of artificial worldlets traveled through space! He’d hit the jackpot again. He didn’t need any math to grasp the basics of what was being shown to him.
At the center was a glowing red ball, moving against an abstract background of stars. That was the gas giant. The one they had already used up, soon to be replaced by Jupiter. Around its waist was a string of tiny chips that pulsed in sequence to indicate motion. An abstraction of the robot probe, tailored to Cygnan perceptions. He squinted more closely. On one of the three screens he could see a fan of light directed outward—the lethal spray of radiation.
Enclosing the two-body system in a wider, polar orbit was a smaller sphere of opalescent gray. One of the gas giant’s moons, dragged along by its kidnapped parent. It rotated in a plane that was almost vertical to the loop described by the probe. It put Jameson in mind of a gyroscope configuration, or perhaps one of the simplified representations of an atom that used to be popular in his schoolboy days. Then, in orbit around the moon—again in another plane—he saw five glittering mites, three-armed asterisks spinning on stems. The Cygnan ships.
The ships, in turn, were rotating around a common center of gravity, chasing one another around in a circle. It was the system of five ships, considered as a single body, that rotated around the moon.
It was beautiful.
He sat watching the show, transfixed, like a boy mesmerized by a complicated set of electric trains. Everything had its own motion. Nothing collided.
He watched it for a long time to be sure how it meshed.
To keep from being flung into space, the little probe, that-which-pulls, had to keep blowing off energy all the time the intricate procession was traveling, even when it had stopped accelerating. It was a worm, draining away the substance of the planet. There could be no such thing as coasting without consuming fuel.
The Cygnans would have to drop in periodically on star systems close to their line of flight to refuel. Otherwise they would find themselves without enough mass to brake and be doomed to go flying forever through the universe.
How many stars had they plundered of gas giants during their long hegira?
Each shanghaied planet, of course, would have cost the Cygnans at least a year’s braking time, plus another year to boost up to relativistic speeds again. For the rest of it, how long would it have taken, ship’s time, to travel the 10,000 light-years that Ruiz had postulated? At 98 percent of the speed of light, Jameson knew, the time- dilation effect would be approximately fivefold. The Cygnans had been cooped up in their triangular cans for more than two thousand years of subjective time. They had managed to maintain a technological civilization, but he guessed things were getting a little stale.
Triad was tootling at him. “Does Jameson see how we are always in the shadow of the moon?”
Jameson returned his attention to the screens. He tried to keep track of the separate motions.
The pilfered moon, despite appearances, wasn’t revolving around its parent. It was orbiting around the common center of gravity shared by the gas giant and the probe that was in tight orbit around it. But since the center of gravity was so close to the planet’s surface, of course, it made no practical difference to what he was seeing.
The moon, from his point of view above the system, was rotating counterclockwise around the gas planet. The direction of motion of the whole system was upward, toward twelve o’clock. The mitelike ships, in orbit around the moon, were traveling clockwise.
Their orbit had the same period as the moon’s orbit around its primary. They were always in a trailing position, shielded from impact with interstellar hydrogen by three thousand miles of rock. At every point of the opposing orbits, the ships were in the lee of the radiation.
He watched the clockwork simplicity of it.
With the moon in six-o’clock position, the rosette of ships was also in six o’clock in its elliptical lunar orbit. It was shielded by both the moon and the bulk of the giant planet itself.
When the moon emerged from that cone of safety, to three-o’clock position, the ships were at the moon’s nine o’clock. But since the moon was by that time tilting its twelve inward toward the giant, the ships were still in a trailing position. With the moon at twelve o’clock, leading the whole procession, the cluster of ships was safely behind it, at the moon’s twelve o’clock. Another quarter turn for both orbiting systems put the moon at nine and the ships at three—still in the moon’s radiation shadow.
The ships’ orbits, he suspected, would have to be adjusted continually to match their period to the moon’s rotation—especially as the mass of the primary shrank. But surely, maneuvering the five ships would require only a fraction of the total energy expenditure eaten up by moving a Jovian or superjovian!
It was beautifully simple and elegant! Jameson watched in admiration for long moments.
Even the deadly probe, with its radiation backlash, was never at the crossroads of the moon’s orbit at the two points where their paths intersected. Everything ticked along beautifully.
“I see,” Jameson said. “Your ships are safe.”
The two Cygnans whistled their approval. Tetrachord wiped the screens and dropped down on four legs. One of his upper limbs twined around Triad in an almost-human gesture of affection.
Jameson blared the sharp fanfare for attention. Startled, the Cygnans jerked their heads in his direction.
“What about Earth? My planet. Will
Consternation. Much twittering back and forth. Jameson had the impression that they had never thought about it, that it hadn’t occurred to them to care.
Finally Tetrachord punched in an inquiry to the ship’s computer, or whatever passed for one aboard the Cygnan vessel. There were flashing images that made no sense to Jameson. They hadn’t bothered to adjust the screen for human vision this time.
Tetrachord twisted around. His eyestalks stretched like taffy in Jameson’s direction.
“Jameson,” the creature said. “We will cross the orbit of your planet when we leave. We will pass close to your sun and swing around it to change direction.”
Jameson got a crawly sensation down his spine. The Cygnan caravan would cross the Earth’s orbit twice.
“Just how close to Earth will you pass?” he asked.
There was no answer for a while. Jameson found he was holding his breath.
The Cygnans wouldn’t have reached anything near light-speed by the time they crossed Earth’s path, of course, so the deadly shower of X-rays that had announced their approach to the solar system would be no danger. But the probe’s deadly drive would be on. That in itself might be enough to sterilize a hemisphere if it got too close and was pointed in the wrong direction. Then, too, there was Jupiter’s own radiation belt, extending millions of miles into space. The Cygnans themselves would be safe from charged particles in the zone swept clean by their moon, but Earth might not be so fortunate.
And there certainly would be tidal effects.
Jameson trembled at the thought of what might happen if a Jupiter-sized mass passed too close to Earth. Earthquakes, floods, perhaps even the breakup of the Earth’s crust.
What if the Earth’s orbit were changed, moved a couple of million miles closer to the sun? Or pulled farther away? Or changed, like Pluto’s, to a more elliptical orbit? Earth’s climate could be permanently altered—an eternal ice age, with much of terrestrial life obliterated, or a water world, steaming under the melted polar caps!
Earth might even be plucked out of orbit to fall into the Sun.
“How close?” he repeated urgently.
“Jameson will be safe,” Triad hummed soothingly. “We will take Jameson with us.”
“Dammit!” he exploded. “That’s not what I asked! What about the
He stopped. He’d unthinkingly used human speech.
They didn’t understand the words, but the violence of his outburst had startled them.
Triad pressed herself against her larger companion. The soft, rat-sized thing plastered to her abdomen reacted to her distress by digging in more firmly with its insectlike legs.
Tetrachord hissed reflexively at Jameson. His upper body stretched to become a foot taller.
Jameson stood facing the alien pair, fists clenched. The kitten had dropped off his lap and scurried away. After a moment, Jameson’s fists fell to his sides. The tension in the bodies of the two Cygnans gradually relaxed.
Jameson stooped over the keyboard of the Moog again and played out his question. “Where will the Earth be
