Phase Space. Stephen Baxter

and beyond. But it wasn’t working out like that. Sure, the gravity well colonies were in place, but they were hardly thriving; they were always going to be dependent on key volatiles shipped in from somewhere else. And they didn’t have much to trade; Ra could purchase high-grade metals much more cheaply from other rocks.

      There were actually more humans living in the rocks now than on the Moon or Mars. And Ra had more trade with other rocks than anybody else – even Earth …

      He saw there was one articulated joint on the splitter boom that was giving particular problems; its prophylactic cover had been taken off, revealing a knobby joint with big, easily replaced parts, already half-dismantled, like the knee joint of a T Rex.

      The youngsters were talking about more advances in technology. Like nanotech miners which would chomp their way through the rock without any human intervention at all. Greenberg kind of hoped it wouldn’t be for a while, though; he preferred machinery big enough to see, and wrestle with. It gave him a purpose, a reason to use the upper-body strength he’d brought up from Earth.

      The workers got out of the way of him, and, whistling, he moved into the balky joint with his vacuum line.

      Screw Mars, he thought as he worked; he liked it here.

       The remnant of the cloud moulded itself into a flattened, rotating disc. Solid particles condensed: ices of water and hydrocarbons in the cooler, outer rim, but only rocky debris in the hot, churning heart of the nebula. Planetesimals formed, massive, misshapen bodies that collided and accreted as they raced around the new sun.

       And, out of the collisions, planets grew: rocky worlds in the hot centre, volatile-fat giants further out. A powerful wind blew from the sun, violently ejecting the amniotic remnants of the birth cloud. Planetesimals rained down on the surfaces of the new worlds, leaving scars that would persist for billions of years.

       The gravity of young Jupiter plucked at the belt of planetesimals further in, preventing their coalescence into larger bodies. So, in the gap between Jupiter and Mars, the planetesimals survived as asteroids: rocky chunks closest to the sun, volatile-rich snowballs at the outer rim, moulded by impacts with each other, melted by radioactivity and electrical induction.

       And it was to the asteroids that the starship came: after billions of years drifting like a seed between the stars, still running from the supernova, exhausted, depleted, its ancient machinery cradling the generations that swarmed within, evolving, never understanding their plight.

      Scale: Exp 3

      The nanobugs woke him; with reluctance he swam up from dreams of sunlit days with his daughters on the beaches of Galveston.

      He emerged into a gritty, unwelcome reality. Here he was: half a man, with his whole lower body replaced by the gleaming box he called his PMU, pipes and tubes everywhere, still rattling around inside his clumsy old hab module.

      Not that there could be much left of his original home. That old NASA stuff had mostly worn out after a decade, let alone a thousand years. But the Weissmans, or anyhow the robots they’d assigned to keeping him alive, quietly rebuilt this old box around him, just as they rebuilt him continually, nanobugs crawling through his body while he slept away the years.

      Well, the hell with it. He dug out a packet of food – the label reassured him it was chicken soup, and as far as he was concerned that was what it was – and he shoved it into the rehydration drawer of his galley.

      He moved to a window, the little nitrogen reaction-control squirters on his PMU hissing softly. The window gave onto a shaft cut through the regolith, which had a massive lid that would swing down on him in case of a solar flare or some such. It gave him a good view of the surface of Ra-Shalom, and a slice of the night side of Earth, and a handful of stars.

      Water-blue light glared out of Ra.

      When he’d first come here, Ra had been just a lump of dirty carbonaceous stone. Now, the old craters and ravines transformed into a patchwork of windows, roofed over with some kind of smart membrane.

      Greenberg could see into the lens-like surface of one of the crater windows. And right now, a few minutes from the aerobraking of Toutatis, the Weissmans were swimming up from the big spherical ocean they were building in the hollowed-out interior of Ra, swimming up to watch a light show hardly any of them understood, probably.

      The Weissmans came in a variety of shapes. There were even still a few standard-issue four-limbed humans around. But the most common morphology was something like a mermaid, with the legs – useless, heavy distractions in microgravity – replaced by a kind of fish tail, useful for swimming around in the air, or the interior ocean. A lot of them had gills and never came out of the water at all, and some were covered in fur that streamlined and warmed their bodies.

      The Weissmans had done away with every part of the body which wasn’t needed in microgravity. And some had gone further. Some didn’t have hands, or arms. In an age of ubiquitous and one hundred per cent reliable machinery – machinery which could manufacture other machinery – human beings, it seemed, didn’t need to be toolmakers any more.

      To Greenberg, they looked like nothing so much as seals.

      It was their choice, or their progenitors anyhow. But what Greenberg couldn’t figure was what they did all day.

      Greenberg himself still had work to do, in these rare intervals of wakefulness: monitoring Ra’s external systems, checking the import of volatile and metal-rich cargoes.

      But maybe the Weissmans were just being kind. There were probably gigantic smart systems that backed up every action he took. He was a kind of museum piece, he supposed: the first human to rendezvous with an asteroid, all those years ago, a living totem for the Weissmans of Ra.

      He finished the soup and let go of the packet, and a domestic bot – a fussy little bastard like a trash can with attitude thrusters – came hissing out of its corner and grabbed the bag.

      Greenberg felt sour, grumpy and isolated.

      He studied Earth, which swam past on one of its closest approaches to the rock in years.

      He remembered from his first orbital missions aboard Shuttle, all those centuries ago, how the coastal rims of the continents would just glow with artificial light. Greenberg had supposed, then, that it would go on, that the Earth would just get richer and fatter and brighter.

      But it hadn’t worked out that way. Earth, in fact, grew darker every time he looked.

      Once the expansion into the near-Earth rocks had begun, it wasn’t long before a move further out followed: first to Phobos and Deimos, the captured asteroids that circled Mars, and then out into the main belt itself. Vesta, one of the biggest of the main belt rocks, had been the first to be extensively colonized, and now it was the hub of further expansion, little archipelagos of busy mines and colonization, scattered across the belt.

      And, so Greenberg understood, there were some pioneers who had gone even farther afield: to the comets out in the Oort Cloud, and the Kuiper Belt, where billions of ice moons the size of Ganymede swam through the darkness.

      Of course the techniques they used nowadays made Ra look primitive. Those universal fabricators, for instance, that sucked in asteroid ore at one end and pumped out whatever you wanted at the other, using something called molecular-beam epitaxy to spray atoms and molecules directly onto a substrate. Greenberg didn’t understand any of these new gadgets, even the stuff you could see.

      It was strange for Greenberg to remember now how much agonizing there had been when he was growing up about the depletion of Earth’s resources, the need to close the loops of mass and energy, as if Earth itself was one big CELSS. Nobody worried about that any more; the solar system had worked out to be just too rich in resources; those loops would stay open for a long time yet.

      It took a long time for the economics and demographics and such to work