Poseidon's Wake

by Alastair Reynolds

  ‘Is that safe for you?’

  ‘The ship’s not really built for it. But of course Eunice says safety margins are meant to be tested.’

  ‘Please, Goma – don’t take any risks on our behalf.’

  ‘You don’t get a say, Kanu. Besides, you have one of the Risen with you.’

  ‘That’s true.’

  ‘Around here, at least, the Risen just became an endangered species again. We owe it to ourselves to do all we can for Hector, but I can’t promise it’ll be easy. Our tether’s shorter than we’d like. If we touch down at forty kilometres, we can just reach you, but you’ll need to hold out until you’re close to the limits of survivability. If all goes well, we should be able to get down to you before you’re much higher than fifteen or twenty kilometres up.’

  ‘That’ll be cutting it fine.’

  ‘No other way, Kanu. But we’ll have oxygen and power when we reach you. Don’t be alarmed if you see the ship lift off – Gandhari’s going to circle around for a few hours before coming back in.’

  ‘This is more than we were hoping for, Goma.’

  ‘It’s what Mposi would have done. While we carry his name, we’d better try to live up to it.’

  ‘You already have.’

  ‘I’m signing off now. Once we’re on the tether, we’ll speak again. For now, keep warm and conserve your supplies. See you soon, Uncle Kanu.’

  ‘See you soon, niece of mine.’

  They lowered into the atmosphere on a spike of Chibesa thrust, dialled back to the minimum necessary to support Mposi against Poseidon’s gravity. It was silent to begin with, the descent as smooth and uncomplicated as when they landed on Orison. But the air was thickening with each kilometre closer to the sea, and as the Chibesa exhaust began to interact with the atmosphere, so the physics of the plasma exhaust began to turn messy. The engine could adjust, up to a point. It damped shock waves and smothered runaway instabilities before they had a chance to manifest as bumps or lurches felt by the human crew. It whispered sweet nothings at turbulence and laminar-flow boundaries. It brought to bear a monstrous amount of computation, calculating its way around the curdled, fractal corners of emergent chaos.

  But they had to go deeper.

  Vasin was at the controls, her seat pushed out into the armoured eye of the bubble cockpit, shaking her head all the while as if – despite having agreed to this – she was still not convinced that it was anything but the utmost foolishness, guaranteed to wreck them all. Mposi sounded a mounting chorus of status warnings and master caution alarms, and the engine surged and ebbed as it tried to balance the demands being placed upon it.

  Deeper still.

  Chaotic interaction with the high atmosphere was only part of the problem. Now the heat transfer from the exhaust to the surrounding air was beginning to overload the engine’s own cooling capabilities. Refrigeration pumps and heat exchangers surged and screamed beyond their normal tolerances.

  Still more alarms.

  But Vasin had given Eunice her word, and Kanu in turn had been led to believe there was a chance of rescue. Goma understood, in a flash of admiration and empathy, that Vasin would not now turn back; her commitment was total. Having said she would do this one thing, their captain would not surrender.

  Fifty kilometres from the seas of Poseidon.

  Forty-five.

  Vasin deployed the undercarriage. They had descended on one side of the wheel, but now she vectored them sideways until they were almost hovering over the tread itself. What had been taxing now became doubly difficult because she did not want the Chibesa exhaust coming anywhere near the fabric of the wheel, for fear that it would cause an explosion or be interpreted as a hostile act.

  These fears struck Goma as perfectly reasonable.

  The thrust had to be feathered now, vectored out at sharp angles, and that in turn meant an increased load on the engine just to hover. Mposi by then had gone berserk with its own anxieties. Vasin cancelled all the alarms and got a small round of applause from her crew.

  ‘Probably for the best. I don’t think I want a second’s warning when things go completely wrong.’

  ‘You’re doing wonderfully, Gandhari,’ Goma said.

  ‘You sound like your uncle.’

  Goma did not know what to say to that. But she was not displeased by it.

