The Ice Limit

But I didn't like rubbing elbows at faculty sherry hour, or going to conferences and chatting with rock jocks about collisional ejection and cratering mechanics. I guess the feeling was mutual. Anyway, my academic career lasted all of five years. Got denied tenure. I've been on my own ever since.'

He held his breath, thinking of his ex-partner, realizing this was a poor choice of words. But the captain did not pursue it, and the moment passed.

'All I know about meteorites is that they're rocks that fall out of the sky,' Britton said. 'Where do they come from? Other than Mars, of course.'

'Martian meteorites are extremely rare. Most of them are chunks of rock from the inner asteroid belt. Small bits and pieces from planets that broke up soon after the formation of the solar system.'

'The thing you're after isn't exactly small.'

'Well, most of them are small. But it doesn't take a whole lot to make a big impact. The Tunguska meteorite, which hit Siberia in 1908, had an impact energy equal to a ten-megaton hydrogen bomb.'

'Ten megatons?'

'And that's small potatoes. Some meteoroids hit the earth with a kinetic energy greater than one hundred million megatons. That's the kind of blast that tends to end an entire geologic age, kill off the dinosaurs, and generally ruin everybody's day.'

'Jesus.' Britton shook her head.

He laughed dryly. 'Don't worry. They're pretty rare. One every hundred million years.'

They had worked their way through another maze of corridors. McFarlane felt hopelessly lost.

'Are all meteorites the same?'

'No, no. But most of the ones that hit the earth are ordinary chondrites.'

'Chondrites?'

'Basically, old gray stones. Pretty boring.' McFarlane hesitated. 'There are the nickel-iron types — probably like the one we're snagging. But the most interesting type is called CI chondrites.' He stopped.

Britton glanced over at him.

'It's hard to explain. It might be boring for you.' McFarlane remembered, more than once, putting a glaze over everyone's eyes at a dinner party in his younger, enthusiastic, innocent years.

'I'm the one that studied celestial navigation. Try me.' 'Well, CI chondrites are clumped directly out of the pure, unadulterated dust cloud the solar system formed from. Which makes them very interesting. They contain clues to how the solar system formed. They're also very old. Older than the Earth.'

'And how old is that?'

'Four and a half billion years.' He noticed a genuine interest shining in her eyes.

'Amazing.'

'And it's been theorized that there's a type of meteorite even more incredible —'

McFarlane fell silent abruptly, checking himself. He did not want the old obsession to return; not now. He walked on in the sudden stillness, aware of Britton's curious gaze.

The corridor ended in a dogged hatch. Undogging the cleats, Britton pulled it open. A wall of sound flew out at them: the huge roar of endless horsepower. McFarlane followed the captain out onto a narrow catwalk. About fifty feet below, he could see two enormous turbines roaring in tandem. The huge space seemed completely deserted; apparently it, too, was run by computer. He gripped a metal pole for support, and it vibrated wildly in his hand.

Britton looked at him with a small smile as they continued along the catwalk. 'The Rolvaag is driven by steam boilers, not diesel motors like other ships,' she said, raising her voice over the roar. 'We do have an emergency diesel for electricity, though. On a modern ship like this, you can't afford to lose power. Because if you do, you've got nothing: no computers, no navigation, no fire-fighting equipment. You're a drifting hulk. We call it DIW: dead in the water.'

They passed through another heavy door at the forward end of the engine space. Britton dogged it shut, then led the way down a hallway that ended at a closed elevator door. McFarlane followed, grateful for the quiet.

The captain stopped at the elevator, looking back at him calculatingly. Suddenly, he realized she had more on her mind than a tour of the jolly old Rolvaag.

'Mr. Glinn gave a good talk,' Britton said at last.

'I'm glad you think so.'

'Crews can be a superstitious lot, you know. It's amazing how fast rumor and speculation can turn into fact belowdecks. I think that talk went a long way toward squelching any rumors.' There was another brief pause. Then she spoke again.

'I have the feeling Mr. Glinn knows a lot more than he said. Actually, no — that isn't the right way to put it. I think maybe he knows less than he let on.' She glanced sidelong at McFarlane. 'Isn't that right?'

McFarlane hesitated. He didn't know what Lloyd or Glinn had told the captain — or, more to the point, what they had withheld. Nevertheless, he felt that the more she knew, the better off the ship would be. He felt a sense of kinship with her. They'd both made big mistakes. They'd both been dragged behind the motorcycle of life a little longer than the average Joe. In his gut, he trusted Sally Britton.

'You're right,' he said. 'The truth is, we know almost nothing about it. We don't know how something so large could have survived impact. We don't know why it hasn't rusted away. What little electromagnetic and gravitational data we have about the rock seem contradictory, even impossible.'

'I see,' said Britton. She looked into McFarlane's eyes. 'Is it dangerous?'

'There is no reason to think so.' He hesitated. 'No reason to think not, either.'

There was a pause.

'What I mean is, will it pose a hazard to my ship or my crew?'

McFarlane chewed his lip, wondering how to answer. 'A hazard? It's heavy as hell. It'll be tricky to maneuver. But once it's safely secured in its cradle, I have to believe it'll be less dangerous than a hold full of inflammable oil.' He looked at her. 'And Glinn seems to be a man who never takes chances.'

For a moment, Britton thought about this. Then she nodded. 'That was my take on him, too: cautious to a fault.' She pressed the button for the elevator. 'That's the kind of person I like on board. Because the next time I end up on a reef, I'm going down with the ship.'

Rolvaag,

July 3, 2:15 P.M.

AS THE good ship Rolvaag crossed the equator, with the coast of Brazil and the mouth of the Amazon far to the west, a time-honored ritual began on the ship's bow, as it had on oceangoing vessels for hundreds of years.

Thirty feet below deck and almost nine hundred feet aft, Dr. Patrick Brambell was unpacking his last box of books. For almost every year of his working life he had crossed the line at least once, and he found the concomitant ceremonies — the 'Neptune's tea' made from boiled socks, the gauntlet of fish-wielding deckhands, the vulgar laughter of the shellbacks — distasteful in the extreme.

He had been unpacking and arranging his extensive library ever since the Rolvaag left port. It was a task he enjoyed almost as much as reading the books themselves, and he never allowed himself to hurry. Now he ran a scalpel along the final seam of packing tape, pulled back the cardboard flaps, and looked inside. With loving fingers, he removed the topmost book, Burton's Anatomy of Melancholy, and caressed its fine half-leather cover before placing it on the last free shelf in his cabin. Orlando Furioso came next, then Huysmans's A rebours, Coleridge's lectures on Shakespeare, Dr. Johnson's Rambler essays, Newman's Apologia pro Vita Sua. None of the books was about medicine; in fact, of the thousand- odd eclectic books in Brambell's traveling library, only a dozen or so could be considered professional references — and those he segregated in his medical suite, to remove the vocational stain from his cherished library. For Dr. Brambell was first a reader, and second a doctor.

The box empty at last, Brambell sighed in mingled satisfaction and regret and stepped back to survey the ranks of books standing in neat rows on every surface and shelf. As he did so, there was the clatter of a distant