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.
The Cuddlies here certainly had no premonition of what was about to happen to their faraway cousins. Attracted by the festive atmosphere, they hung around the people, popping in and out of crevices and sometimes pulling at space-suit legs to be picked up.
“You could see it now if you were hanging in a bosun’s chair over the outside rim,” Jun Davd’s voice sounded in his ear. “It’s cutting upward from below a chord drawn between you and its point of intersection. It will rise above your sunward horizon after transit.”
“How soon?” Bram asked.
“Four minutes. If you sight along the outer edge, you ought to be able to see some lightening of the limb.”
Bram strained his eyes. Beside him, Jao, fussing with the tripod of a theodolite, straightened for a look.
Yes, the precipice edge that faced the interstellar night had gained a silvery hairline illumination. It projected a short distance as a faint straight scratch against the darkness. Where the scratch ended would be the theoretical horizon.
“Got it?” he asked Jao.
Jao struggled with the theodolite. “Just a second. Yah. Here we go.”
“One minute.”
All across the pebbled plain, space-suited figures showed that they were listening in on the circuit by ceasing their activities and becoming still. The Cuddlies, sensing the humans’ absorption, froze.
“Now,” Jun Davd said.
Where the threadlike horizon narrowed to invisibility, there was a great flare. Garish light spilled over the plain, casting long black shadows. Human figures, their reflexes slower than their helmet filters, raised arms in a delayed reaction to ward off the light.
Bram saw streaks of movement through the awful glare: startled Cuddlies popping back into their holes. When his eyes adjusted, not a Cuddly was to be seen anywhere.
The light dwindled to a point and disappeared. Moments later, a bright star rose against the inward horizon.
Except that it couldn’t be a star, because it was in front of one of the great, dully visible faces of a disk.
Jun Davd’s voice in Bram’s ear was tinged with sorrow. “The exhaust swept across one of the regions we never had a chance to send a survey team to. The one with the great elliptical bowl and the pyramidal objects rising tens of miles high on stilts. Radar echoes appeared to show a small city in the vicinity to service it, whatever it was. We thought it might be a research center of some sort.”
“I remember,” Bram said.
“There’s nothing there no
w but thousands of square miles of melted slag.”
Bram thought of all the Cuddly warrens that must have lain under the complex and about all the Cuddlies outside the zone of direct destruction that would be dying of radiation sickness in the days and Tendays ahead.
Beside him, Jao swore. “I was going to come back. Maybe in a couple of hundred years when we got ourselves established and could afford to lay off a little. The pyramid installation was the first place I wanted to look at.”
In the disk-filled inner sky, the artificial star seemed to slow as if it were on a rubber band. Slowly, slowly, the rim of the diskworld pulled it back.
“They’re not going to bother to go into an orbit,” Jun Davd’s voice said. “They’re just going to hang there.”
“Disposable ship,” Jao said. “Or disposable colonists.”
“A life form that just sets blindly out and goes anywhere,” Jun Davd mused, “and takes root if it can. And now, I’m afraid, they’re making their second pass to bring them to a halt over the rim. They don’t bother to think things out in advance. They’re empirical.”
The star hung over the point of the horizon and winked out. Across the narrow plain, space-suited people eddied about, and groups began to break up. A few cautious Cuddlies popped up out of their holes.
“Show’s over,” Bram said.
Back inside a sports arena that buzzed and echoed with excited conversation, Bram and Jao conferred with Jun Davd and watched on their portable screen the images from Yggdrasil’s remote sensors.
“We were lucky,” Jun Davd’s distant voice said. “One of our orbiting cameras happened to be no more than a quarter million miles from where our visitor decided to park. We’ve moved it closer in the last hour, and we’re still closing.”
People kept poking their heads into the alcove where Bram and Jao had installed themselves. It would have been hard to jam more people into the area where people were crowding around for a look at the screen. Outside, on the rocky floor of the arena, a number of people had been foresighted enough to fetch their own personal viewscreens from their quarters and slave them to Bram’s circuit, and each of these had growing knots of watchers around it.
“They’re continuing to ignore us,” Jun Davd said. “Not a peep on any wavelength.”
Bram studied the fuzzy image. The lack of definition took away the regularities that would have labeled the ship an artificial shape and made it look like a life form. A life form with a long lumpy stem whose segments swelled where they fit into each other and a living jelly of bubbles to cap it. The nodules along the shaft fostered the notion.
For a moment Bram toyed with the idea. Yggdrasil was a living spaceship, after all. Why not this? What kind of life form would look like a budding stick, and what function would be served by the gob of bubbles at one end?
Then he dismissed the thought. The thing was a machine, after all—a relatively primitive machine that generated a howling storm of hydrogen-helium fusion and probably poisoned’ its inhabitants.
“We make it at approximately twenty miles long,” Jun Davd said. “It could alight in Yggdrasil’s branches and never be noticed, but it’s still an impressive achievement for a manufactured article.”
“What are they doing?” Bram said.
“Nothing, as far as we can tell. No extravehicle activity, no electromagnetic emissions. No attempt to reorient the axis of the ship as a preliminary to achieving some sort of rational orbit. They just appear to be waiting.”
“Waiting for what?” Jao rumbled. “They sit there like that, and eventually they’re going to drift off the rim and get sucked down the side. Then they’re going to have to turn on that torch of theirs and burn some more landscape.”