  Now came the hard part, as if it had been plain sailing until now. They had to land, or at least hold station, while the rescue party was unloaded.

  It would have been easy enough on the wheel’s summit, where the great curve approximated a level surface. Here, though, they were not even halfway to the top. At forty kilometres above the sea, the inclined tread of the wheel was thirty degrees away from a sheer surface. Only the grooves offered any possibility of a secure footing.

  Vasin brought them in close, veered out, came in closer again – all the while making tiny adjustments to the landing gear. ‘No one move around much,’ she said. ‘And if you want to try not breathing for a bit, that would help.’

  The moment of landing, when it came, was barely a kiss of contact. Mposi swayed, its gear taking up the load as the engine slowly throttled down to zero thrust. Through one set of windows, Goma saw only the near face of the wheel, almost close enough to touch if the window’s glass had not been in her way. She wondered how they had managed to land at all.

  ‘Unload as quickly as you can,’ Vasin said, not stirring from her command seat. ‘Use the secondary lock, not the primary, and take care on your way out. Watch when you bring out the winch gear – it’s heavy, and our balance may shift.’

  They had begun putting on their spacesuits before the final approach to the wheel, so now there were only final preparations to be made. Eunice had left her suit behind on Travertine, so they were all using the same standard model carried aboard Mposi. She was less than happy about that, scowling at the life-support controls built into her sleeve and shaking her head in disgust.

  ‘What is this horse piss? You’re supposed to get better at making things, not worse.’

  ‘Shut up and put up with it, the way we have to put up with you,’ Ru said.

  They locked on their helmets, checked comms and began unloading the equipment.

  It was only when Goma was outside that she could see how skilfully Vasin had put down the lander. It had been a tricky bit of work, worthy of grudging admiration even from Eunice. Two of the four landing legs were planted into the groove, compressed to their minimum extension. The other two, stretched out as far as they would go, were braced against the steep side of the wheel between the groove they were in and the next one down. The landing feet on that side were angled to their limit, relying on friction to support them to the lander.

  It looked precarious, which it was. Eunice said that she had seen some nastier landing configurations, but not since the days of chemical rockets. Vasin was even applying a constant torque of steering thrust from one of the lander’s auxillary motors, a cruciform-shaped module high up the side of the hull, near the out-jutting control bubble. Without that corrective thrust, there would be little to stop the lander toppling away from the vertical.

  ‘But I can’t keep bleeding that jet,’ Vasin said. ‘It’s not meant for sustained use, and it’s not fed from the Chibesa core. Once that tank’s empty, we’re in trouble. I’ll need to lift as soon as you’re independent.’

  It took thirty minutes to get all the emergency supplies unloaded and organised – during which time Kanu’s party rose another five hundred metres. Goma was supremely conscious that each second counted against Kanu. Equally distressing was the fear that they would make some miscalculation or omission now, and really damn their hopes.

  The immediate task was to set up the tether and the grapple. The grapple was a thousand kilograms of heavy-duty engineering designed to bear the load of a spacecraft under adverse thrust. It woul
d certainly not fail on them, which was one consolation, but it took two of them to move it, and even in its retracted configuration it only just squeezed through the secondary lock. It looked like a mechanical starfish, two metres across with five independent arms, each of which ended in a complex multifunctional gripping appendage. They wedged the grapple into the back of the groove, cleared to a safe distance, then ordered it to lock itself into place. The arms pushed out with explosive speed, the tips adapting to the sensed surface to provide the maximum locking force. Since the inner walls of the groove were smooth, there was nothing for the grapple to hook on to. But it was also designed to couple with the smooth hulls of other spacecraft, using high-friction pads. Its appendages angled to bring their pads into optimum contact. They slipped a little initially, then held. The three humans approached the grapple again and hooked on the tether. Using the power winch, they tested the grapple up to five thousand and sixty newtons of instantaneous force, at which point it slipped and then regripped. Five tonnes – not much.

