Moira looked a bit impatient. “What you are referring to as my lab bears the same relationship to a proper lab as some ones and zeroes on a thumb drive does to a living human. It is a collection of crated equipment that cannot even be unpacked and used in zero gravity. And even if we set it all up and turned it all on, it would be useless without a staff of Ph.D.-level molecular biologists.”

“Really? Useless?” Markus asked.

Moira sighed. “For small-scale work, one sample at a time, well, that is easier. But to reconstruct a genetically diverse human population—”

“But, Moira,” Markus said, “we cannot do that anyway until so many other things are in place. A large population cannot live in arklets eating algae. We need to establish a viable and safe colony first. Then, we build your lab. Then, we create a more diverse ecosystem: better food, greater stability. Only then do we even begin to worry about the heterozygosity of the human population. Until that time, we have more than enough people to create healthy non-inbred children just by the usual process of fucking each other.”

“That is all true,” Moira said.

“And that is the basis of my statement that the HGA was bullshit,” Markus concluded.

“You’re saying,” Doob said, “that if we had all of the prerequisites in place—the colony, the ecosystem, the talent—needed to actually exploit the HGA—”

“—we would no longer need it, yes, this is my point!” Markus said. “Can we please stop wasting time on it now?”

“How would you prefer to be spending time, Markus?” Moira asked, giving Markus an amused, owlish look through her glasses.

“Talking about how to get there. How to realize that situation we were just talking of.”

“And how might I contribute to that, given that the HGA is ninety-seven percent destroyed and none of my equipment will be usable for a long time?”

“I want to talk of preserving that equipment,” Markus said, “preserving it against all hazards, and then getting it to a safe situation where we can one day construct this laboratory you speak of.”

“It’s about as safe as we can make it, isn’t that so?” Moira asked. “It was given a sort of privileged position off of Node X—quite close to Amalthea. It’s not living dangerously, the way we are at the moment.”

She was referring to the notion, frequently discussed by Arkitects, of the Cone of Protection that supposedly existed in the lee of Amalthea. To the extent that the paths of incoming bolides were predictable, Amalthea could be pointed into them and used as a sort of battering ram. The forward surface of the asteroid would take a beating—but a solid slug of ancient nickel and iron could survive quite a lot. Anything situated up against its aft surface would be sheltered against virtually all hazards. But the protected zone did not, of course, stretch back infinitely far. The farther you lagged behind Amalthea, the more likely you were to get hit by a bolide coming in from an off angle. The Mining Colony was in the safest position, since, by its nature, it had to be right up against the asteroid. Almost as safe was the cluster of modules connected to Node X, immediately aft of the SCRUM, which was where all of Moira’s gear had been stashed. Behind that, the protected zone narrowed, a long acute cone, finally disappearing altogether somewhere aft of the Caboose. When Moira joked about “living dangerously” she referred to the fact that T3, the third torus, in which they were sitting now, was rather wide and rather far aft, placing it close to the limits of that cone. Efforts had been made to beef up its shielding, but it was still at higher risk than many other parts of Izzy.

Markus nodded. “Your stuff is pretty safe. But it would be safer if we moved it inside of Amalthea. I have talked to Dinah about it. She says that they could mine out cavities and store things of great importance there.”

A silence while Doob and Moira pondered it.

On one level, Markus’s proposal was perfectly obvious. Of course anything would be safer inside of a huge metal asteroid.

On another level, it had ramifications.

As of a few days ago—pre–White Sky, the last time anyone had been able to think straight—the fate of Amalthea and the Mining Colony had still been subject to debate. Was the asteroid the boulder in the wheelbarrow that had to be dumped? Or was it the aegis that would shelter the entire human race? The argument had come down to statistics. They just didn’t have enough data to make a decision.

By suggesting that Moira’s equipment be moved into the interior of Amalthea, Markus seemed to be committing to a specific course of action.

It was a course that Doob instinctively agreed with. But it was a bit strange for a man like Markus to just decide on a course of action before the numbers were in.

Or did he know something Doob didn’t?

Moira, in any case, went first. “What if we Dump and Run?”

She was referring to a gambit, frequently discussed and war-gamed, in which Amalthea would be cut loose and abandoned, and Izzy, lightweight but unprotected, would boost herself to a higher orbit with fewer bolides flying around in it.

“Then we would simply have to move all of that stuff back to Node X first,” Markus said. “Or wherever we felt was safest.”

This elicited a searching look from Moira. Markus held up his hands. “But I take your point. I am increasingly biased against Dump and Run.”

“You know how I feel about the Swarmamentalists,” Moira said.

She was referring to another of the basic gambits, Pure Swarm, in which everything—presumably including Moira’s lab—would be distributed among arklets, which would then collectively move to higher orbit. People and goods would move among them through a decentralized market-based economy.

“Listen,” Markus said, “now that everyone below is dead, and we don’t have to put up so much with bullshit, you will find that Hu and the others have a more nuanced view than they were letting on before.” He referred to the fact that Zhong Hu, as the foremost swarm theorist and the brains behind Parambulator, was assumed to be a Swarmamentalist.

Doob nodded. It still took some effort to remind himself that the millions of Internet commentators arguing for this or that strategy were all ghosts now.

“You know something,” Doob blurted out. Then, as the thought was coming into his head, he added, “From Dinah. The radio.”

“Yes,” Markus said. “Ymir is coming in hot, high, and heavy.” He surrounded those three words with air quotes.

“What does that mean?” Moira asked. “She’s made of ice, how can she be hot?”

“She is approaching with a high closing velocity. Not unmanageable. But . . . somewhat exciting.”

“And ‘high’?” Doob prompted him.

“Sean also transmitted his params,” Markus said. “It would seem that he did us a large favor. He executed the plane change while it was still easy to do so, way out around L1.”

“So when he says he’s coming in high,” Doob said, “he means that Ymir has a high orbital inclination—close to ours?”

“Very close to ours,” Markus confirmed. “He is dropping this big chunk of ice into our lap.”

“So,” Moira said, “on top of everything else, Sean Probst is now preparing to dive-bomb us with a comet?”

“A piece of one.”

“A big piece,” Doob guessed, “if he specified ‘heavy.’”

“The number was impressive.” As Markus said this, he shifted toward Doob and looked him in the eye.

“Oh wow,” Doob said. “Is it enough for the Big Ride?”

“If we can get Ymir to rendezvous with Izzy, then yes,” Markus said. “It is more than enough.”

The Big Ride was the third of the basic options. It meant to boost Izzy in its entirety—Amalthea and all—to a much higher orbit. It had been considered implausible because of the amount of propellant that would be needed. Not just implausible but—absent the timely return of Ymir—physically impossible. Despairing of Sean’s chances, its supporters had lately tended to suggest scaled-down variants, such as reshaping a small percentage of Amalthea into bolide deflectors and ditching most of its mass.