When the science station was set up, he stepped back from it, towards the edge of the basalt ledge. He ran his eye over the connections one more time, making sure he hadn’t missed something dumb, checking all the power lights were switched on. He didn’t want to have to come back down here and fix anything.

However, it all looked fine. Now all he had to do was climb out of here, trailing a comms link cable behind him, so the station could talk to the surface, and so to Earth and the shelter.

But there seemed to be a softness, beneath the tread of his right foot.

He looked down sharply. He was maybe four feet from the lip. But suddenly the rock surface was crumbling like wet sand.

The last three or four feet of the ledge just disappeared, in a half-circle extending maybe a yard around him. Under a surface of some kind of duricrust, he realized, this whole ledge was rotten with Moonseed dust. Suddenly he was falling, amid a cloud of dust, and there wasn’t a damn thing he could do about it.

Moonseed sparkled in the light of his torch.

Falling on the Moon:

Dreamlike slowness.

In the first second — the first one or two rattled heartbeats — he only fell through a couple of feet. He fell stiffly, his suit starfishing around him, as if he was in some body-shaped coffin.

Two seconds, and, picking up speed inexorably, he had fallen ten feet. The rope was coiling behind him, still fixed to his waist. How much was there left? Enough to stop him hitting the Moonseed river?

Would he just drag his anchor rock off the lip of the rille after him?

Three seconds, maybe twenty feet, and at last his speed was becoming respectable. No air here, so no terminal velocity; if there was a hole all the way to the centre of the Moon you would just keep on falling, accelerating steadily, until—

His feet hit the surface of the Moonseed river.

It worked its way up his legs, to his waist, sluggish ripples spreading out from him. His speed slowed rapidly as the resistance of the dust built up. He could feel the pressure of the dust on his legs, crumpling the inflated pressure suit.

Now he was sinking slowly, as if into treacle. He tried to keep his arms out.

Up to his waist. He couldn’t move his legs.

He would presumably reach some level at which he would be buoyant. The dust was all but a fluid; Archimedes” principle would work, even here. How deep would that be? So deep that the pressure of the dust would crack his visor, ramming itself into his mouth and nose and eyes? Or maybe the end would be less spectacular: eventually, the heat trapped by the dust would surely kill him… The dust was up to his chest now. But his rate of descent was slowing. He tried to kick at the dust; maybe if he could lie on his back he could float like a swimmer on the Dead Sea. But he couldn’t move his legs, not so much as an inch; it was as if his pressure suit was embedded in concrete.