He showed her surface images, craters and domes and valleys and mountains, constructed from a radar survey by the Magellan spacecraft. “Venus was covered by volcanism. There were flood lavas and volcanic cones and domes, and other features which don’t have any analogues on Earth. We didn’t see plate tectonics, like Earth; we think Venus was a one-plate planet dominated by hot-spot volcanism. My favourite hypothesis is that there was a catastrophic global resurfacing every half-billion years.”

“A what?”

“The crust melting, globally. There are problems with the heat flow from the interior otherwise… It would be like five hundred million years of geology crammed into a few centuries. Now,” he said. “After. An image taken by the Hubble this morning.”

There was no evidence of a spherical shape. She made out a crudely-defined, blurred oval, with extensive tails, like a comet’s.

Alfred said, “You’re looking at a cloud of atmospheric gas, mostly frozen, and ground-up rock.”

“The rock’s from the surface?”

“Mostly the mantle, as far as we can tell. Most of the mass is still concentrated near the point where the centre of gravity of the planet used to be. We tried radar pulses from Arecibo, and… Well. Monica, we can’t find a solid object there any more. The substance of the planet is spreading out along the orbit. The ring probably won’t stay stable; the perturbation by Earth’s gravity will—”

“Hold it. Alfred, I can’t follow you. You’re saying that Venus no longer exists.”

“Not as a coherent solid, no.”

“That’s impossible. How much energy would it take to destroy a planet?

He considered. “Well, roughly speaking, you would have to lift every piece of rock to escape velocity, out of Venus’s own gravity well. There’s a quantity called the gravitational binding energy… For Venus, which had eighty per cent of Earth’s mass, it works out as ten to power thirty-two joules — umm, something like a thousand billion times our nuclear arsenal.”

“Just for the record, we aren’t talking about your global volcanic resurfacing here, are we?”

He smiled. “Even that would be quite a spectacle, if it occurred in the lifetime of this astronomer. But no, it’s orders of magnitude beyond that.” He rubbed his nose, smearing the gaudy sun block there. “Those are big numbers. But there’s another way of looking at it. If you consider the energy density required, averaged over the planet’s volume, it isn’t so high. Something like a tanker of gas per cubic yard or so, I guess.”

“What are you telling me?”

“We think we are looking at some funny physics over there, Monica. Which is why you and the rest of the particle physicists are going to have to work on this with us.”

“Funny physics?”