The Jupiter Theft

From less than a quarter million miles away, the alien ship showed its form starkly through the telescopes. It swam against the luminous striations of Jupiter, an angular, many-armed silhouette. The shape was peculiar. It wasn’t designed the way humans would have done it, but it made sense.

Picture a slender rod fifteen miles long—slender only by virtue of its enormous scale. It had to be at least three miles in thickness. Radar echoes had shown its cross section to be an equilateral triangle—a three-sided stick. The echoes also must have told the aliens that someone was looking at them.

From the tip of the rod, three long arms sprouted sideways making the shape of a Y. Each of the arms was fifteen miles long. Folded back along the rod, they would just about have reached its opposite end.

Each arm ended in a prism. The cross section of the prisms was the same as the rod—an equilateral triangle three miles on a side. They were in effect shorter slices of the rod, measuring four and a half miles from triangular face to triangular face. The arms with their clubbed ends twirled lazily, a whirligig for titans.

There were five of the great ships, clustered in a pentagonal formation, revolving around a common center of gravity. But this one, etched against Jupiter’s roiling clouds, was easiest to see.

Jameson tore himself away from the eyepiece reluctantly and levered himself across the observatory to join the rest of the group. They were gathered around a large projection screen which reproduced the telescope image, but it wasn’t quite the same as seeing it firsthand.

“It’s obvious,” Pierce was saying. The young astronomer was flushed with excitement, talking too rapidly. “The long shaft is their drive section. In flight, those three arms fold back along the shaft like the ribs of an umbrella. Those nice flat surfaces are meant to rest against the three faces of the shaft.”

He stopped, out of breath, and glanced apologetically at Ruiz.

“Go on,” Ruiz said. “You’re doing fine.”

Pierce ran a hand over his mussed hair. “But when they’re not accelerating or decelerating,” he said, “the arms open out and spin to give them artificial gravity. Those wedge-shaped modules at the ends of the arms are the environmental pods.”

“Environmental pods!” Chu exclaimed. He sucked on his wispy moustache. “Look at the size of them! They’re—they’re worldlets!”

“To think of engineering on such a scale!” Li said admiringly. “Supporting masses like that on ten-mile booms!” He flashed a disingenuous smile in Jameson’s direction and said, piously: “They must be socialists.

That earned him a suspicious stare from Tu Juechen. She sucked in her pleated cheeks and fixed him with her little monkey eyes. Li met her gaze innocently. The Struggle Group leader had shown up shortly after Jameson and Li had arrived and had been glaring at everybody since then, poor Dr. Chu most of all.

Jameson couldn’t imagine why she was there. It wasn’t any sort of formal meeting. Ruiz had called him up when he was turning the bridge over to Kay Thorwald, and asked him if he’d like to drop by for a look at the alien ships before he went back to the spin section. The ships had just emerged from behind Jupiter in the complicated sixteen-day orbit they shared with the Cygnus Object’s former moon, and Ruiz had promised him a more spectacular view than last time. On the way back to the observatory he’d bumped into Li, who’d immediately asked if he could tag along.

Jameson got Li off the hook by quickly saying, “Djen hwa. As you say, the engineering’s on a tremendous scale. Besides swiveling the asteroid-size modules outward on the ends of those booms, they’ve got to manipulate them so that they’re turned around.”

“Yes, yes, of course!” Pierce cried. “My God, I didn’t think of that!”

Tu Jue-chen looked from one to the other of them, a simian frown creasing her brow. “I do not understand,” she said.

“What tongzhi Jameson means,” Dr. Chu said hastily, “is that the pods must be reversed when the arms are rotating. Otherwise the centripetal force that substitutes for gravity would be in the wrong direction. The pods would be ‘upside down.’ ”

“You’re assuming that the booms are attached at the rear of the drive section?” Ruiz said.

Chu gave a little bow. “Of course. The three arms would fold forward, to put the environmental pods as far away from the drive as possible. Fifteen miles away from it, in fact. We do not know what energies these creatures must command to travel at nearly the speed of light, but we can assume that they are dangerous.”

“And,” Pierce interrupted breathlessly, “when the arms are extended, the pods are still fifteen miles from the drive—at right angles, of course. In case there’s any danger from lingering radiation, I suppose.”

“Yes, yes,” Chu said, looking annoyed. “The point is, when they’re accelerating, or turned around to decelerate, their artificial gravity is in the direction of their line of flight. Otherwise, they get it from spin, just as we do.”

“Which proves,” Ruiz said, “that if such a thing as true ‘artificial gravity’ is possible, the aliens haven’t discovered it.”

“But they’re so far in advance of us—” Pierce began.

“Are they?” Ruiz said. “They do things on a larger scale. That’s all we know so far.”

“That’s putting it mildly,” Jameson said. “Moving whole worlds about! Building a fleet of ships larger than the Martian moons…”

Ruiz looked pensive. “Maybe there’s no other way to do it. When you’re traveling between the stars, you don’t go home again. Not after ten thousand years. You take your whole society with you?”

Interest flickered in Tu Jue-chen’s close-set little eyes. “How many of these creatures do you suppose there are aboard those vessels?” she asked.

Ruiz nodded at Pierce. “Do you want to take a crack at it?”

“Hmm. Let’s assume that they’re roughly our size. Somewhere between twice our size and half our size. There must be an optimum size range for intelligent life. Much smaller than that and they don’t pack enough brain tissue. Much larger and they become unwieldy. Specialized—”

“There are whales,” Li said mischievously. “And elephants.”

Pierce looked disconcerted. “Hmm, yes. But I can’t see a gigantic sea creature developing into a space traveler, no matter how intelligent. The early steps would be too difficult. Besides, it’s hard to imagine those pods as giant aquaria, sloshing around with liquid. The amount of mass involved, for one thing—”

“But very large land animals,” Li pressed him. “From low-gravity planet. Space travel would be easy in early stages. And pods are rotating very slowly. At one third gravity, is it not correct?”

Maybury had joined the group unobtrusively, her arms full of stacked photographic plates. “But when the Cygnus Object was approaching the solar system, Dr. Ruiz noticed that it was braking at nine hundred and eighty centimeters per second per second,” she said gravely. “Approximately one g for a sustained period of time. Perhaps they spin their ships at less than normal g-force for the same reasons we do.”

Pierce nodded gratefully. “Yes, yes,” he said. “We’re getting away from the subject. We can assume anything we like, but for the sake of convenience, let’s assume that they’re in a normal size range for highly evolved terrestrial animals.—”

“How many creatures?” Tu Jue-chen said tartly.

“Yes, I’m getting to that,” Pierce said. “Let me see if I remember my geometry. At three miles to a side, an equilateral triangle would have an area of approximately four and a half square miles. Now, how many levels in one of those pods? Let’s be conservative and assume fifty-foot ceilings. Room for an ecology, with the equivalent of trees and so forth. That gives more than one hundred levels per mile of height…”

“One hundred and five,” Chu said pedantically. “And six tenths.”

“Yes … I mean, shih,” Pierce said, flustered. He floundered a moment and went on. “Now, I’m going to be conservative again and assume the same volumetrics as our own ship. That is to say, the Cygnans occupy only the lower three miles of their pods, and leave the top third for storage, machinery, space- intensive hydroponics, and so forth. That gives us three hundred—”

“Three hundred and sixteen point eight,” Dr. Chu said severely.

“—levels, each with an area of four and a half square miles. That works out to…” he floundered again.

“One thousand four hundred and twenty-five square miles per pod,” Maybury supplied. She looked straight at Chu. “And point six,” she added.