Incredible, he thought; he was still standing in vacuum, but he was looking at a layer of atmosphere, from the outside. He could see how turbulent it was: wherever it touched the ground, two hundred degrees hot, it was soaking up rock heat and boiling afresh.

On the Moon’s dark side — in shadow — it would be different. There, the ground was two hundred below freezing; there, over the high cratered plains of farside, good God, it must already be snowing.

The turbulent gas was picking up dust. That stuff could be a problem if it scoured at the seams of his suit.

But it advanced towards him ferociously, turning into a towering tsunami of gas and steam and dust, coming at him at a thousand miles an hour — more than the speed of sound, back on Earth.

He had time to look down, once more, at the ancient, complex surface of the regolith, his own boot print there, as sharp as Armstrong’s.

Geena is going to kill me for not being in the shelter, he thought. But he couldn’t have missed this.

The new air was white, and as tall as the sky.

Then it was on him, a wall of vapour sweeping over him.

It hit him harder than he’d expected, like a fire hose battering him from head to foot, a wall of rushing steam… Sound, on the Moon: he could hear the howling of this primordial wind across the plain, around his suit, the first sound in four billion years. The dust at his feet fled towards the vacuum, tiny dunes piling up over his blue Moon boots. There was a continual patter, almost like rain; it was probably pebble-sized fragments of regolith, trying to smash through his helmet. He tried to lift his arms, to protect his face, but he couldn’t.

He fell backwards.

He bounced on Geena’s backpack and rolled sideways, and skidded a few feet over the surface. He tried to shield the control panel of his suit, protect the backpack itself; but he was just scrabbling in the dirt like an animal, helpless before this planetary violence. And it was hot, Jesus, but after all he was in a jet of live steam.

He looked up. There was structure to the air already, he saw: the thick, ground-level fog, clearer air above, and, masking the vanishing remnants of black sky, some high, racing cirrus clouds: not billowing, just banner-like streamers. Perhaps they were ice crystals.

The air closed over him, like fog.

There were waves in the still-tenuous gas encasing him — huge density waves pulsing past him — and his vision periodically cleared, affording him glimpses of the sky.