Xeelee: Vengeance

by Stephen Baxter

  For all the bluffing they were both relieved, Poole thought, when the preliminaries were done, and the moment of launch arrived.

  Mitch Gibson crawled into the pod to shake their gloved hands.

  But their very last human contact – before the pod was sealed and the air replaced with a clear suspension fluid – was with the two young techs who had taken them through the medical stages. Again their hands were shaken.

  ‘The naming of names,’ said the male tech.

  Poole asked, ‘Names?’

  ‘We need call signs. Commander Gibson suggests Anaxagoras for the control station at Larunda. And Cecilia Payne for your descent module.’

  ‘Anaxagoras,’ said the female tech. ‘A pre-Socratic philosopher who was the first to speculate that the Sun might have a physical nature, as opposed to divine. He imagined the Sun was a ball of hot iron mere thousands of kilometres above the Earth.’ She laughed. ‘He was misled by a lack of understanding of the curvature of the Earth. Still, not a bad guess. And Cecilia Payne was a late-Discovery-era solar physicist who made rather better guesses.’

  Poole nodded brusquely. ‘Good names. Anaxagoras and Payne it is.’

  ‘I hope you will remember us. We have worked so closely together. Physical contact brings a bond, does it not?’ She shook Poole’s hand. ‘My name is Asher Fennell.’

  ‘And mine,’ said the other, ‘is Harris Kemp.’

  ‘We will remember,’ Nicola said, gravely enough.

  Poole suspected they were both relieved when the cabin was finally sealed, and the suspension fluid cautiously pumped in. ‘Nicola, I appreciate you not laughing at them.’

  ‘It took an effort, believe me. Those earnest kids.’

  ‘Who will never forget this moment, whether we live or die.’

  Nicola just shrugged.

  Now Gibson called. ‘Anaxagoras here. Larunda control. Payne, Anaxagoras—’

  ‘Anaxagoras, Payne. We have you loud and clear,’ Poole replied. Even if that wasn’t quite true; the suspension fluids had left his hearing slightly muffled, his vision blue-tinged.

  ‘Then if you’re ready for the final pre-launch preparations—’

  Nicola snapped, ‘Enough chatter already. So long, Mitch.’ Her finger stabbed down on a glowing slate.

  And the Cecilia Payne, dragging an electric-blue wormhole frame, lurched into free space. Within minutes they had fallen out of the shadow of Mercury, and faced the raw Sun.

  17

  First they had to travel from Mercury’s orbit to the surface of the Sun: not an inconsiderable distance in itself, nearly sixty million kilometres, forty per cent of Earth’s distance from the star. And, given the stress on their systems, human and mechanical, the sooner that distance was spanned the better.

  So, following the prepared flight plan, Nicola ramped up the GUTdrive to an acceleration of twenty gravities – less than they would suffer at the Sun itself, but a good test of the interlocking systems that should shelter them from that ferocious pull. At that rate it would be five hours to turnaround, then an equally ferocious five hours of deceleration, before they hit the edge of the Sun’s outer atmosphere . . . The edge, at least, as the Larunda crew defined it for practical purposes. Poole knew that to the physicists the star’s extended atmosphere reached theoretically to interstellar space, where the solar wind brushed against the wider galactic breezes.

  Once the thrust was engaged and she was satisfied the craft was performing as expected, Nicola turned to Poole – moving very cautiously – and winked at him through her faceplate and a blue wash of suspension fluid. ‘Wake me if there’s an alarm.’ She closed her eyes.

  After a few minutes her breathing was deep and regular.

  Mitch Gibson spoke in Poole’s ear. ‘Payne, Anaxagoras. How’s it going, buddy?’

  ‘I’m glad of the company. That woman could sleep through the end of the world.’ Although, he thought, maybe that wasn’t something he should joke about just now.

  ‘We rate you at just shy of twenty G. Any problems?’

  ‘Not that I can detect. Breathing is no more uncomfortable than before. Vision seems normal. As the acceleration ramped up I had a few pressure points.’

  ‘We saw them. Your neck, the bottom of your spine—’

  ‘The smart systems compensated before I could report.’

