Xeelee: Vengeance

by Stephen Baxter

  Poole was embarrassed. ‘I’m supposed to be the space engineer.’

  ‘This isn’t anything you built, my friend. Or any human. No wonder it awes us. Maybe that engineer’s imagination is more easily dazzled; you understand it better than I do. However, we have got work to do.’ With one booted foot he kicked the tyre of the surface rover. ‘This thing checked out?’

  ‘Ready when you are.’

  ‘You drive.’

  Poole jumped into the left-hand seat and strapped in. He started the engine; he felt a hum, a subtle vibration.

  ‘So, which way, Nicola?’

  ‘You want to make straight for an edge?’

  ‘Seems the simplest plan. Which edge? We’re right at the centre of the face here, so equidistant—’

  ‘The Sun’s to your right, yes? Call that east. So head north. Neither into the Sun, nor away from it.’

  Poole glanced at Grantt, who shrugged. ‘North it is.’

  Poole swept his hand over a softscreen control, and the rover surged forward.

  29

  For the first few minutes Poole gave the rover its head. He tried sharp turns and emergency stops, and ran the vehicle up to its advised limit, of a hundred kilometres an hour. The virtual absence of a downward gravity pull was confusing, but it was a little like driving on a low-gravity world like Earth’s Moon, even Io. The ingenious adhesive wheels worked smoothly, so far as he could tell.

  Just as the GUTship and indeed the flitter were both bright with messages of friendship for any Cache aliens, so, as they drove, was the rover, Grantt told him now.

  Nicola had them stop after five kilometres. Here they adjusted their suits and bucket seats, checked over the rover, and took gravity readings. They even set up a manual plumb line on a three-legged stand. The downward direction of gravity here diverged from the vertical by half a degree: far too slight to notice, but easily measurable.

  Nicola said, ‘There’s the proof that you really are driving around on a big box. The gravity field is complex, but the mass of the box itself is a fraction of that of the central object inside – whatever that is. And even that is extended. Still, to a first approximation gravity points to the centre of the box. And as you move away from the midpoint of a face, the gravity vector tilts away from the local vertical and back to that centre. From here on in it will be as if you are climbing an increasingly steep hill. But you’ll barely notice the effort.’

  Poole packed up the plumb line. ‘So we move on. Next stop a hundred kilometres? If all goes well.’

  ‘Actually,’ Nicola said, ‘take a slight diversion. A couple of degrees to your right. Something interesting for you to pick up on – a probe just spotted it. Don’t worry, Jack; all this has been approved by your bosses in their nice safe domes on Mars.’

  Grantt frowned as he strapped himself in. ‘Another of those dimples?’

  ‘Not that. Something that might have come out of one of those big holes, though . . .’

  Poole and Grantt exchanged a glance. Without a word, Poole accelerated away.

  It took an hour to reach the destination, eighty-eight kilometres from the flitter at the centre point. As they approached Poole saw a scatter of debris, what looked like pulverised rock dust – presumably the relic of the splash of a meteorite against the Cache’s resilient hull plate. But, half-buried under the debris, there was something else. It looked like a scrap of silvered cloth.

  They stopped a cautious distance away. Again they made a manual check of the local vertical: gravity was now ten degrees away from the floor’s perpendicular. When Poole stood, he could feel it now, feel how the ground under his feet seemed to tip up before him.

  Poole and Grantt approached the small debris field together. Cautiously, Poole knelt down, gazing at the skin. It looked like very fine reflective film.

  ‘OK,’ Nicola said. ‘Good imaging. Let me tell you what the various boffins are making of this. Michael, remember the raindrops?’

  ‘The silvered spheres that chased out of the wormhole after the sycamore seed – the Xeelee.’

  ‘Yes. They went to Mercury with the Xeelee. Many of them seemed to have entered the Cache then, before it got to the Sun, and more of them have come and gone from inside there since then.’

  ‘Hmm. Maybe via the dimples, the surface marks.’

  ‘The only indication we have of any kind of entrance, yes. We don’t know if these are the same critters as came from the wormhole or not, or if they are being created in there.’

