High above northern Maine, a G4 jet continued speeding toward Washington. Onboard, Michael Tolland and Corky Marlinson looked on as Rachel Sexton began to explain her theory for why there might be increased hydrogen ions in the fusion crust of the meteorite.

“NASA has a private test facility called Plum Brook Station,” Rachel explained, hardly able to believe she was going to talk about this. Sharing classified information out of protocol was not something she had ever done, but considering the circumstances, Tolland and Corky had a right to know this. “Plum Brook is essentially a test chamber for NASA’s most radical new engine systems. Two years ago I wrote a gist about a new design NASA was testing there‑something called an expander cycle engine.”

Corky eyed her suspiciously. “Expander cycle engines are still in the theoretical stage. On paper. Nobody’s actually testing. That’s decades away.”

Rachel shook her head. “Sorry, Corky. NASA has prototypes. They’re testing.”

“What?” Corky looked skeptical. “ECE’s run on liquid oxygen‑hydrogen, which freezes in space, making the engine worthless to NASA. They said they were not even going to try to build an ECE until they overcame the freezing fuel problem.”

“They overcame it. They got rid of the oxygen and turned the fuel into a ’slush‑hydrogen’ mixture, which is some kind of cryogenic fuel consisting of pure hydrogen in a semifrozen state. It’s very powerful and very clean burning. It’s also a contender for the propulsion system if NASA runs missions to Mars.”

Corky looked amazed. “This can’t be true.”

“It better be true,” Rachel said. “I wrote a brief about it for the President. My boss was up in arms because NASA wanted to publicly announce slush‑hydrogen as a big success, and Pickering wanted the White House to force NASA to keep slush‑hydrogen classified.”

“Why?”

“Not important,” Rachel said, having no intention of sharing more secrets than she had to. The truth was that Pickering’s desire to classify slush‑hydrogen’s success was to fight a growing national security concern few knew existed‑the alarming expansion of China’s space technology. The Chinese were currently developing a deadly “for‑hire” launch platform, which they intended to rent out to high bidders, most of whom would be U.S. enemies. The implications for U.S. security were devastating. Fortunately, the NRO knew China was pursuing a doomed propulsion‑fuel model for their launch platform, and Pickering saw no reason to tip them off about NASA’s more promising slush‑hydrogen propellant.

“So,” Tolland said, looking uneasy, “you’re saying NASA has a clean‑burning propulsion system that runs on pure hydrogen?”

Rachel nodded. “I don’t have figures, but the exhaust temperatures of these engines are apparently several times hotter than anything ever before developed. They’re requiring NASA to develop all kinds of new nozzle materials.” She paused. “A large rock, placed behind one of these slush‑hydrogen engines, would be scalded by a hydrogen‑rich blast of exhaust fire coming out at an unprecedented temperature. You’d get quite a fusion crust.”

“Come on now!” Corky said. “Are we back to the fake meteorite scenario?”

Tolland seemed suddenly intrigued. “Actually, that’s quite an idea. The setup would be more or less like leaving a boulder on the launchpad under the space shuttle during liftoff.”

“God save me,” Corky muttered. “I’m airborne with idiots.”

“Corky,” Tolland said. “Hypothetically speaking, a rock placed in an exhaust field would exhibit similar burn features to one that fell through the atmosphere, wouldn’t it? You’d have the same directional striations and backflow of the melting material.”

Corky grunted. “I suppose.”

“And Rachel’s clean‑burning hydrogen fuel would leave no chemical residue. Only hydrogen. Increased levels of hydrogen ions in the fusion pocking.”

Corky rolled his eyes. “Look, if one of these ECE engines actually exists, and runs on slush‑hydrogen, I suppose what you’re talking about is possible. But it’s extremely far‑fetched.”

“Why?” Tolland asked. “The process seems fairly simple.”

Rachel nodded. “All you need is a 190‑million‑year‑old fossilized rock. Blast it in a slush‑hydrogen‑engine exhaust fire, and bury it in the ice. Instant meteorite.”

