He nodded to Cormac when he had finished, but Carn spoke out before Cormac could say anything.

‘What about the chain-cotton? Slightest mistake and you could lose an arm.’

‘No, I can’t demonstrate it here—wrong temperature—but out there the cotton will be coated with a speed-set foam as it comes out. The foam is stripped off when the line is wound in.’

Carn nodded, satisfied.

With little more to add, Cormac signalled that they go.

Outside the shuttle the air was pellucid even in the encroaching darkness. It seemed almost like a frosty morning and Cormac half expected to see vapour billowing from Aiden’s mouth. The temperature was 150 Kelvin, though, and if he had taken his mask off, his first breath would have frozen his lungs to a delicate glass sculpture that would have shattered on his next breath.

On the horizon the Andellan sun was a small copper coin on an off-white sheet. The place where they had landed, with the dark cloud sliding overhead, seemed almost to lie beneath some sort of overhang, so heavy was that cloud. Cento had put them down on a frozen lake of complex water ices, which now fluoresced as the heat from the shuttle raised them to the temperature where they made the transition to normal water-ice. It was a weird scene: the shuttle blackly silhouetted over those lights. Cormac turned away and saw that Carn was looking at the dim sun.

‘Morning here,’ Cormac told him. ‘At the installation it’s midday. One week solstan and it’ll be night there. Lot colder then.’

Carn nodded. ‘I’m aware of that. So’s Chaline. She’s getting impatient.’

Lugging equipment, they moved from the shuttle to the nearby shore of the lake. Here the slabs had fallen like stacks of coins, and in places had the appearance of curving staircases. Sitting on one of these slabs they pulled on grip shoes and the abseil equipment. The entrance to the shaft was only a short climb above them, over the crusted purplish rock. They reached it in ten minutes.

The mouth of the shaft was a perfect oval created by its angle into the flat ground. Either this area where it had been started was clear to begin with, or it had been specially cleared. Its walls were coated with a fine white powder of carbon-dioxide crystals streaked with the green of sulphate impurities. At the lip of the shaft Gant squatted and opened a box. Within were silver spheres stored like eggs in a tray.

‘I’ve pre-programmed them,’ he said, and took one from its packing. As soon as it was in his hand it glowed like a light bulb. He tossed it into the shaft. As soon as it was out of his hand it streaked away. ‘There are sixty in this box. The way I programmed them we’ll have one every thirty-five metres with a couple left over for the chamber itself.’