  ‘Unless you want anything, I’ll shut up. Follow your pilot’s example and try to sleep. You’ll face a long day when you wake up.’

  ‘I don’t suppose you stowed away any single malt on this tub.’

  Gibson laughed. ‘Sure. The state you’re in you’d have to inject it straight into your brain pan. Sleep tight, my friend.’

  Perhaps he did sleep. So strange, so unreal was the situation, this cocooning in a technological womb while the Sun’s disc slowly grew before him, it was difficult to know if he was asleep or awake.

  In the end it took the soft chime of an alarm to alert him that the descent phase was over. That was shortly before the GUTdrive faded, and the acceleration softened to zero.

  Nicola woke, stirred, went to rub her eyes, and found her gloved fists thumping against her faceplate. She looked at her hands, listened to the whirr of the exoskeletal multipliers that enabled her to close her fingers, and laughed at herself. ‘Are we there yet?’

  ‘I guess so—’

  ‘I can tell the drive shut down, evidently on cue.’ She checked a monitor. ‘And it left us with the right residual velocity. We’re free-falling, more or less, at the best part of four hundred thousand kilometres an hour . . .’

  The drive had cut out with the craft still about two solar radii above the photosphere, the visible surface: about one and a half million kilometres high. But already they were descending through a hugely energetic environment. This was the corona, the Sun’s outer atmosphere, a realm of super-hot, super-thin gases. And this was the fastest they would travel, Poole knew, until – and if – they emerged safely from the heart of the Sun.

  ‘Four hours to the photosphere.’

  Poole glanced at her. ‘You haven’t looked outside once since you woke up, have you?’ He tapped a button.

  The craft’s hull turned Virtual-transparent. It was as if the two of them, in their couches, with instrument and control banks before them, were suspended in light, with, just behind them, the spectacular frame of the wormhole portal they’d dragged all this way.

  And, dead ahead now, walling off half the universe, was the Sun. A disc that spanned the sky. As seen in hydrogen light it was coloured a vivid orange-brown that crawled with detail. This was the photosphere, the Sun’s visible surface. The texture was grainy, almost as if pixelated – or, Poole thought more brutally, it was like some vast wound infested by a billion squirming insects. But each of those ‘grains’ was typically the size of Great Britain, or larger. Here and there he saw sunspots, huge dark scars; those close to the horizon were foreshortened, and seemed depressed below the general horizon, like craters.

  This lightscape was not tranquil, but turbulent: lashed by huge energies. He saw spicules, fountains of wispy, glowing gas, bursting out of the granulated surface, as well as still more elaborate features: prominences, great glowing arches. These were much more easily seen out towards the horizon of the Sun than head on. The prominences were manifestations of the Sun’s powerful magnetic field, generated deep in its interior – at a zone into which, Poole realised queasily, if all went well, he was scheduled to descend in this frail craft. It was a disturbing thought that such immense limbs of energy might be reaching out towards him even now, all but invisible as seen from dead ahead.

  Mitch Gibson’s voice, calm, reassuring, whispered in his ear. ‘Payne, Anaxagoras.’

  ‘We’re here, Mitch.’

  ‘Hope you’re enjoying the light show. You’ll be aware that we checked the solar weather predictions
before we set the date for your mission. We didn’t want to lower you down in the middle of a storm.’

  Nicola laughed. ‘This is calm?’

  ‘Comparatively. Take a look up to, umm, your top right.’

  Poole had to lean forward to see, muscle multipliers whirring. There, beyond the edge of the Sun, Poole saw a kind of effigy against the black sky, apparently a rough circle, distorted, glowing. He had no way of judging its size. ‘Got it.’

  ‘That’s a coronal mass ejection, or the relic of one . . .’

