He looked at her blankly. "Dumb animals? Now, Liz..."

"It's a stupid pun. A Latin proverb:Dum anima est, spes esse ... while there's life, there's hope."

Abruptly she burst into tears and walked away.

Boyle was climbing down the gray steps toward him, Kay, and the two Chinese following. They had Klein and Chia Lan-ying, the Chinese stores exec, in tow.

"Here's your two porters, Commander," Boyle said. "You'd better get moving."

Jameson looked doubtfully at Chia Lan-ying. She was a lovely thing, with rosy cheeks and huge eyes almost hidden by dense bangs. She looked tiny and frail next to Klein.

"Maybe you'd want to send comrade Yeh or one of the men," he said. "We want to move stuff as fast as possible."

Tu Jue-chen drew her simian brow into a network of angry V's and said, "You will not fool me.

Comrade Chia is in charge of supplies."

Jameson sighed and gave it up.

Chia proved to be a deft and efficient worker, darting through the moldering piles of goods and finding useful items and helping Klein and Jameson load them on the circular dolly with three ball-bearing wheels that the Cygnans had provided. Jameson had to admit that she was a better choice than Yeh; muscles weren't that important in the low gravity anyway.

Klein tried his patience, though. He kept goofing off to prowl through the scattered stuff from the cabins when he was supposed to be helping Jameson wrestle the heavy stuff like food lockers and fish tanks onto the dolly. Jameson was about to say something when he saw Klein stiffen, then pounce on something in one of the jumbled piles.

"My duffle," he said sullenly when Jameson came up behind him. "And some of my other stuff."

"Show it to the Cygnans before you load it," Jameson said. He wasn't going to make an issue about Klein's personal possessions; maybe the man would get down to work now that he had found them. "We can't take a chance on trying to sneak contraband past them."

He'd already caught Klein attempting to pocket somebody's jackknife. The Cygnans frowned on anything that might be used as a weapon, though Jameson had gained a dispensation for safety razors when he explained their use.

"Just some clothes and toilet articles," Klein said, his sallow face closed.

Jameson saw brushes, a shaving kit, Klein's heavy gum-soled boots, some crumpled garments, a pocket chess set, some fancy bottles. He gestured at a silver flask.

"All the liquor goes into the common store," he said.

"Just aftershave lotion," Klein said. He unscrewed the cap. "Here, take a sniff."

"That's not necessary," Jameson began, but Klein was already holding the flask under his nose. "Okay, come on, let's get those blankets loaded."

A cheer went up every time they pushed a loaded dolly through the gate. There were lots of willing hands to help them unload and send them back again. They worked steadily for almost two hours before the Cygnans put a stop to it.

Visiting hours were about to begin.

There was a celebration that night after the sky went dark and the observation tubes had emptied of their flitting six-legged shapes. Boyle and Hsieh had agreed that some of the liquor and joints could be doled out for a party. They could hardly have stopped it. A boost in morale was badly needed.

Jameson sat with his back against a slab of terrace, his belly comfortably full of the meal Liz Becque and the Chinese nutritionist had served up from the precious store of packaged foodstuffs he'd brought back.

It had been a brilliant approximation of aman han feast, complete with green noodles pressed from Cygnan mash. There had been reconst.i.tuted beer and wine, and a joint for every five people, and there was a great tub of punch contrived from fruit-juice concentrates and five squandered gallons of grain alcohol. It would be back to synthetic rations tomorrow, Jameson knew, but for now everybody was happy.

Maggie's head stirred on his shoulder. "Look at them," she said lazily. "I wonder if they'd be having such a good time if they knew the Cygnans were going to start moving Jupiter in six days."

Jameson looked around uneasily, but n.o.body was within earshot.

"I know," Maggie said. "It's our guilty little secret."

"Let 'em be happy while they can," he said, squeezing her hand.