  They would never strain it that severely, though, because the tether was going to run over the lip of the groove, which would function as a bearing surface. From Mposi’s repair inventory they found a piece of spare hull cladding which had approximately the right profile to slip under the tether at that point of contact. They fixed it into place with vacuum epoxy, trusting that the bond would hold against the alien material of the wheel, and that the tether would not cut through it.

  They buckled what they could onto the utility belts of their suits, but the emergency oxygen and power supplies were too bulky for that. These items were packed into a zip-up bag which they would lower down ahead of them, strung out like a plumb-bob on a few metres of standard safety line. They used the same line to tie themselves together, again with a safety margin of a few metres.

  Eunice would lead, Goma second, Ru third. Ru was the only one coupled to the tether itself and she had direct control of the power winch, which was connected to the front of her belt by a sturdy clasp. The winch did not look like much to Goma, just a squat yellow cylinder with some hazard stripes and a few simple operating controls chunky enough to be worked with spacesuit gloves. It was hard to believe that most of the fifty kilometres of the tether were still spooled up in the winch’s casing. But then the tether itself was almost invisibly fine, and Vasin had warned them that it could easily slice open their suits if they touched it under tension.

  Or worse.

  Still, doing it this way rather than spooling out from the grapple at least meant there was no moving contact between the tether and the corner piece. Eunice would be their lookout as they approached and traversed each successive groove on their way down. And to stand a chance of helping the others, they would need to be moving quickly.

  Eunice was the first over the lip, with the supply bag dangling under her. She braced her legs against the nearly sheer side and signalled for Goma to join her. Ru spooled out the line, no more than tens of centimetres at a time, until all three of them were over the lip and their weight was borne by the tether. It was easy for Goma – she was coupled to Ru by a stretch of line obviously thick enough to bear her weight. But Ru was barely able to see the tether.

  ‘I’m near the top of the next groove down,’ Eunice said. ‘Start lowering us. I’ll kick off and rejoin the surface under the groove. You’ll have to do the same. Once we get into a rhythm, we should be able to make good speed.’

  It took them a while to get the rhythm of it. They were strung out far enough that Eunice and Ru were both passing grooves while Goma was descending the flat section between them. If they did not time their kicks correctly, there was a risk of Goma being torn from the wall just in time to swing back into the mouth of a groove. At low speeds, little harm could come to her. But to be of use to Kanu’s party, they would need to reach them in under ten hours, and that meant an average descent speed of five kilometres an hour. That was fine in spurts, not even a brisk stroll, but they could not allow themselves to fall behind. Every error counted, and if they had to go faster to make up time, any resulting accident could have serious consequences.

  Thirty or forty minutes into the descent, though, they settled into a pattern. The tether was reeling out smoothly, the grapple holding. Goma stopped concentrating and just allowed her muscles to find the right pace, trusting in the women above and below her. The grooves passed one after another, punctuated by the icily smooth and pristine material between then. The angle of the tread was steepening towards vertical with every metre they descended, but it would be a long while before that became obvious to Goma’s senses. The wheel’s rotation brought Kanu’s party higher with each second, but that same rotation was also working to push Goma’s team higher as well. They could not afford to stop until they had closed the gap to Kanu, and to do so in a useful time they needed to outpace the wheel’s counter-rotation.

  ‘Kanu? This is Goma. We’re descending. How are you coping? Looks pretty dark down there.’

  She had to wait a little longer for his reply than she cared to, as if she had pulled Kanu from the edge of sleep. ‘Dark, but we’re looking forward to company. Swift says we’re at six kilometres now. I won’t pretend it isn’t cold, but the suits are holding out, and there appears to be some heat radiating from the walls of the groove – it’s definitely not cooling down as quickly as the surrounding air.’

  ‘Stay with us, Kanu.’

  ‘I have no plans not to. Having come this far, I’d very much like to finish the job properly and return with a full expedition – human, Risen, machine – whatever it takes. Did you know there are monsters in that ocean?’

  ‘Nothing would surprise me,’ Goma said.

