He put on his blue coveralls, regolith-stained gloves and Moon boots. He checked over his POS, his portable oxygen system. There were straps for him to fix the pack to his chest, and more to tie on his scuba-diver mask. There was the smell of rubber, of stale sweat, inside the mask; and immediately he put it on it started to mist up.

Geena watched him. Behind her, their lunar surface suits lay abandoned in a corner, greyed fabric sagging, like two fat men slumping side by side; Henry’s fishbowl helmet stared at him accusingly from where he had dumped it.

She said, “You sure this is going to be enough?”

“I’m sure. Believe me. Haven’t I been right so far?”

“About the Moon, maybe.”

He eyed her. They were going to be stranded together here for a while yet.

“I think we need to get out of here before we kill each other,” he said.

“Amen to that.”

Geena ran one last check of the shelter’s systems, and then followed Henry out of the cramped airlock. They carried their comms unit between them.

Henry looked up from the base of the rille. Before the nuke, he recalled, he’d been able to see stars up there.

Now, things were different. Now, the narrow rille was roofed over by a slab of grey sky, fat with cumulus clouds that looked low enough to touch. The murky light diffused down over the walls of the rille, and his blue coverall.

It was still raining, in fact, a slow drizzle of fat drops that hammered on his POS faceplate and rapidly soaked into his coverall.

But he wasn’t cold. In fact the air was hot.

…But it was thin, just a layer of carbon dioxide, nitrogen, water vapour and trace gases amounting to maybe a sixth of Earth’s atmospheric pressure. Like a mountaintop.

You wouldn’t want it much thicker, in fact. The gravity was one-sixth G, so to get the same air pressure as Earth you’d need a column height six times that of Earth’s. And then you’d suffer from a lot of haze and a greenhouse effect, all that cee-oh-two trapping excessive heat.

So, thin and dry was best, just the way it should be. It was as if they had been transported to the summit of a mountain two hundred and forty thousand miles tall, wrapped in comet air.

When he took a step, he squelched in red-brown mud. It was soaked regolith. He could swear the rille was a little deeper than it had been before — well, perhaps it was; perhaps the deeper regolith layers had collapsed. After a couple of steps it was hard to lift his boots, low gravity or not, so caked were they in clinging lunar mud.