In the dilute silver light, the great terraced bowl of the enclosure had lost its drabness. He could see the pale outlined figures standing around or sprawled in conversational groups, Chinese and Americans mingling. Over by the bar, a tank cover on trestles, Liz and Chia were ladling out the punch. Behind a subdued babble of voices there was the dreadful wail of a harmonica and the easy accompaniment of the guitar he'd managed to bring back for Mike Berry. Across, on the upper slope, he saw an unsteady couple heading toward a makeshift pup tent devised from a sheet and cordage, early as it still was. A number of such improvised privacy screens had been set up throughout the enclosure since they had brought back bedding.

Ruiz was holding forth a couple of levels down. He'd been giving an informal briefing to Boyle and Hsieh of what he'd deduced since Jameson had found him a lightpad with stored mathematical tables and astronomical data. A small crowd had grown around him. It now numbered about twenty.

"Hi, Tod, can you come over here for a minute?" They were waving for him.

Jameson groaned and got to his feet. He'd been through it all a dozen times already.

"Give the man a drink." Somebody put a cup of warm beer into his hand. There was a friendly thump on his back as he pushed his way through the crowd, dragging Maggie.

"Is Dr. Ruiz kidding, Tod? Is this really what those walking worms showed you?"

Ruiz's lightpad was pa.s.sed hand to hand until it reached Jameson. A glowing blue diagram had been scratched on its obsidian surface.

Jameson studied the sketch. At the center was a circle with a narrow ellipse around it, like a sketch of Saturn and its rings seen almost head on. It was the Jovian planet at the center of the Cygnans' travel arrangements, with a representation of the orbit of the robot probe that siphoned off hydrogen and turned it into kinetic energy. The Jovian's battle-scarred moon was sketched in directly above the Jovian-probe system. Ruiz had drawn a lopsided circle to indicate its...o...b..t. Below the moon, between the moon and the Jovian, was a circle of five small dots representing the Cygnan s.p.a.ceships rotating aroundtheir common center of gravity. Their common orbit around, the moon was indicated by an oval outline.

"That's about it," he said.

"Run through it again, Doc," somebody said.

"All right," Ruiz said good-naturedly. "Hold that up, Commander, so everybody can see. First we have the robot in a powered orbit around the gas giant. It's traveling at very nearly the speed of light, using up the planet's ma.s.s without having to accelerate it, until its own Einsteinian ma.s.s outweighs what's left of the planet."

"Wait a minute, Doc!" a boisterous voice said. "The centrifugal force would be tremendous!"

"You weren't listening, Gifford. I said apowered orbit."

"Yeah, but did you figure out the centrifugal force?"

"It doesn't matter," Ruiz said with rare patience. "Whateverpercentage of the total kinetic energy is needed to maintain a tight circle is progressively diverted to a thrust perpendicular to the orbit. The Cygnans aren't concerned with efficiency. They've got a whole planet to use up. By the same token, a percentage of the total kinetic energy is used to provide a vector, so the Cygnans can get the whole system moving in whatever direction they want."

Mike Berry had stopped playing the guitar and had moved into the circle. "That's right," he said. "All it means is that the Cygnans strip their Jovian gas tank of ma.s.s faster-or longer-before they can move what's left."

"Yeah," somebody gibed. "Shut up, Giff!"

Ruiz straightened creakily. Like most of the others, he was wearing one of the crisp new uniforms Jameson had retrieved that morning, but it hung loosely on his emaciated frame.

"If we've got that settled," Ruiz said, "would you flip the store-and-recall b.u.t.ton for us, Commander?

Keep doing it. Thank you."

Jameson watched the pictures change on the black surface. Ruiz had painstakingly drawn a four-step animated diagram showing the multiple orbits. The moon jumped in its circle around the Jovian planet, moving counterclockwise. The rosette of dots jumped in its egg-shaped orbit around the moon, moving clockwise.