  ‘Or if they’re breeding,’ Grantt said softly. ‘But then I’m a biologist. I would say that.’

  Poole said, ‘And what we’re looking at now—’

  ‘It seems that one of the raindrops got hit by a stray meteor fragment. Just dumb bad luck, caught as it crossed the surface. Its partners came out to collect the remains. But—’

  ‘But it looks like they left a scrap of skin behind,’ Grantt said. ‘We know something about this stuff too, from remote studies. Same kind of material as the hull plate, same kind of self-growth capabilities in sunlight, same density, but finer. We’ve been calling it membrane.’

  Poole frowned. ‘I heard that hull plate is thinner than a soap bubble. Thinner than that?’

  ‘A lot thinner. Think of a proton’s width.’

  Poole shook his head. ‘I’m an engineer, not a physicist. What force could hold something like that together?’

  Grantt just shrugged. ‘Best guess is it’s something like a Bose-Einstein condensate. That is, matter which displays quantum phenomena on a macro scale. The material equivalent of lased radiation. Although to get such behaviour you generally have to chill stuff down almost to absolute zero. Well, if we take a sample, we might find out.’

  They moved forward together. Cautiously, with their gloved hands, they brushed away the meteor debris. The scrap of membrane exposed was small, no larger than a handkerchief, Poole thought.

  Grantt took this in his hands, in the shade of his body. ‘I don’t feel anything,’ he reported. ‘No suit alarms ringing. I don’t think I’m being harmed in any way.’

  Nicola said, ‘Get it stowed.’

  ‘No. Wait.’ Poole stared at the scrap. ‘If this stuff has the same properties as the hull plate, if it can convert radiant energy into mass – if it grows in sunlight . . . The hull plate growth was pretty spectacular, remember. On the surface of the Sun, it doubled in area every couple of hours. Out here the Sun is more than two hundred million kilometres away. The radiant energy is a lot less. But this stuff is much finer than hull plate. So it might need much less sunlight to make it grow.’

  ‘You’re seriously suggesting I hold this stuff up in the light and see what happens?’

  Poole grinned. ‘We’re here to explore. Try it.’

  Nicola said, ‘Listen, you’ve got my vote. But there’s a yammering of protest in my ear. Michael, stand back – just in case.’

  Poole went to stand on the far side of the rover.

  When Grantt held up the scrap, the membrane grew, visibly, in his gloved hands, expanding, spilling out in the sunlight. It looked to Poole as if he was shaking it out, unfolding a sheet.

  Later they estimated that, in Martian sunlight, a given area of membrane would double in size in just seconds. Light to mass, effortlessly. Poole the engineer thought this was utterly wonderful.

  They packed up the membrane blanket in a light-sealed bag and drove on.

  From then on they barrelled towards the edge in their rover, making a hundred kilometres in each hour, or a little more. Periodically they stopped to check their systems, to make local measurements.

  At two hundred and fifty kilometres out from the flitter the ground felt as if it were tipped up at nearly thirty degrees. Looking ahead wasn’t so bad, but looking back was like staring down a tremendous slope. The flitter, of course, was long since l
ost in the detail; save for the trail of their nanocarbon umbilicals the surface was unmarked.

  There was intense debate now among those overseeing the mission, on the wisdom of going any further. But Grantt was robust. ‘Well, aside from the fact that we have several ways to get off this box, and that our suits will keep us alive for twenty-four hours at least . . . Also, the slope looks worse than it is. Remember the gravity is only one per cent; we can barely feel it. Why, we could just lie on our backs and slide all the way back to the flitter. And finally – Lethe, having come all this way, I want to reach that edge. Michael?’

  Poole grinned.

  Nicola said, ‘I am never going to forgive you for this, Poole.’

  So they drove on. Fleas clambering over that packing-case, a minuscule expedition. Steeper and steeper the slope became, approaching one in one.

  Almost six hours after they left the flitter landing site, they reached the edge.

  They parked up the rover, clambered out, and walked, side by side, the last few metres. There was the edge, visible before them, a dead straight line against the stars. Another step and another, as if climbing a pitched roof.