“Perhaps they don’t care,” Jun Davd said.
Bram was staring at the glob of bubbles. Overmagnification had blended them into an undifferentiated mass, but despite the bleared focus there was enough mottled shadowing for the eye to appreciate them as a clump of hundreds of separate spherules.
They were hollow, according to Jun Davd’s radar echoes. Empty fuel tanks, each a couple of thousand feet in diameter—big enough to hold millions of tons of frozen hydrogen in its different isotopic forms. And there would be a complex maze of piping to skim off the helium three as it became available and store that separately, too.
Tritium was biologically hazardous. It was hard to believe that the empty bubbles had been converted into environmental pods. Jun Davd’s imagination must have run away with him. Surely no people would be that reckless with their generations.
The vague mottling seemed to shift, showing one of the globules more distinctly.
“Do I see movement?” Bram said. “Or is that just image shimmer?”
Jao grabbed Bram’s arm. “No, it’s movement.”
As they watched, one of the bubbles detached itself from the foamlike cluster and drifted free. A fine mist spouted from it.
“Chemical jets,” Jun Davd said. “They’re matching velocity with the rim.”
A hum of voices rose in the surrounding bay. “Hold it down,” Jao thundered.
“You were right,” Bram told Jun Davd. “They moved into their empty fuel tanks. If that one held tritium, there must still be residual radiation. They’d have to be desperate for expansion room.”
“The original life-support system must have been confined to the budlike structures on the stem,” Jun Davd said. “But with the fuel tanks, they’d have a hundredfold the living space in reserve, becoming available as they spilled over.”
“What kind of intelligent race,” Bram said in dismay, “would breed that unrestrainedly, with no sureties at their destination?”
Ame pushed through the surrounding press of bodies. “The longfoots,” she said. “The females had a dozen young to a litter, remember? They’ve come back.”
“Or their successors have,” Bram said. “Whatever else the longfoots were, they were a thoughtful people. That ship doesn’t look like their technology.”
“Rise and fall, Bram-tsu,” Ame said defensively. “Devolution and reradiation of species.”
On the screen, the separated globule fell with alarming speed toward the narrow rimscape. “That’s awfully big to be using as a lander, even on a low-gravity world,” Jun Davd said. “But that’s what they’re doing with it.”
“One mistake and they’ll be scattered all over the landscape,” Jao grunted.
Bram calculated spherical volume in his head. “There could be a population of thousands in that bubble. If all of the bubbles are inhabited…”
“These strangers must like to travel in large crowds and take their environment with them,” Jun Davd said. “That detachable habitat of theirs is big enough to qualify as a self-contained colony. The ship could drop more of them off here and there around the rim and leave them to fend for themselves. Then flit around the system and seed the other disks.”
“You talk as if that ship were a living organism.”
Jun Davd laughed. “If the surviving colonies grow up to build more ships like it, then it fits the definition.”
Trist’s voice cut in. “We’re getting message traffic now between the ship and the lander.”
“Radio? Laser?” Jao’s voice was impatient.
“Neither. They communicate by modulating polarized light—switching rapidly back and forth to different planes of polarization. We can’t read the signal, but it’s a signal, all right.”
“What kind of pattern? Binary, or what?”
“No, it’s positional. It codes for some kind of grid. And now that you know that, you know as little as I do.”
“Why would they modulate polarized light?” Bram asked. “If you’re going to communicate by light, there are easier ways to modulate it for a signal.”
It was Ame, unexpectedly, who answered. “Perhaps because it corresponds to their natural sensory input.”
“Now, Ame, we use radio mostly,” Jao said condescendingly. “But we don’t see
by radio waves.”
“No,” she said, “but we use it the way we use visible light—by modulating its frequency. Or we use it by mimicking sound—by modulating the amplitude.”
Bram pondered Ame’s startling supposition. “But where does a positional grid come into it?”
“I don’t know, Bram-tsu. We use radio waves to build up pictures or sound. And when we use laser, we use it more or less as if it were just an improved kind of radio. It has something to do with the way they think or perceive things.”
“Trist, can you rig up something that’ll modulate polarized light?” Bram asked.
“Sure, nothing to it,” came Trist’s cheerful voice.
“Can you beam some of their own patterns back at them—just as a recognition signal? Just to get them to notice us.”
“I’ll get on it right away.”
“And get somebody working on that grid.”
“The chess club’s already taken it on as a project. So have the linguists.”
“Get them together.”
On the screen, the stick ship had moved out of the frame as Jun Davd’s remote camera followed the life-support module. It showed as a pale blob against a rim-scape that whizzed by at blurring speed.
“Looking for a spot to light,” Jun Davd said. “They had a choice of two directions. They chose yours.”
“How long before they get here?”
“At their present velocity? About two days.”
Two days later,’ the thing passed overhead, looking very large. Everybody was outside again for the passage. As it sailed by, everybody waved. A few energetic jumping jacks leaped straight up fifty feet or more, wigwagging with both hands. But the bubble took no notice. It receded into the distance, blank as an egg.
“They almost nicked one of the moonropes,” Jao said. “They’re flying much too close to the rim’s edge. And too low. The pilot’s a bit impetuous, isn’t he?”
Bram, sweating inside his helmet, hand-cranked the flywheel—mounted telescope to follow the enormous spheroid. The others crowded close to look at the photoplastic image in the visored plate at the end of the barrel.
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