  The Sun’s magnetic field, distorted by differential rotations in the star’s layers, could become entangled. And, erupting through the surface, every so often these tangles could, in the physicists’ term, simplify: the fields lost that knotted-up complexity all at once, and in the process dumped a load of energy. Tremendous explosions pushed gouts of matter from the surface, amid a hail of high-energy radiation. And in a ‘coronal mass ejection’ a great knot of the magnetic field itself could be expelled, carrying a mountain’s mass of plasma with it, hurled out at a million kilometres per hour. That was what Poole was watching now. Earth’s fragile but recovering technological civilisation had been hardened against such storms for centuries, but solar weather remained a hazard for all of spacegoing mankind.

  But not today, Poole murmured. Not today. They were descending, as Mitch had observed, into comparative calm.

  Their sphere steadily falling, dragging the electric-blue portal with it – Poole imagined the invisible tunnel of the wormhole stretching behind them – it took the full four hours for them to pass through the corona, and a denser, brighter layer called the chromosphere that was only as thick as the Earth’s diameter – a mere detail in this huge landscape – and finally to approach the photosphere itself.

  The surface of light.

  Mitch Gibson took them through final checks before entry. ‘Payne, Anaxagoras. How’s the neutrino scanner?’

  Nicola checked it over. ‘Nominal . . .’

  Poole turned his head, cautiously but with interest, to see the relevant display: a first close-up scan of the interior of the Sun.

  He knew that as hydrogen fused to helium in the Sun’s core, a flood of gamma ray photons was released, packets of energy that had to batter their way through the Sun’s inner layers, absorbed and re-emitted over and over, and out to the surface. Such was the density in that crowded deep that this process was a stop-start random walk, and it could take hundreds of thousands of years for the energy carried from the core by a single photon to reach the surface, and then sail unimpeded through space, to illuminate a target like planet Earth. To neutrinos, though, another product of the fusion processes – ghostly particles to which even the densest matter was far more transparent than air was to sunlight on Earth – the journey out of the Sun took mere seconds after their creation in the core. And so the neutrinos offered a way to look within.

  Once, as Poole, a fan of archaic technology, had learned, to detect even a fraction of these neutrinos had taken huge, ungainly, mass-heavy ‘telescopes’: vast tanks of fluid stuck down mine shafts on Earth, for instance. Now the neutrino scanners whose results Nicola consulted were smaller than Poole’s fist.

  And the data they delivered was interpreted in the consoles as a ghostly image, as if the Sun was rendered transparent as glass, save for a star-like object contained in its very heart – the core itself, a fusion engine larger than Jupiter. Away from the core only the faintest of details could be seen, for now. But Poole knew that it was hoped that as the descent progressed this suite of instruments would be sufficient for them to detect the Sun’s recent visitors.

  ‘OK,’ Nicola called. ‘Coming up on the photosphere. Hold on to your lunch . . .’

  Under Nicola’s command, the angle of their fall abruptly flattened out. Poole felt a deep, savage surge of deceleration, and the Sun tilted, turning from a wall of light ahead into a kind of landscape beneath him. As he sat in his couch a tremendous weight dragged on his bones; he found it suddenly an effort to take a breath. But the manoeuvre was over, and now the craft settled into a low, rapid glide over the solar surface. With the hull still set to Virtual transparent, Poole could see how he and Nicola were underlit by a complex carpet of light.

  He dared not turn his head. But a monitor showed him Nicola’s grinning face – a lopsided grin, distorted by the gravity. She said, ‘Welcome to the Sun.’

  ‘Payne, Anaxagoras,’ Mitch called. ‘We’ve got good telemetry. The ship’s systems, your own medical signatures, everything shows nominal.’

  ‘How reassuring,’ Nicola said.

  ‘And enjoy the view. We’re getting great imagery up here.’

  Now it was as if they flew over some immense cauldron, its surface dominated by huge, slow-swelling bubbles, hundreds of kilometres across, each traversed in minutes. These ‘granules’, some of them organised into vaster clusters, were the termite-like infestation Poole had seen from afar. Close to the surface they seemed less lifelike, more mechanical. That analogy of a cauldron was apt; what he was seeing were the upper reaches of huge convective fountains that stretched deep into the Sun’s interior. Further ahead he could see sunspots, distinctly foreshortened now, with wisps and arches of glowing gas reaching up into space. The sunspots were scars that showed where the Sun’s magnetic field disrupted the deep convection flows, creating cooler patches.

