“And what about the laws of thermodynamics? What about information flow? How do these assemblers get their information about which atom is where, in order to manipulate them? How do they know where they are themselves, to get from their tiny supply depots to wherever they are supposed to be working? How do they get their power for breaking up material, and navigating, and computing?” He turned to Bromwich. “Admiral, this is just more nonsense. Nanotechnology is cargo cult science. A plot generator for lazy sci-fi writers. Nobody has demonstrated any of this, outside computer simulations, where of course you can do anything you like.”

Evidently, Monica thought, watching him, the good doctor has a beef against nanotech. She wondered which grant application of his had been turned down in favour of some sexy nano-proposal.

Henry said mildly, “I’m not here to defend nanotech. The Moonseed, however, is doing one simple thing: building inward, and smaller. The structure, in fact, seems to be similar on all scales. You don’t need much stored information, or computation, or materials transfer to achieve that.”

The Admiral frowned. “I wish you scientist types wouldn’t argue with each other. So the Moonseed is some kind of artificial phenomenon. We’re looking at tiny machines here. Is that what you’re saying?”

Henry said, “Maybe they are artificial. Maybe they are alive. It may be that when a life form is sufficiently advanced, there is no difference. It may not matter anyhow.”

Bromwich shook her head, visibly angry, dissatisfied at the speculation and lack of clarity. “Continue with your analysis,” she told Henry. “What’s this thing for? What’s the point of rebuilding a rock?”

“Concentration of energy,” Henry said.

“What?”

“There is enough chemical energy in a tank of gasoline to achieve unified-theory levels of energy density — if all the energy could be applied to a single proton. Which we can’t achieve. We build colliding accelerators miles long to try to emulate that, but we don’t even come close, not within orders of magnitude.”

Bromwich pulled her lip. “You’re saying these little critters turn lumps of rock into — uh — miniature particle accelerators.”

“That’s exactly it, Admiral.”

Henry showed images from Edinburgh, exploding rocks around a volcanic plug called Arthur’s Seat, evidence from the lab where Apollo sample 86047 had exploded.

“The contaminated rocks achieve densities, towards the centre, at which fusion processes, at least, can occur. When the Moonseed destroys a chunk of rock, the outcome is dust, and a flood of high-energy radiation, and more Moonseed. It’s a way of propagating.”

“Mini nukes?” asked the Admiral.

“Yes.”

“What do you mean, at least fusion?”

This was Monica’s speciality. “He means the Moonseed constructs may reach greater levels of force unification than just fusion.”

“We’ve also observed this astronomically, now we’ve started looking,” Alfred said. “In the Earth-Moon system. The same radiation signature as on the ground. There seems to be a concentration of Moonseed at the Lagrange points.” He looked around the table for understanding. “Lagrange points are gravitationally stable collection points in the Earth-Moon system. We always wondered why we couldn’t see anything at the Lagrange points: no minor bodies, asteroids, trapped there. Now we know. The Moonseed is there, destroying whatever drifts in.”

“Just here? Where else?” Bromwich asked.

“Venus,” said Alfred Synge bluntly.

“Maybe space is their natural habitat,” Henry said. “Rather than planets. Our models show that they have difficulty reaching the surface of a planet, from space. They burn up in atmospheres, or are smashed by simple impact, on an airless body like the Moon.”

Alfred said, “But if they do get to a planet—”

“If they do,” Henry said, “then they transform it. Like Venus.”

Petit said drily, “Explain something else to me. You say the planets are shielded from the Moonseed, by atmosphere and gravity. We brought it here, from the Moon. But how did it get to Venus?”

“We’ve developed a theory about that too,” said Henry.

Petit said drily, “I thought you might.”

“We took it there,” Henry said.

“What?”

“You need a soft landing to deliver Moonseed to a planetary surface. The only objects which have soft-landed on the planets are our probes.”

“You’re saying we did this?”

Henry shrugged. “It’s a hypothesis. The probes collected the dust from the Lagrange clouds in near-Earth space. Specks in the paint work. And then delivered them to the planetary surfaces.”

Petit pulled Henry’s laptop towards him. “Give me a minute… Ah. The first probe to soft-land on Venus was Soviet. Venera 7. Landed in 1970.” He looked up.

“So,” Alfred said softly, “it takes a few decades to destroy a world the size of Venus.”

The Admiral snapped, “How big is Venus?”

“Similar to Earth,” Alfred said. “Eighty per cent of the mass.”

“Jesus H — So there’s our timescale.”

“Oh, this is just bull,” Petit protested. “For God’s sake. There are holes in this you can drive a Chevy through. We’ve also been to Mars. Mars is only eleven per cent of Earth’s mass. How come we didn’t destroy Mars too? And we know it’s on the Moon. How come the Moon hasn’t burst like a party balloon?”

“I don’t know,” Henry said, looking determined. “But I think that’s the key, Professor Petit. The Moon. The Moon is the key.”

Monica asked, “The key? To what?”

But Alfred was speculating again. “You know, you’re right, Dr Meacher. The only way the Moonseed can get to a planetary surface is through the action of intelligence.”

“Which means—”

“Maybe that’s the purpose of intelligence. Maybe we were meant…”

There was a moment of silence.

Petit laughed. “Alien nano robots manipulating history, eh? Is that what you’re going to tell the President? Should she go on TV with that? Admiral Bromwich, I intend to disprove this absurd scaremongering hypothesis, point by point.”

Henry nodded. “Do it. I’ll be there to applaud you.”

“But in the meantime,” the Admiral said, “we have to consider how to advise the President. And Dr Meacher, for all he’s a little swivel-eyed for my taste, is the only one coming up with any scenarios here.”

“Thank you,” Henry said drily.

Bromwich said, “I think we have to work on a worst-case assumption.”

Petit laughed. “The worst case being the end of the world. In an election year, too.”

Admiral Bromwich turned to Henry. “You’ve told me how bad this is going to get. Now tell me what we should do about it.”

“Three things,” Henry said. “We know we can slow the Moonseed down, if not stop it altogether, at least before it gets into the mantle.”

“How?”

“The structures it forms are fragile. They can be smashed, to put it bluntly.”

“We’ll bomb the shit out of it,” the Admiral said.

“And,” Petit said, “when you run out of bombs?”

“Then I’ll be on the White House lawn ripping it apart with my teeth and bare hands,” the Admiral said. “Where will you be? What else, Dr Meacher?”

Henry said, “Maybe we can come up with some kind of nano counter-agent.”

“I thought you said there was no hope of that.”

“I might be wrong. We have to try. But, no, I don’t think there is any hope.”

He let that hang in the air, for long seconds, maximizing its impact.

Monica studied Henry anew. He was the first to understand this, she thought. There must have been a time, right at the beginning, when only he knew this. Only he, of all the billions on the planet, could see the future. The unfolding of Moonseed logic: Christ, the end of the world. How must that have felt?

Probably, she thought, much like the moment when the doctor, an absurdly young man, had told her, in cool, compassionate terms, that she had such a short time left to live.