“To a tourist, maybe,” Corky said, “but not to a NASA scientist! You still haven’t explained the chondrules!”

Rachel tried to recall Corky’s explanation of how chondrules formed. “You said chondrules are caused by rapid heating and cooling events in space, right?”

Corky sighed. “Chondrules form when a rock, chilled in space, suddenly becomes superheated to a partial‑melt stage‑somewhere near 1550 Celsius. Then the rock must cool again, extremely rapidly, hardening the liquid pockets into chondrules.”

Tolland studied his friend. “And this process can’t happen on earth?”

“Impossible,” Corky said. “This planet does not have the temperature variance to cause that kind of rapid shift. You’re talking here about nuclear heat and the absolute zero of space. Those extremes simply don’t exist on earth.”

Rachel considered it. “At least not naturally.”

Corky turned. “What’s that supposed to mean?”

“Why couldn’t the heating and cooling event have occurred here on earth artificially?” Rachel asked. “The rock could have been blasted by a slush‑hydrogen engine and then rapidly cooled in a cryogenic freezer.”

Corky stared. “Manufactured chondrules?”

“It’s an idea.”

“A ridiculous one,” Corky replied, flashing his meteorite sample. “Perhaps you forget? These chondrules were irrefutably dated at 190 million years.” His tone grew patronizing. “To the best of my knowledge, Ms. Sexton, 190 million years ago, nobody was running slush‑hydrogen engines and cryogenic coolers.”

Chondrules or not, Tolland thought, the evidence is piling up. He had been silent now for several minutes, deeply troubled by Rachel’s newest revelation about the fusion crust. Her hypothesis, though staggeringly bold, had opened all kinds of new doors and gotten Tolland thinking in new directions. If the fusion crust is explainable . . . what other possibilities does that present?

“You’re quiet,” Rachel said, beside him.

Tolland glanced over. For an instant, in the muted lighting of the plane, he saw a softness in Rachel’s eyes that reminded him of Celia. Shaking off the memories, he gave her a tired sigh. “Oh, I was just thinking . . .”

She smiled. “About meteorites?”

“What else?”

“Running through all the evidence, trying to figure out what’s left?”

“Something like that.”

“Any thoughts?”

“Not really. I’m troubled by how much of the data has collapsed in light of discovering that insertion shaft beneath the ice.”

“Hierarchical evidence is a house of cards,” Rachel said. “Pull out your primary assumption, and everything gets shaky. The location of the meteorite find was a primary assumption.”

I’ll say. “When I arrived at Milne, the administrator told me the meteorite had been found inside a pristine matrix of three‑hundred‑year‑old ice and was more dense than any rock found anywhere in the area, which I took as logical proof that the rock had to fall from space.”

“You and the rest of us.”

“The midrange nickel content, though persuasive, is apparently not conclusive.”

“It’s close,” Corky said nearby, apparently listening in.

“But not exact.”

Corky acquiesced with a reluctant nod.

“And,” Tolland said, “this never before seen species of space bug, though shockingly bizarre, in reality could be nothing more than a very old, deepwater crustacean.”

Rachel nodded. “And now the fusion crust . . .”

“I hate to say it,” Tolland said, glancing at Corky, “but it’s starting to feel like there’s more negative evidence than positive.”

“Science is not about hunches,” Corky said. “It’s about evidence. The chondrules in this rock are decidedly meteoric. I agree with you both that everything we’ve seen is deeply disturbing, but we cannot ignore these chondrules. The evidence in favor is conclusive, while the evidence against is circumstantial.”

Rachel frowned. “So where does that leave us?”

“Nowhere,” Corky said. “The chondrules prove we are dealing with a meteorite. The only question is why someone stuck it under the ice.”

Tolland wanted to believe his friend’s sound logic, but something just felt wrong.

“You don’t look convinced, Mike,” Corky said.

Tolland gave his friend a bewildered sigh. “I don’t know. Two out of three wasn’t bad, Corky. But we’re down to one out of three. I just feel like we’re missing something.”