  ‘Payne, Anaxagoras. OK, guys, you’re coming up on your first target. Should be over your horizon in five, four—’

  ‘Mitch,’ Nicola said, cutting him off. ‘I already see it . . .’

  And, looking ahead, so did Poole. A huge form pushing out of the glowing photosphere. Like a wall, smooth-faced, sharp-edged, pale.

  A building, on the Sun.

  ‘The Cache,’ he breathed.

  ‘That’s the one,’ Mitch Gibson reported. ‘Glad we could bring you down close enough for a visual. You may see that it’s half-immersed in the photosphere – as if floating there. But neutrino and other scans show it has the same proportions as when it emerged from Mercury. A precise cube.’

  ‘Same proportions, maybe,’ Nicola murmured. ‘But look how far away we are from the Lethe-spawned thing, Poole. How big was the Caloris impactor? A hundred kilometres across? Whereas that—’

  ‘Payne, it’s now more like a thousand kilometres across. I did say it started growing as soon as it came out of Caloris.’

  Nicola somehow laughed. ‘Yes, but you didn’t say this much. It’s like the box Ceres came in.’

  ‘Mitch, is it still growing?’

  ‘No – well, not that we can see. Michael, we think that the material of which that big hull is made is some kind of light-energy receptor. A perfect solar cell. And it turns the energy it captures, with perfect efficiency, to mass. The bigger it gets, obviously, the more light it can intercept, and the faster it can grow—’

  ‘Exponential growth,’ Nicola said.

  ‘That’s the idea. Of course the rate at which it grows depends on the input energy flux. It was already growing, we think, as it approached the Sun, behind the sycamore seed; now it’s bathing in light. Our observations of the early stages are patchy. But we think it had a doubling time, in terms of surface area, of a couple of hours.’

  Nicola thought that through with characteristic quickness. ‘OK. So it grew to its current size in, what, twelve, fifteen hours?’

  ‘Something like that. Then it stopped.’

  ‘Do we know why?’

  ‘Internal complexity,’ Poole guessed. ‘First it inflated the shell to the required size. Now it’s growing inside, not out. Some kind of infrastructure filling it out.’

  ‘And the result will be what?’

  Poole shrugged. ‘Whatever those who planted it in Mercury, five billion years ago, intended for it.’

  ‘We’ve no way of telling,’ Gibson said. ‘The sycamore se
ed seemed to monitor it for a while, having, apparently, guided it here from Mercury. Then, as you know, the seed just dived into the Sun. We do have partial observations that indicate that some of the objects you called raindrops – the silvery spheroids – may have entered the Cache, once it was settled. But that’s disputed. As for now, not even neutrino scans can penetrate that material. Which is why, incidentally, we hope that the sycamore seed will show up in your own scans, at least as a shadow against the core-neutrino glow. We are sending probes past the Cache, and seeing how they’re deflected by its gravity. Hoping to pick out some internal detail that way.’

  Poole looked at the shining box. ‘I’m itching to look inside that thing. Find out what in Lethe they’re doing in there.’

  ‘That’s for the future,’ Nicola said firmly. ‘We have a job to do. Let’s get on with it.’

  Poole didn’t see her move a muscle.

  But the Payne tipped up and plunged straight into the surface of the Sun.

  18

  The so-called convection zone – the outer layer of the Sun’s deep, stratified structure – was indeed a cauldron, a great spherical pot of boiling material wrapped around the Sun. A cauldron more than a hundred thousand kilometres deep.

  Poole knew he was falling into a tremendous heat engine, whose principles would have been recognised by Discovery-era thinkers – indeed the basic physics of the Sun, and of all stars, had been worked out in that age of engines of steam and internal combustion. The Sun’s material here was a gas, ionised, but not so hot that atomic structures broke down. So, just like Earth’s air, it was a gas that was capable of absorbing and retransmitting the heat energy of the photons singing up from the Sun’s core. And this gas boiled, exactly like a pan of water heated from below, with the heat energy transported by convection: the rising of hotter fluid, the falling of cooler.