  ‘I say monsters – one of them ate our ship, which didn’t strike me as very gracious behaviour – but I suppose we should reserve judgement. For all I know, that was the M-builders making contact.’

  ‘I think they’re long gone, Kanu.’

  ‘So do I, but it’s a nice thought that we might meet them, isn’t it? At the very least, I’d enjoy telling them they were mistaken.’

  ‘About what?’

  ‘The futility of existence. Ask Eunice – she’s been through the Terror.’

  She told him to sign off until they were nearer, wanting him to conserve energy and oxygen.

  They carried on down, the grooves passing like the stepped-out balconies of an endless hotel. They were only seeing a part of each groove from their line of descent – each one extended to either side for hundreds of metres – but that was still enough for Goma to convince herself that each groove was unique in its detailed form, not just a horizontal slot but a wavering, wandering trench with right angles and zigzags, branches and interruptions. Statements in a language her mother had expected her to be able to read by now, but of which she was still ignorant.

  ‘Look,’ Ru said.

  They slowed instinctively. Above them, a bright flame was rising beyond the convex surface of the tread, cut across by a converging density of grooves like the absorption lines in an atomic spectrum. Captain Vasin had waited until they were this far down before detaching the ship.

  ‘Think she’ll come back for us?’ Eunice asked. ‘The way her hands were shaking on that descent, I thought she was having some sort of brainstem seizure.’

  ‘Give her some credit.’ Goma said. ‘She put that ship down under impossible conditions. Admit it – even you were impressed by that landing.’

  They carried on down a groove or three.

  ‘I’ve seen worse.’

  ‘Such generous praise,’ Ru muttered.

  It had been like that since they left the first groove – Goma caught between the two of them, Ru still needling, Eunice not exactly going out of her way to ease things. It bothered her not to be liked by Ru, Goma decided, but only because Ru was special to Goma. Had Ru been anyone else on the expedition, Eunice would not have cared less. She had
spent her whole life being entirely unconcerned about the opinions of others; she was not about to change overnight, even in this latest and strangest incarnation of herself.

  Goma liked it when they had something else to talk about, and when Ru just got on with working the power winch.

  ‘I wouldn’t say I’m starting to see the bigger picture just yet,’ Eunice said, ‘but maybe the tiniest corner of it. This is almost a different syntax again, you know? It’s like all the work I had to do to make sense of the Mandala script needs to be thrown out and done over.’

  ‘How can you read anything when we’re only seeing a tiny part of each groove?’ Goma asked. ‘Isn’t it like running your finger down the page of a book and only reading one word from each line?’

  ‘No, it’s worse – because this is more like one word from a page, not one word per line. But before we landed I had Gandhari transmit Mposi’s scans into my suit. Granted, it’s only the top of the wheel – a tiny fraction of its total content – but I’m starting to understand.’

  ‘What did Kanu mean – about the futility of existence?’ Goma asked.

  ‘You remember we spoke about the vacuum fluctuations?’

  ‘Barely.’

  But those easy conversations on Orison – before the deaths of the Tantors, before the second Mandala event, before this – felt as if they had happened to a younger, more naive version of herself. It was like reaching back into her childhood.

  Eunice’s kitchen. Mealworms. The joy of knowing Sadalmelik and Achernar.

  ‘The M-builders were too clever for their own good,’ Eunice said. ‘They dug too far into physics and it bit them. Physics will do that. It’s an ungrateful piece of shit. It’s a fickle lover that will always betray you. It courts you, gives you rewards, coughs up little treats like fire and the wheel, telescopes and the secret of starflight, makes you think you’re worth it, that you’re the special one, that you really, really matter to it.’ She paused as she kicked off from the wall, swung out and thumped back into contact. ‘All the while it’s saving up this nasty little truth: that every thought, every deed, every hope you’ve ever held is futile. That the universe will end, and forget itself. That there is no such thing as meaning. That you might as well kill yourself now, because in the end your existence won’t count for anything. That there is no posterity. There is no Remembering. That nothing passes into anything – even for Tantors.’