"The orbit of the ships around the moon has the same period as the moon's...o...b..t around the planet," Ruiz went on. "Doubtless the ships' orbits are continuously adjusted to keep them synchronized as the planet shrinks and the moon's...o...b..t changes. But as you can see, the ships arealways sheltered from the radiation caused by collision with interstellar hydrogen."

"Beautiful, beautiful," Mike murmured.

"Commander Jameson thinks-and I agree with him-that a significant portion of that impacting hydrogen also becomes grist for the Cygnans' mill. After all, it's already been ionized. It becomes an energy bonus to partially offset the inefficiency inherent in the Cygnan method of travel."

"Can I quit?" Jameson said. "My thumb's getting tired." He pa.s.sed the lightpad back to Ruiz.

"It seems kinda complicated," the Giff said, being a bad boy again.

"It wasn't complicated for the Cygnans," Ruiz said. "Don't forget, they started with the components of the system already in place. That moon they use for a shield was the world they evolved on... I wonder how they feel about traveling with its corpse. The gas giant they used for fuel was the primary that their world revolved around. It would have been natural for them to start building their fleet in orbit around their world. They had a whole population to transfer, a shipboard ecology to establish, a technology to develop. It might have taken millennia. They had the time. Perhaps they didn't develop the technology for that Einsteinian siphon of theirs until the work was well under way. They might not have traveled at relativistic speeds for the first few centuries, while they completed the shakedown for those synchronized orbits. It wouldn't have happened all at once."

Jameson was the first to pick up on it. "You said... they had the time. What do you mean?"

Ruiz was fiddling with his lightpad. He had more of his day's work stored there. He looked up, almost absently.

"One of their suns was going to go supernova. And they had half a million years to get ready for it."

The crowd around Ruiz had grown. Word had gotten about that something lively was going on. Jameson could see Liz Becque nestled against Omar, her arm around his thick waist, her post at the punchbowl deserted. Even Klein had joined the group. He was at the fringes of the crowd, his knotted arms folded, standing next to Yeh and Chia, so intent on the discussion that he'd forgotten his aversion to his Chinese shipmates.

"The Cygnans are the children of a binary system that now consists of a black hole and a blue supergiant," Ruiz said. "They spent twenty thousand years watching one of their suns swallow the other."

Beside Ruiz, Captain Boyle nodded gravely. "We can begin to understand something about the Cygnans'

motives now. We knew that they came from thedirection of the X-ray source known as Cygnus X-l, about ten thousand light-years away. What Commander Jameson managed to see on the Cygnan computer display confirmed that it was theirorigin , incredible as that seems."

Mike Berry was itchy with questions. "Twenty thousand years. That's longer than all of human history.

You sure of that figure?"

Ruiz swung his narrow beak toward him. "We can calculate the timetable for the evolution of an X-ray binary system from the ma.s.s of its components. And we get that from their dynamical behavior."

Jameson spoke up. "The Cygnan commentary got eloquent about a 'Great Mother' that swallows her...

not 'children'... maybe something like 'little brother.' I a.s.sumed it had something to do with eclipses in a double-star system. I saw some spectacular ones."

"It was more literal than that," Ruiz said. "One of their sunswas swallowing the other. And the ma.s.s exchange took place fast enough to be noticeable over the generations. It must have been a key part of the Cygnan race consciousness since they first crawled out of the ooze and became civilized beings."

Liz Becque, shuddered and drew closer to Omar. "You mean they actually would haveseen one of their suns getting bigger and the other getting smaller?"

"As their suns evolved, yes."

"Think of it!" Dmitri blurted. "To live under such a sky! When you think of the burden of myth and theology we humans have invented from our own simple sunrises and sunsets and seasons..."

"The myths would have turned into scientific knowledge," Ruiz said dryly. "When they got to the point where they knew what we know about close binaries and ma.s.s exchange, they would have known exactly what the fate of their suns would be. And exactly when it would happen."

