely not of natural origin.

  Beyond that there were hints of further interest, but nothing that answered Kanu’s central question: who or what had need of Ndege Akinya?

  Paladin had a very small moon. That was not unusual in itself, but this misshapen little body was odd in a number of ways. It was too warm, for a start: much hotter than would be expected given the standard thermal equilibrium for something in its orbit and distance from Gliese 163. Kanu wondered whether the rock might have been an asteroid, or the remains of one, captured after some violent collisional process. Such an encounter would have needed to be recent enough that the thermal energy of the event was still bleeding away into space.

  It became even stranger, though, because in addition to the overall temperature of the rock, there were a handful of even hotter regions on its surface. They were like the infrared traces of fingerprints left on an apple held in a human hand. They were hot enough – up in the three thousand kelvins – that they made him think of geysers or volcanic outflow points. Strangely, though, there was no trace of material boiling away into space.

  What was making those hot spots glow? Were they natural features or evidence of deliberate activity? He had been aiming transmissions at the rock but nothing had come back from it. Kanu knew he would need to take a closer look, if for no other reason than to satisfy his curiosity about the peculiar heating effect. But that would be no inconvenience since he would want to examine the second Mandala in any case.

  Closer to Poseidon, they found a secondary mystery. The arches were numerous and tantalising and definitely warranted examination. But lacing Poseidon – orbiting at different inclinations, in the manner electrons were once thought to orbit the atomic nucleus – was a host of small dark moons. They buzzed around Poseidon like flies, shell after shell of them. There had been no hint of them in the Ocular data, but that was to be expected. Dark as night and much smaller than the planet, they would have been almost impossible to resolve in time-averaged exposures, even when they passed across Poseidon’s visible face.

  Clearly, they were not natural. Even if the moons were natural in origin – and their uniform size, shape and reflectivity suggested otherwise – they had most certainly not fallen into these orbits by chance.

  The moons’ orbits ranged in diameter. The smallest nearly skimmed Poseidon’s atmosphere, almost down to the tops of the arches, while the widest spanned a distance of ten light-seconds. Between these extremes lay another fifteen shells. There were forty-five of these tiny moon-like objects in total, but no natural moons.

  Kanu’s instinct was to avoid them. But they threshed around Poseidon in perfectly repeatable patterns, tracing staunchly Newtonian paths like marbles in grooves. Clearly their individual masses did not perturb each other, or the effects had been allowed for in some way. He could already calculate their positions to many centuries hence and be confident of his predictions. Threading Icebreaker through the weave of moons was a trivial matter: there were countless viable trajectories. The hard part would be choosing which he preferred; how close he was prepared to get to the world and to any one of its moons.

  There was time to think it over – and of course it would not be a decision he took alone.

  Nissa remained distant, offering no hint of imminent forgiveness. But her anger had softened to the point where they were able to have mostly cordial exchanges, even if there remained an underlying and unresolved tension. They kept themselves to themselves, occupying different bedrooms. Icebreaker was not a large starship, but there was space enough for privacy.

  They did manage to put aside their differences long enough to eat together. They sat opposite each other, in high, stiff elephant-carved dining chairs, in a room set off from the control deck. Sometimes they ate in silence or with some musical accompaniment, often very old recordings. Occasionally the walls displayed moving images of African landscapes at dusk, skies like flame, trees like dark paper cut-outs against that brightness.

  ‘With your permission,’ Kanu said one evening, ‘we’ll take a closer look at Poseidon.’

  ‘Permission?’

  ‘Wrong word. Mutual consent. If you agree it’s the right thing to do.’

  Nissa was silent. Kanu knew better than to press her. He studied her face, her eyes averted from his gaze – as if the act of eating demanded her total concentration. He still loved her. The more she pulled away from him, the more he wanted her. He thought of gravity, of inverse squares and the swarm of moons girdling Poseidon.

  ‘You’d have to be a corpse not to be interested in those arches,’ she said eventually. ‘That doesn’t mean I’m enthusiastic, or that I like this situation.’ She ate on. ‘I just want to know as much as possible, given that my survival may depend on the choices we make.’

  ‘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 wat
er 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.’

  Before the face assumed focus, something cool and sweet and soothing touched her lips. She thought for a drowsy instant that this kind form was Ru, for the voice was a woman’s. But it was Captain Gandhari Vasin helping her back to life.

  ‘Thank you,’ she said, when she was at last able to coax some sounds from her mouth. ‘I wasn’t expecting . . . I mean, you didn’t need to.’

  ‘I didn’t need to, but if a captain can’t welcome her crew back to the world of the living, what can she do? Anyway, I need you, Goma. Take your time – getting up and about is hard enough after a normal skipover interval – but I have something of interest to show you when you’re ready.’

  Her eyes still would not focus properly, but the vague textures and colours of her surroundings were enough to establish that she was still in the skipover vault.

  ‘Are we safe? Did we make the crossing?’

  ‘Yes, we made the crossing. Seventy light-years, and not a single mishap. How much of that we owe to the Watchkeeper ahead of us, I don’t know. But the ship is in good condition, and we are where we wished to be.’

  ‘What have you found?’

  ‘A great deal. Most importantly, though, a wel
come message – a signal telling us where to go. I think you should hear it. I would be very glad of your opinion.’

  ‘How is Ru?’

  ‘There’s no need to worry about Ru. She’s in excellent hands.’

  That was meant well, but it was not quite the answer she had been hoping for. And yet Goma could only focus on her fears for so long before drowsiness pulled her under again.

  She had no idea how long she was out, but there came a moment when the face of Dr Saturnin Nhamedjo was assuming gradual focus before her. He was studying her with magnificent and serene patience, as if nothing in his universe was more valuable than the health of this one patient. She could easily imagine that he had been there for hours, waiting by her skipover casket, untroubled by any concern save her own well-being.

  ‘Welcome back, Goma. I know you have already spoken to Gandhari, but I will reaffirm the news. You have come through safely. All is well. We have all survived skipover – even our prisoner.’

  She thought of Grave, and that in turn made her think of Mposi. But for the moment there was only one thing at the forefront of her concerns. She made to get up out of the casket, forcing effort into unwilling muscles.

  ‘Steady!’ Dr Nhamedjo said, smiling at her determination.

  ‘I want to see Ru.’

  ‘In good time. Ru is receiving the very best care and I am perfectly satisfied with her progress.’

  ‘Something went wrong, didn’t it?’

  ‘We have all survived. This is a blessing. Anything else must be considered a minor setback, nothing more.’ A stern, admonitionary tone entered his voice. ‘I do not wish you to overtax yourself, Goma, not during these early hours. You have more than enough work to do in building your own strength back up. Leave Ru to us. She will be well. I have the utmost confidence in her.’

  ‘Is it the AOTS?’

  ‘It was always going to be a complicating factor. An already damaged nervous system is not best equipped to deal with the additional stresses of skipover, but I would not have agreed to let her join the expedition if I did not think her strong enough.’ He reached into the casket and patted her wrist, offering reassurance. ‘She is in a medically induced coma now, but that is for her own good. We are giving her a cocktail of drugs that will help with the combined effects of AOTS and the ordinary stresses of skipover. There is no reason for them not to work, but it must be done carefully, and the results monitored at each step. Gradually, she will be elevated back to proper consciousness. I have every confidence that she will be well again.’