"What is it, Rog?" Garuth's face turned away to look at another screen.
"We still have a fault on the primary retardation system for the main-drive toroids. If we start up those drives, the only way they'll ever slow down again is at their own natural rate. The whole braking system's been stripped down. We could never put it together again in under twenty hours, let alone trace the fault and fix it."
Garuth thought for a moment. "But we can start them up okay?"
"We can," Jassilane confirmed. "But once those black holes start whirling round inside the toroids, the angular momentum they'll build up will be phenomenal. Without the retardation system to slow them down, they'll take years to coast down to a speed at which the drives can be deactivated. We'd be under main drive all the time, with no way of shutting down." He made a helpless gesture. "We could end up anywhere."
"But we've no choice," Garuth pointed out. "It's fly or fry. We'll have to set course for home and orbit the Solar System under drive until we've dropped to a low enough return velocity. What other way is there?"
"I can see what Rog's getting at," the chief scientist interjected. "It's not quite as simple as that. You see, at the velocities that we would acquire under years of sustained main drive, we'd experience an enormous relativistic time-dilation compared to reference frames moving with the speed of Iscaris or Sol. Since the Shapieron would be an accelerated system, much more time would pass back home than would pass on board the ship; we know where we'd end up all right . . . but we won't be too sure of when. "
"And, in fact, it would be worse than just that," Jassilane added. "The main drives work by generating a localized space-time distortion that the ship continuously'falls' into. This also produces its own time-dilation effect. Hence you'd have the compound effect of both dilations added together. What that would mean with an unretarded main drive running for years, I couldn't tell you--I don't think anything like it has ever happened."
"I haven't done any precise calculations yet, naturally," the chief scientist said. "But if my mental estimates are anything to go by, we could be talking about a compound dilation of the order of millions."
"Millions?" Garuth looked stunned.
"Yes." The chief scientist looked out at them soberly. "For every year that we spend slowing down from the velocity that we'll need to escape the nova, we could find that a million years have passed by the time we get home."
Silence persisted for a long time. At last Garuth spoke in a voice that was heavy and solemn. "Be that as it may, to survive we have no choice. My orders stand. Chief Engineer Jassilane, prepare for deep-space and bring the main drives up to standby readiness."
Twenty hours later the Shapieron was under full power and hurtling toward interstellar space as the first outrushing front of the nova seared its hull and vaporized behind it the cinder that had once been Iscaris III.
Chapter One
In a space of time less than a single heartbeat in the life of the universe, the incredible animal called Man had fallen from the trees, discovered fire, invented the wheel, learned to fly and gone out to explore the planets.
The history that followed Man's emergence was a turmoil of activity, adventure and ceaseless discovery. Nothing like it had been seen through eons of sedate evolution and slowly unfolding events that had gone before.
Or so, for a long time, it had been thought.
But when at last Man came to Ganymede, largest of the moons of Jupiter, he stumbled upon a discovery that totally demolished one of the few beliefs that had survived centuries of his insatiable inquisitiveness: He was not, after all, unique. Twenty-five million years before him, another race had surpassed all that he had thus far achieved.
The fourth manned mission to Jupiter, early in the third decade of the twenty-first century, marked the beginning of intensive exploration of the outer planets and the establishment of the first permanent bases on the Jovian satellites. Instruments in orbit above Ganymede had detected a large concentration of metal some distance below the surface of the moon's ice crust. From a base specially sited for the purpose, shafts were sunk to investigate this anomaly.
The spacecraft that they found there, frozen in its changeless tomb of ice, was huge. From skeletal remains found inside the ship, the scientists of Earth reconstructed a picture of the race of eight-foot-tall giants that had built it and whose level of technology was estimated as having been a century or more ahead of Earth's. They christened the giants the "Ganymeans," to commemorate the place of the discovery.
The Ganymeans had originated on Minerva, a planet that once occupied the position between Mars and Jupiter but which had since been destroyed. The bulk of Minerva's mass had gone into a violently eccentric orbit at the edge of the Solar System to become Pluto, while the remainder of the debris was dispersed by Jupiter's tidal effects and formed the Asteroid Belt. Various scientific investigations, including cosmic-ray exposure-tests on material samples recovered from the Asteroid Belt, pinpointed the breakup of Minerva as having occurred some fifty thousand years in the past--long, long after the Ganymeans were known to have roamed the Solar System.
The discovery of a race of technically advanced beings from twenty-five million years back was exciting enough. Even more exciting, but not really surprising, was the revelation that the Ganymeans had visited Earth. The cargo of the spacecraft found on Ganymede included a collection of plant and animal specimens the likes of which no human eye had ever beheld--a representative cross section of terrestrial life during the late Oligocene and early Miocene periods. Some of the samples were well preserved in canisters while others had evidently been alive in pens and cages at the time of the ship's mishap.
The seven ships that were to make up the Jupiter Five Mission were being constructed in Lunar orbit at the time these discoveries were made. When the mission departed, a team of scientists traveled with it, eager to delve more deeply into the irresistibly challenging story of the Ganymeans.
A data manipulation program running in the computer complex of the mile-and-a-quarter-long Jupiter Five Mission command ship, orbiting two thousand miles above Ganymede, routed its results to the message-scheduling processor. The information was beamed down by laser to a transceiver on the surface at Ganymede Main Base, and relayed northward via a chain of repeater stations. A few millionths of a second and seven hundred miles later, the computers at Pithead Base decoded the message destination and routed the signal to a display screen on the wall of a small conference room in the Biological Laboratories section. An elaborate pattern of the symbols used by geneticists to denote the internal structures of chromosomes appeared on the screen. The five people seated around the table in the narrow confines of the room studied the display intently.
"There. If you want to go right down to it in detail, that's what it looks like." The speaker was a tall, lean, balding man clad in a white lab coat and wearing a pair of anachronistic gold-rimmed spectacles. He was standing in front and to one side of the screen, pointing toward it with one hand and clasping his lapel lightly with the other. Professor Christian Danchekker of the Westwood Biological Institute in Houston, part of the UN Space Arm's Life Sciences Division, headed the team of biologists who had come to Ganymede aboard Jupiter Five to study the early terrestrial aninials discovered in the Ganymean spacecraft. The scientists sitting before him contemplated the image on the screen. After a while Danchekker summarized once more the problem they had been debating for the past hour.
"I hope it is obvious to most of you that the expression we are looking at represents a molecular arrangement characteristic of the structure of an enzyme. This same strain of enzyme has been identified in tissue samples taken from many of the species so far examined in the labs up in J4. I repeat--many of the species . . . many different species . . ." Danchekker clasped both hands to his lapels and gazed at his miniaudience expectantly. His voice fell almost to a whisper. "And yet nothing resembling it or suggestive of being in any way related to it has ever been identified in any of today's terrestrial animal species. The problem we are faced with, gentlemen, is simply to explain these curious facts."