The cap of steam was much brighter, area for area, than the native surface of the Moon, which was starting to look drab by comparison. Earth’s reflective clouds of water vapour made it one of the brightest objects in the Solar System. And already, with maybe twenty per cent of the Moon’s surface covered, the Moon was much brighter than before…

He looked away from the eyepiece. He was slightly dazzled. When he looked down, the shadow of his liver-spotted hands against his shirt was much sharper than before.

Sixt was staring up at the Moon, its new light shining on his bare scalp. “My God,” he said. “You guys going up there, hopping around for three days, that was something. But now we’re changing the face of the Solar System. My God.”

Jays found he was trembling. Lights in the sky. He wanted to cower, hide like a dog under Edwin Hubble’s chair.

Henry — restless, excited — walked until he came to a rise, which he climbed in a few loping paces, and looked south.

The undulating lunar surface stretched away before him, its surface shaped by fractal crater layers into a frozen rocky sea. The sun was to his left — the east, for even after all that had happened it was still morning on the Moon — and he could feel the touch of its heat, through the thick layers of his suit. And the Earth was before him, a blue crescent: it was an old Earth, its phase locked in opposition to the new Moon’s. He imagined human faces all over that night side, turned up towards him, watching the Moon.

The sky above was still black, unmarked by the great events which ought to be occurring on the other side of the planet.

Ought to be.

All those volatiles were going to spread around the curve of the Moon.

How quickly?

The leading edge, spreading into vacuum, would diffuse as rapidly as molecules moved at such temperatures — say, a thousand miles an hour. Enough to cloak the Moon in cloud, from pole to pole, in three or four hours.

That was his theory, such as it was.

He was looking south, away from the Aristarchus Complex, over the extent of the Oceanus Procellarum, the Ocean of Storms. The way it would come.

The released vapour, like heavy fog, would rush into the low-lying areas first. It would have to flow around the big bright block of the lunar highlands to the south, the Apennine and Altai Mountains, and then gush down into the lower-lying maria. Much of the left-hand side of the visible face of the Moon, as seen from Earth, was pocked with grey maria, including the place he was standing now, on the invisible line between Procellarum and the Mare Imbrium. The volatiles would just gush across these immense grey plains, as the thin basalt lava had once flowed, a billion years before. Maybe, he thought, the new weather was going to reach him sooner than he expected.

It was indeed a judo trick.

His single bomb, no matter how precisely delivered, could never have melted enough of the putative volatiles at the Poles to make a difference. There hadn’t been enough energy in the nuke to melt more than that initial hundred-yard spherical chamber in the dust. But his intention was to achieve more than that: much more.

To melt all the volatiles he believed were locked at the South Pole would need something of the order of a billion times the energy released by his nuke. One hell of a feedback factor.

But the energy he needed was there: superstring energy, locked up in the inert Moonseed, which permeated the aluminum-rich rock that was the crust of the Moon.

Henry had modelled it over and over.

Elsewhere on the Moon, there was no evidence of Moonseed in the upper layers of the regolith. Presumably the action of sunlight had long ago activated whatever was there to activate; only shadowed rocks, like 86047, retained infection. And deeper in, the Witch in the Well had suppressed any chain reaction that might have led to the disassembly of the Moon.

The gamma-ray flash from the nuke would, he figured, start a chain reaction in the deep-buried Moonseed. It would be activated in the upper layers of the crust, to a sufficient depth that there would be enough energy released to melt his volatiles — so he figured — before the chain-reaction reached the deeper crust layers and was suppressed by the Witch.

So he figured. His lack of data, particularly on the suppression mechanism, was a little worrying.

He looked at the black, inert horizon. Nothing might happen at all. Or, he might just have destroyed the Moon. I’ll settle for anything in between…

It was a little spooky, in fact, the way the Moonseed had configured itself to offer him this mechanism. A lever, with which to move a planet.

Terraforming the Moon would have been possible without this bizarre partnership with the Moonseed, and it had been Henry’s vision — what he had hoped to prove with Shoemaker — that the Moon had sufficient resources one day to become a true sister planet to Earth.

They could have done it anyhow. But it would take a long time before humans could assemble the energy required. Centuries, even millennia.

The Moonseed infestation seemed curiously designed. It was as if it was meant to be like this. The Alfred Synge cosmic conspiracy theory.

Maybe he was being foolish, to be out in the open at a time like this. Or maybe he wasn’t. Who could tell? Nobody had sat through a terraforming before. Maybe nobody ever would get the chance again…

But now there was something in the sky.

He raised his gold sun-visor. The unwavering sun beamed in on him, shining in his eyes like a spotlight. But he masked his eyes with his gloved hands, holding them over his plexiglass visor, in a tunnel before his eyes. He stared out, letting his eyes dark-adapt once more.

Gradually, the stars came out for him, over the Ocean of Storms.

But those pinpoint lights were flickering, he saw: for the first time since the last of its internal atmosphere was lost to space, the stars in the Moon’s sky were twinkling.

There was air up there.

The old surface, where it was still exposed, was looking dingy grey by comparison with the glowing mask of cloud; and that diminishing cap was crowded, even as Jays watched, by the rippling ring of cloud that closed around it.

It must almost have reached Meacher and Bourne, he thought. They would see it any time now.

He envied them. Christ, to be there now…

“I knew it from the moment I picked up that damn rock,” he said.

“Knew what?” Sixt asked, sounding puzzled.

“That there was something in that rock.” And he told Sixt about the dust pool he’d seen on the Moon, the way his purloined fragment of bedrock had glowed in the sun.

Sixt said, “You knew? Christ, man, if you’d said something—”

“We might have avoided all this?” Jays shrugged. “Maybe. But if I’d reported something as crazy as that, they wouldn’t have let me fly again. What would you have done?”

Sixt mulled it over. “What you did. I guess you shouldn’t blame yourself. The damn thing is a planetary plague. It would have gotten here anyhow.”

“The irony is I never flew again anyhow. Maybe there is a just God. What do you think?”

The Moon glowed in the sky, already as bright as a new sun; even the darkened crescent to its western limb was clearly visible. It was almost featureless, so bright was it now; but Jays thought he could make out a bright triangle in the south-east — the old highland area, poking above much of the new atmosphere — and perhaps dim shadows of the old maria. Here and there on the new, bland face of the Moon, he could see the crackle of lightning: gigantic storms which must have straddled hundreds of miles, with lightning leaping between clouds, illuminating them from beneath, as if the planet’s surface itself was cracking.