He looked at her, his eyes narrow over his mask. “Figure it out. No sunlight for fourteen days.”

“Oh. The mud is going to freeze—”

“Geena, depending on the atmospheric dynamics, the air is probably going to freeze. For two weeks the Moon will be like it used to be, and we’re going to have to find some way to live through it.” He shrugged. “Or maybe we should just hole up inside our lava tube. We’ll have to think about it. As long as it doesn’t collapse, or flood. I sure don’t want to be caught out in the open when the sun goes down. There will be a wind from hell, all that air sweeping around from the hot side to the cold—”

“But the air will boil off after dawn.”

“Most of it. Some of it is going to collect back where it came from, the cold traps at the Poles. And it will stay there. Nothing has changed the basic geometry of the Moon, Geena. Eventually all this lovely air will finish up back where it started, back at the Poles… Somebody is going to have to figure out a way to stop that, some day.

“But that won’t be for a while. For now, the comet debris is still boiling off, powered by the Moonseed… I figure things won’t start to stabilize until all the ice has boiled off. Which will take a year, at least.” He squinted at the Earth. “Maybe they will send the first biogens. There’s no reason to delay. Photosynthetic plants, algae maybe, to start the job of turning all this sunlight and carbon dioxide to oxygen and food.”

“Henry, how long is all this—” she waved a hand “—going to last?”

“Well, even if we keep it from freezing at the Poles, long-term the atmosphere is going to leak away into space. But it’s a slow process. It’s like putting a bucket of water in the desert. Sure, the water evaporates, but it takes a long time because it can only get out through the comparatively small surface area of the top. In the same way the upper rim of the atmosphere will only allow the air to leak out slowly…”

She pulled at her mask, adjusting it. “Always the scientist. You tell me everything except what I want to know. How long is long term, Henry?”

He shrugged. “Maybe ten thousand years.”

She said gently, “Time enough to think of something else, then.”

“I guess so. Come on. Let’s go pack.”

Side by side, arguing, planning, they walked back towards the lava tube.

2

A year later…

She was in hospital when Henry returned from the Moon.

She hadn’t wanted it this way, but the tests had become overwhelming: the best American technology, X-rays and scans and ultrasound and blood tests, and a whole set of -scopies which left her bewildered, sore and humiliated: sigmoidoscopy, colonoscopy, gastroscopy, bronchoscopy, cystoscopy.