  And they reached the peak. Poole took one more stride so he comfortably straddled the edge itself, one foot to either side, and the gravity, such as it was, pulled him straight down. It really was like standing on the roof of some vast building, with the twin plains, as featureless as each other, sweeping away to either side.

  He laughed softly, in wonder. ‘Somebody made this.’

  ‘They did indeed,’ Grantt replied. ‘And here we are.’

  ‘O brave pioneers! If your heads swell any more you won’t get your helmets off.’

  Poole grinned. ‘You got news for us, Nicola?’

  ‘Yes. Another fresh observation. But it will mean another detour.’

  ‘An observation of what?’

  ‘Back down the face, about a hundred kilometres past the flitter. Remember those dimples where we guessed the hull might open up?’

  ‘Yes?’

  ‘The hull just opened up.’

  Grantt and Poole stared at each other.

  Poole said, ‘And what’s happening there?’

  ‘Raindrops, coming in and out.’

  Grantt asked, ‘What are our options?’

  ‘Well, you can scoot back to the flitter and run home to Mommy. I’d say that’s the consensus recommendation.’

  ‘Or?’ Poole prompted.

  ‘Or you can go back in the rover, drive down, take a look. Drop in a probe, maybe.’

  Poole hardly dared breathe. ‘Or, better yet, we just fly inside in the flitter.’

  ‘Yes – just checking that out – the lesions are big enough. Although flying the flitter inside the Cache rules out all sorts of abort options. Mission rules and all . . .’

  ‘Jack, what do you think?’

  Grantt took his time to answer. ‘Nicola, you think we could get trapped in there?’

  ‘Well, the dimple took its own sweet time to open. And it’s big. No reason to think it’s going to snap closed. If you don’t stray too far from the hole, I think you’d be safe enough. You’ve got the whole Solar System watching over you, after all.’

  Now Grantt faced Poole. ‘Michael?’

  ‘We came to explore.’

  ‘Yes. And this may be our only chance to get inside there. In fact, our only chance for first contact. As people have dreamed of for centuries. We have to do this.’ Grantt looked around. ‘But I’m going to come back out here another time, and climb a vertex. What a view that would be, the junction of three faces. Like a mountain summit, a thousand kilometres tall.’

  ‘But not today.’

  ‘Not today. Let’s go get that flitter.’

  30

  They had to get to the Cache’s hull breach before it closed again – ideally, Poole thought wryly, they needed to get in and out of the interior before the breach closed.

  So they got back to the flitter as quickly as their rover would let them. Poole, driving aggressively, learned to ignore the pings and stern vocal warnings of the vehicle’s onboard sentience.

  If anything Grantt was even more impatient than Poole himself, and as they skidded down the shallow apparent slope, he cursed the reluctant rover imaginatively. That reaction wasn’t necessarily a good one, Poole realised. Poole had every respect for the Martians and their record for survival on a lethal world, but suspected that Grantt, as he dug his cautious trenches in the Martian dirt in search of traces of his Lattice, had never faced a situation as novel, as full of unknowns as this – and potentially as fast-changing.

  Whereas Michael Poole had built spacetime wormholes in the middle of the Io flux tube, and mined exotic matter from the clouds of Jupiter.

  Nicola fed them updates. ‘Your lesion is staying open, and stable at a hundred metres across. In fact the panels of armchair philosophers who are following your progress are wondering why it needs to be that big; it’s a lot bigger than any raindrop we’ve seen. I’m figuring out ways for us to talk, if you do go inside. The hull plate won’t pass our comms, not even a neutrino beam, but I can position a relay probe over the lesion.

  ‘Oh, by the way, there are a couple more lesions – that’s the emerging consensus term for them – opening up on other faces of the cube. Three in total. Nobody knows how or why; we have drone ships investigating. And why three, not one or six . . . And why now? Maybe you’re just lucky. But it’s as if you’re being invited in, Michael. That spooky Poole charisma’s working again.’

  Poole didn’t respond to that.

