“Divided by three, yes,” she said.
Around them on the booty-littered plain, people were gathering into groups, pointing excitedly at the sky. Bram knew that if he switched to the general frequency he would hear a babble of voices. A delegation of about a dozen people, spotting Jun Davd’s tall space-suited figure and his own well-worn tabard, were bouncing across the fiat ribbonscape toward them.
“Who?” Bram said. “Relatives of the Cuddlies? The collateral branch you postulated that might have evolved from the same root stock after the longfoots carried the Cuddlies here?”
“No,” Ame said. “That would have been the last cycle—twenty-six million years ago. The proto-Cuddlies missed their chance. They never traveled to the stars.”
Bram stared at the blue spark that was heading toward them. “Who then?” he said.
“We’ll know very soon,” Jun Davd said.
CHAPTER 9
The alien ship resembled a long jointed stick studded with budlike structures and a cluster of bubbles like white foam at one end. It was very large, as starships must be. It was not worldlike in Yggdrasil’s sense, but the segmented shaft was many miles long, and each individual bubble was easily a half mile in diameter.
“It’s a fusion vessel, all right, but not a ramjet,” said Jun Davd’s deep, composed voice from the screen. “They carried their fuel with them. They’re using a deuterium-helium three reaction. But there are traces of tritium from previous burns.”
Bram saw the implications immediately. “They started their trip with a deuterium-tritium reaction. And they’ve been at it long enough to have to switch fuels because of the decay of their tritium.”
He turned his eyes from the sticklike image on the portable viewscreen long enough to exchange glances with Jao. Jun Davd had returned to the tree in order to have the full resources of the observatory at his disposal, but the burly physicist had left Trist to hold the fort and returned to the diskworld, where, he said, “the action’s going to be.”
The strangers’ starship had been decelerating steadily for six days now at half a g. It had covered more than two hundred million miles since it had first been spotted approaching from the outer system. It would rendezvous with the diskworld in only a few hours—still with too much velocity, according to Trist.
Bram, waiting with Jao, had set up shop in the great sports arena, which was mostly cleared out now. A few people in casual dress moved through the empty spaces, picking over the remaining exhibits. Ame was among them, a distant figure working with a male associate to pack and label pods. Bram had sent all the junketing tourists—and everybody else who could be spared—back to the tree. He didn’t want half the population milling around where they could not easily be rounded up. Not with this new development unfolding. But Ame had refused to go. “Not on your life,” she’d said. “I wouldn’t miss this for anything. Besides, you’re going to need me, and Jorv, and all the other experts on terrestrial life.” She was right, Bram knew. Only a few hundred people remained on the diskworld, but he had seen to it that a sprinkling of specialists in the once-abstract disciplines was included.
“Yes,” Jun Davd’s voice agreed. “If they came from Sol, they’ve been traveling at nonrelativistic speeds. Tritium’s half-life is only twelve years and a bit. At the end of their first fifty or sixty years, most of it would have turned into helium three, their secondary fuel. And what does that suggest?”
Jao’s eyes glinted. “Deuterium-tritium fusion is easy. But tritium’s hard to come by. They would’ve made it back home as a by-product of their fusion reactors. Deuterium-helium three fusion’s easy, too—but first you have to accumulate enough helium three. Deuterium’s more plentiful. But I guess they’re not capable of deuterium-deuterium fusion yet. Nor of the boron fusion-fission reaction the Nar used in their early starships.”
He glanced at the bubble-and-stick image that was being transmitted from Yggdrasil’s telescopes. “So this is a very early model starship. They’re in the first stages of exploration.”
“It isn’t an exploration ship. It’s a colony ship. They don’t have enough reaction mass for a return trip.”
“But the bubbles…”
“If they ever were fuel tanks, they’re empty now. Our radar shows they’re hollow. And they haven’t collapsed, as a sensible membrane envelope would, nor have they been cast off. I suspect that they’ve been converted into environmental pods for a very rapidly expanding population.”
“They could have planned to set up reactors here to manufacture tritium,” Bram suggested. “Or mine a gas giant for helium three.”
“Except that there are no gas giants in this system. Nor oceans to extract deuterium from. All they could have known about this system is that there was mass here. And energy.”
Jao was agape, and Bram didn’t blame him. “You mean they sent a shipload of colonists out—to travel for generations and breed aboard ship—without knowing for sure what they’d find here? They must hold their lives cheap!”
“And it must follow that they hold other lives cheap, as well,” Jun Davd said hollowly.
“Jun David, what are you driving at?” Bram demanded.
“They’re closing with the disk very rapidly, and they still haven’t turned off their fusion drive. They must have seen Yggdrasil. And felt our radar probing them. They know there’s life here.”
Trist’s voice cut in, sounding harsh. “They’re going to overshoot, Bram. They’ll have to cut right across the rim of the diskworld.”
Bram was aghast. “They’d have to assume there must be intelligent life on the surface even if they didn’t care about the artifacts they’d be destroying. And they have no way of knowing exactly where on the rim we might be.”
“We’re sending them radio messages,” Trist said. “Just intelligent noises on every wavelength—number patterns and so forth. They don’t respond. It’s as if we don’t exist for them.”
“I can evacuate,” Bram said, thinking frantically. “No, that would take too long,’ wouldn’t it, with everybody spread out? It wouldn’t matter, anyway. Yggdrasil’s less than twenty thousand miles away, right in the path of destruction if the drive exhaust comes anywhere near here.”
“Yggdrasil’s safe, and so are you, we think,” Jun Davd said. “These careless strangers will intersect the rim between moons—at least five or ten million miles from your position.”
“You think,” Jao growled.
A scattered crowd had gathered on the plain, facing the point where the long straight ribbon of land vanished into infinity. About three hundred people were left on the diskworld, and virtually all of them were here in their space suits. They stood in small, chatting groups or lounged against the landing legs of the waiting shuttles. A few enterprising souls had even climbed to perches atop the spaces vehicles for a better view.
Bram was still uneasy about everybody being out in the open. His first instinct had been to keep people as far underground as possible. But Jun Davd had assured him that the alien ship was holding its course. For all practical purposes, the enormous curvature of the rim was a straight line, and even if that dreadful inferno of fusing deuterium and hydrogen three passed only marginally below the theoretical horizon, millions of miles of diskworld would be interposed between Bram’s people and death.
Not so for the Cuddlies inhabiting that distant latitude. Bram’s mouth tightened into a grim line as he thought of the slaughter that would take place in a few minutes.