Dmitri sucked in his breath. "A race spending its entire history with the foreknowledge of doom-first as myth, then as certain knowledge."

Jameson squeezed Maggie's hand for comfort. It was no wonder that the Cygnans had no empathy left over for other life forms.

Out of a babble of voices, someone asked: "The black hole swallows the supergiant, is that it?"

"No," Ruiz said. "It's the other way around-at first. And they hadn't got to be a black hole and a blue supergiant yet. You start with two ordinary, healthy stars. But they're big. That's important. One is about twenty solar ma.s.ses, the other about six."

He sketched two circles in the air. Such was the force of Ruiz's personality that Jameson could imagine that he saw them hanging there.

"They're in a close binary system. Very close. They circle each other in only four and a half days. There's a gas giant farther out, in their common ecosphere." He sketched another imaginary circle. "It's many times bigger than Jupiter, but not quite big enough to have been kindled into a star. It's got its own family of satellites. One of them's the Cygnan home world. It's about the size of Mercury."

"The smaller of the two bodies now in orbit around Jupiter!" Maggie said brightly.

Ruiz gave her a hooded look. "It's very likely," he said. "They had to kill their world to escape a murderous sun. I wouldn't be surprised if they had a sentimental attachment to the coffin."

"Wait a minute," Mike Berry objected. "The Cygnans boosted at one gravity. Doesn't that imply that they evolved on an Earth-size planet?"

Unexpectedly, it was Dmitri who came to Ruiz's rescue. "Takes only a year to boost up or down from light speed at one g," he pointed out. "The Cygnans could take that easily, with their body structure-six legs, low profile, no rigid bones. Besides, they're spinning this ship at one third g now."

Ruiz inclined his head in acknowledgment.

"You were telling us about the timetable for the evolution of an X-ray binary system," Jameson prompted.

"Just so," Ruiz said. "All right. We start with two healthy stars. Big stars burn out quicker. Right? So the twenty-sol star uses up its hydrogen first. It becomes a supergiant, hundreds of times larger than our own Sun. It's a helium star now..."

"Without wiping out all life in the system, Cygnans included?" Gifford said incredulously.

"It's part of a close binary system," Ruiz said. "It can only expand to the limits of its Roche lobe."

"That's why the big star looked pear-shaped!" Jameson said.

"Correct, Commander. When the star overflows its Roche lobe, the surplus ma.s.s is transferred to the companion star. The ma.s.s exchange takes only about twenty thousand years. Perhaps less. When it's finished, the twenty-sol star is down to less than six solar ma.s.ses. The six-sol star has grown to somewhat more than twenty. It adds up to about the same."

"So their joint ecosphere isn't affected," Dmitri put in. "The Cygnans survive."

"They survive, yes," Ruiz said. "But they'd have had a difficult twenty thousand years. Helium stars burn hot . The Cygnans must already have started thinking about moving from the neighborhood. They knew that worse was to come."

"The supernova?"

"Yes. The star that ate its companion's ma.s.s is in good shape. It has a new lease on life. It can burn its stolen hydrogen for another six million years. But the other star is doomed. It can burn its helium only for about half a million years. Then the carbon core explodes."

"So the Cygnans had half a million years' warning?" Mike Berry said.

"That's right. But evidently they didn't wait around that long. It's not very healthy to be in the vicinity of a supernova. From what Commander Jameson observed, it looks as if the Cygnans mobilized their society and got out within the first few thousand years."

Dmitri was trembling with excitement. "But Jamesonsaw the supernova explosion! The Cygnans left a few thousand years after the ma.s.s exchange, then kept a watch on the stars they'd left."

"Correct, Mr. Galkin." Ruiz looked as if he was enjoying himself.

"But-but that means that the Cygnans have been evolving in an artificial environment forhalf a million years! "

There was a rush of excited voices. Ruiz waited it out. He held up a hand, and the noise died down.