  ‘You’re nearly at the flitter. Any last-minute doubts about going inside Pandora’s box?’

  ‘More mythology, Nicola?’

  ‘What’s your choice, heroes?’

  Grantt grinned. ‘What do you think?’

  At the flitter they boarded quickly, leaving their other gear, including the rover, scattered on the surface.

  Within minutes, the flitter was poised over the lesion in the hull plate.

  Poole set the flitter’s hull to Virtual-transparent. Now, suddenly, he could see below his feet the Cache surface, a floor beneath the craft that divided the universe in two. The lesion was a breach right beneath him. A kind of soft pink light shone up through the breach – evidently elsewhere this interior light was blocked by the hull plate.

  And Poole’s sensors showed that the environment in there was warm; the underside of the flitter was bathed in infra-red radiation. The Cache’s internal temperature was maintained at a balmy thirty degrees, like a tropical summer’s day on Earth. Not what Poole had expected, but nothing the ship couldn’t handle. What was odder still was that there was some kind of material in there: gases, a sparse atmosphere – moist, warm air of some kind – air that failed to rush out of the Cache despite the huge breach in the hull. Another mystery among many, Poole thought.

  And, deep inside, Poole glimpsed some kind of mass, locked up within this tremendous box. A glimpse of landscape, almost, folded over, all the colours wrong . . .

  Poole blipped his thrusters. The descent began.

  The ship dropped easily down through that hole in the hull.

  Poole saw the breached surface rising all around him, a layer evidently blade-thin – the thickness of a soap bubble, as he remembered the analogy. It was like a gentle elevator descent through the roof of some huge Martian arcology, perhaps. And the passage was smooth, without turbulence or juddering. If there was some kind of force field holding in the interior air, it didn’t impede the flitter as it passed.

  Soon, so the sensors informed them, they were bathed in warm, moist gas. And below, that big mass, clearly visible now, a ball of crimson and black some six hundred kilometres across, the irregular surface sculpted with toy landscapes, miniature mountain ranges, valleys. The gravity-field surveys had r
eported some immense object hidden inside the Cache. Well, here it was.

  Sensors poked out of the flitter’s hull, and Grantt, staring into his screens, devoured the data as they came in. ‘I’m detecting compounds in that air: carbon monoxide, methane . . . A very carbon-rich mix. Traces of water. A decent air pressure too. All of this was presumably manufactured at the Sun, transmuted from solar hydrogen and helium – or even just created direct from the radiative energy, I suppose, like the hull material. Of course, as per orders, we’re sending out a stream of messages of all kinds, from optical blinks to neutrino pulses. Hi, we’re friends! No response yet . . .’

  Poole, silent, looked outside.

  With the thrusters turned off now, they were falling slowly, slowly, into warm air. Above, Poole could see a tremendous flat roof, a panel of pale light like diffuse sunlight, with that hundred-metre breach above, a window of darkness through which stars gleamed. When Poole looked from side to side, through air that was dense, misty, he saw ragged clouds floating, and sparks descending, like shining raindrops. Without windows, presumably the hull plate itself was the source of interior light for this – environment. And for the heat, perhaps.

  Beyond the clouds he thought he saw more walls, the side faces of this cubical container, walls hundreds of kilometres away. Walls beyond the sky.

  Grantt shook his head. ‘So many marvels. The hull material, the membrane. The containment field over the lesion. Whatever transmutation technology was used to create all this in the first place. Technology so advanced it looks elementary, simple. Maybe miracles always do.’

  Poole was distracted. An angel was floating down past his view window.

  ‘Miracles . . .?’

  31

  It was a raindrop, as they had come to call them. An apparently perfect silvered sphere a few metres across.

  It really was not unlike the Wormhole Ghost that had come out of another universe to speak to him, Poole realised, but he had a deep intuition that that was just a coincidence of form: spherical shapes were robust, if you were containing pressure or trying to keep it out, and a silvered surface helped with thermal control . . . There was none of the sense of mass, of clumsiness, about this creature, as he had observed about the Ghost in those brief moments of contact. This was something far more advanced – or evolved.