So York, along with every other geologist, believed that the dominant geological process for losing core heat had to be vulcanism: ongoing and continuing. There just had to be a whole bunch of live volcanic hot spots, all around the planet, feeding the heat to the atmosphere, and thence to the ultimate heat sink of space. Therefore, at Ishtar, she expected to see a young surface, heavily distorted by the upwelling of magma — liquid rock under the solid crust — and resurfaced by repeated lava flows. If there were any impact craters, they would be heavily distorted, maybe even buried, invisible under the fresh surface.

She pointed off to the right of the screen, to shadowy cones that loomed out of the murk. “Look at that. That must be the Maxwell Montes.” The tallest mountain range on Venus. The probe was drifting toward the Montes, she saw, floating like a fat metal balloon in some sluggish current. The Montes were steeper, in places, than anything on Earth. The mountains were folds in the surface, illuminated by the diffuse, ruddy light and wreathed by thick air; it was like swimming over some undersea ridge.

Something showed up on the edge of the screen: a circular feature, on the flank of the mountain range.

“Hey. What’s that?” The probe’s slow rotation took the feature out of shot, almost immediately. “Hot damn.”

Gershon grinned up at her. “Sorry,” he said. “No panning or zooming. This isn’t Wide World of Sports.”

A circle? Could it be a crater? What the hell was that doing there?

Something was wrong; York could smell it. She waited, excited, impatient, as the camera panned around, agonizingly slowly, the image wobbling as the probe hit turbulence pockets in the soupy air.

The circular feature came back again, drifting in from the right.

York shoved her face right up to the screen. Almost a perfect circle, surrounded by a dark blanket of material: it had to be an impact crater, surrounded by a layer of ejecta. Like a bullet hole centered in dried blood. And it was so large it was almost certainly several hundred million years old.

And it was pristine, no coverage by lava flows, no distortion by shifts in the landscape.

Which meant that Ishtar Terra had to have been geologically dead, too, for at least as long.

That’s impossible. Her mind raced. If that’s characteristic of the whole surface, everything is turned on its head. No plate tectonics, and no vulcanism either?

The enigmatic crater passed out of view as the probe descended.

“Ten minutes from pericenter,” Stone said. The mission commander was watching his instruments, York saw, not the images from the probe, the first pictures of the surface of Venus.

The probe was heading for a rough plain, broken up with large, jagged rocks. She saw some evidence of winds: dust streaks, scouring, a couple of flattened dunes. The air isn’t always so sluggish, then.