So they voted to allow the space elevator to remain standing, for the time being— and in the possession of UNTA, down to and including the Socket, without contestation. It was like King Canute deciding to declare the tide legal after all, but no one laughed except Ann. The other Reds were furious. Ownership of the Socket was still being actively contested, Dao objected loudly, the neighborhood around it was vulnerable and could be taken, there was no reason to back off like this, they were only trying to sweep a problem under the rug because it was hard! But the majority were in agreement. The cable should remain.

• • •

Ann felt the old urge: escape. Tents and trains, people, the little Manhattan skyline of Sheffield against the south rim, the summit basalt all torn and flattened and paved over . . . There was a piste all the way around the rim, but the western side of the caldera was very nearly uninhabited. So Ann got in one of the smallest Red rovers, and drove around the rim counterclockwise, just inside the piste, until she came to a little meteorological station, where she parked the rover and went out through its lock, moving stiffly in a walker that was much like the ones they had gone out in during the first years.

She was a kilometer or two away from the rim’s edge. She walked slowly east toward it, stumbling once or twice before she started to pay proper attention. The old lava on the flat expanse of the broad rim was smooth and dark in some places, rough and lighter in others. By the time she approached the edge she was in full areologist mode, doing a boulder ballet she could sustain all day, attuned to every knob and crack underfoot. And this was a good thing, because near the rim’s drop-off the land collapsed in a series of narrow curving ledges, the drops sometimes a step, sometimes taller than she was. And always the growing sense of empty air ahead, as the far side of the caldera and the rest of the great circle became visible. And then she was climbing down onto the last ledge, a bench only some five meters wide, with a curved back wall, shoulder-high: and below her dropped the great round chasm of Pavonis.

This caldera was one of the geological marvels of the solar system, a hole forty-five kilometers across and a full five kilometers deep, and almost perfectly regular in every way— circular, flat-floored, almost vertically walled— a perfect cylinder of space, cut into the volcano like a rock sampler’s coring. None of the other three big calderas even approached this simplicity of form; Ascraeus and Olympus were complicated palimpsests of overlapping rings, while the very broad shallow caldera of Arsia was roughly circular, but shattered in every way. Pavonis alone was a regular cylinder: the Platonic ideal of a volcanic caldera.