He stepped gingerly onto the metal surface. It was slick, and littered with bits of loose frost, but it was easier than walking on the ice. He sensed hollowness beneath his feet, though, a great volume, and he trod lightly, for fear of making a noise. He knelt down, pressed his palm to the metal surface, and waited. Where his knee touched the metal he could feel its cold, clawing at him through the diamond pattern of heating filaments in his skinsuit. It took a few seconds for results from his suit’s sensors to be displayed, in hovering Virtuals before his face.

He was rewarded with a sketchy three-dimensional cross section. The metal plate was a couple of yards thick, and much of it was solid, fused on a base of rock. But it contained a hollow chamber, an upright cylinder. Probably some kind of low-tech backup system. The covering for the hollow was no more than a couple of yards away.

He walked that way and knelt again. His fingers, scraping over the sheer surface, quickly found a loose panel. By pressing on one side of it, he made it flip up. Beneath that was a simple handle, T-shaped. He grasped this, tugged. A lid rose up, attached by mechanical hinges.

Abil peered into the pit, using his suit lights. The pit was a little deeper than he was tall. He saw a wheel in there, a wheel set on a kind of spindle. Its purpose was obvious.

Dower came to stand beside him. She grunted. “Well done, Corporal. Okay, let’s take a minute. Check your kit again.” The troopers, working in pairs, complied.

Dower pointed at the mountain. “You were right—uh, Denh. The mountain’s tectonic, not impact-created. We’re standing over a midocean ridge: a place where the crust is cracking open, and stuff from within wells up to form new ocean floor. And where that happens, you get mountains heaping up, like this. On this planet it’s still happening. The loss of the sun destroyed the surface and the air, but it made no difference to what’s going on down deep. All along this ridge you will have vents, like valves, where the heat and the minerals from within the planet come bubbling up. And that heat will keep little pockets of water liquid, even now. And where there’s liquid water—”

“There’s life.” That mumble came from a number of voices. It was a slogan from biology classes taught to five-year-olds, all across the Expansion.