The pressure vessel — the heart of the probe — had hatched out of its aeroshell and cut itself loose from its parachute. The probe was still more than twenty-five miles high, but it had already cut away its last chute. The air of Venus was so thick that from where it was the probe could free-fall all the way to the surface.

The pressure vessel was a sphere of thick metal. There were vanes on the sphere to make it spin, so that it was stabilized during its fall, and there were tough little windows cut into the surface so that the probe’s instruments could see out.

“Hey,” Gershon said. “Look at these numbers from the mass spectrometer.” He tapped a screen. “I got me some heavy isotopes of hydrogen in the air.”

“So what?”

He narrowed his eyes. “Water, my dear. Oceans, maybe: once upon a time, anyhow. Long since boiled off by the greenhouse effect, caused by all this fucking CO2. But where there were oceans…”

Life, perhaps.

The probe was spinning slowly in the sluggish air. The light was dark, reddish, but the illumination was no worse than a cloudy day on Earth. She couldn’t see the sun at all; there was only an ill-defined glare, almost baleful, spread across half of the cloud bank that covered the sky.

And suddenly she could see the surface: the probe’s fish-eye camera returned panoramic views of a landscape, dimly visible through the murky air. York made out what looked like a cleft in the land, running from side to side of the picture — no, not a cleft, she realized; it was a ridge, hundreds of miles long, leading up to a plateau.

“Wind speed down to zip,” Gershon said. “Pressure and temperature still rising. Venus doesn’t have air; that stuff is more like my momma’s chicken soup.” He tapped the screen. “That’s Ishtar Terra,” he said. “Or the edge of it; right where we’re drifting. We’re slap on course. Look at it, Natalie. Seven miles above the mean surface, and—”

“ — and as big as the United States. I know.” Ishtar Terra was a high, exposed plateau, already mapped by radar from Earth: Ishtar was how a continent might look if someone drained away Earth’s oceans.

York felt excitement mount. At last, a chance to do some geology on this mission.

Venus and Earth were twins. So presumably Venus had a hot, radioactive core, just like Earth’s, whose heat must escape to space. On Earth, that happened in two ways: plate tectonics and vulcanism. But, in the radar mapping and the crude Russian probes’ results, nobody had observed any sign of plate tectonics on Venus: no rings of vulcanism, no rift valleys.