“There are simply too many of them,” Jun Davd said sadly. “A population of half a trillion if we’ve estimated their demographics correctly from that … city.”
Radar imaging had exposed a spongelike warren of habitation that stretched from end to end of the single sprawling continent—an irregular heap of stacked cubes that staggered miles high in places, reaching to where the filthy air thinned to the merely fetid.
The radar imaging had sparked a lot of controversy. There was a strong feeling that the close-up look at Earth should be limited to passive observation—radio eavesdropping, infrared, and the like. But Yggdrasil was a naked-eye object by now, and further caution seemed pointless.
At any rate, the radar didn’t seem to have alerted the inhabitants of the Earth-Moon system. Perhaps their own microwave background was simply too noisy. When there had been no sign that the dragonfly civilization was paying attention to them, the treeload of humans had voted to risk putting Yggdrasil into a remote orbit a hundred thousand miles out, with the fusion engine kept warmed up.
“I thought somehow it would be … lovely,” Mim said, turning a disappointed face to Bram. “Like the Father World seen from space.”
Alis Tonia Atli, now a historian, was among the people who had come crowding into the observatory. “Is it possible that they inherited this? Evolved for it?” the thin woman suggested. “Perhaps it was Original Man who poisoned Terra, millions of years ago. We know he had a population in the billions.”
“No, it wasn’t Original Man that did this,” said a thick-featured man with blue-black ringlets. It was Dal, the dramatist, inspired by the diskworld finds to return to the writing of his verse plays. “Earth didn’t look like this when he was still around. I remember the words of one of the lunar poets of the twenty-eighth century … Taine, I think.”
He struck a professional pose and declaimed:
He was interrupted by Hogard, the librarian. “I don’t think that’s Earth at all. I know it has a large moon, but that one big land mass with its three lobes doesn’t fit any of the maps I’ve seen.”
“Continental drift,” Enry said stolidly. “Seventy-four million years of it. They came together in one supercontinent.”
“The rest of the system doesn’t fit, either,” Hogard said stubbornly. “Where are the gas giants? The solar system was supposed to have four of them, including one with spectacular rings. Instead, those orbits are occupied with a whole collection of terrestroid planets, all of them crawling with dragonflies.”
Jun Davd stepped in. “We know that the moon was terraformed with carbon dioxide from Venus and hydrogen from Jupiter. Carbon dioxide broken down to liberate oxygen, hydrogen reacting with some of the oxygen to make water. We can assume that the process went on. Carbon dioxide and hydrogen are very useful commodities for an industrial society expanding into space. Jupiter and Venus were gradually stripped. Both became habitable. Venus, with the crushing load of its hothouse atmosphere removed and a modest helping of hydrogen brought in to react with liberated oxygen to make oceans—and perhaps even an infusion of cometary ice. And Jupiter—”
“Jupiter stripped down to its rocky core,” Bram said in a flash of insight. “But more important, with that terrible pressure released, the shell of metallic hydrogen surrounding the core could’ve changed state and boiled off. Which would have removed Jupiter’s magnetic field. And with it, the deadly radiation belt that Jovians have.”
Jun Davd nodded approvingly at his former pupil. “Which would have made the moons of Jupiter habitable.”
“Five new worlds,” the stocky playwright, Dal, said. “The four large moons plus Jupiter itself. All the real estate Original Man could have used. Seven, counting Mars and Venus. That bears me out. Original Man was not responsible for that stinking stew down there!”
He gestured vehemently at the observation window, where the blotched brown world floated against the cleanliness of space.
“No, they have abused their legacy most grieviously,” murmured Jun Davd. “Original Man once had a ring city and linked synchronous satellites draped around the waist of his lovely world, did you know that?”
There were oohs and ahs from the visitors. While Jun Davd explained, Bram turned his attention to the most interesting of the holographic displays that had been set up around the observatory—the one produced by gravitational imaging. It showed a tangled belt of overgrown wreckage around the equator of the slowly revolving planet, The buried debris must have been millions of years old. It made ridges in the sea floor, a single straight line of low hills across the land. The devastation when it crashed must have been inconceivable. Perhaps it had been the planetary disaster that had cleared an evolutionary path for the ascent of the rat-people.
Hogard was still insistent. “Okay, there are five rocky worlds doing a complicated dance around one another where Jupiter ought to be. But what about the other three gas giants this system is supposed to have? Did Original Man strip them, too?”
“No!” Mim cried with sudden heat. “I’ve seen the pictures of Saturn’s rings! Human beings never would have done that to her!”
Bram followed her gaze to the long gallery wall of planetary images that Jun Davd had put on display. It was a selection made from the hundreds that had been taken while Yggdrasil plunged through the Sol system. The one that upset Mim showed a grim, yellow-stained ball of rock where a scummy ocean lapped at a tarnished shore. Yggdrasil had passed within a million miles of it. Even at that distance one could distinguish the scab of habitation that covered much of the land surface.
“I agree, Mim,” Jun Davd said. “Perhaps the rat-people did that. Saturn was the next world out. They may not have had our sense of aesthetics.”
“Atmospheric mining is simple in principle,” Bram said. “A satellite in low orbit with a couple of hundred miles of siphon suspended beneath it. The vacuum of space operates the siphon. The orbit has to be readjusted every once in a while to compensate for atmospheric drag on the hose, but there’s plenty of reaction mass available to do it with. The rat-people could have mined their hydrogen that way and had another planet available after Saturn was sucked dry.”
“Eight planets,” Jun Davd said. “Of Saturn’s satellites, seven are more than three hundred miles in diameter—including one moon as big as Mercury—and the dragonflies are using them all.”
“That wasn’t enough for them,” Bram said grimly. “We’ve detected dragonfly broadcasts from the leftover cores of what must have been Uranus and Neptune—and all of their moons that we were able to get any separation on.”
“They’re breeders!” Dal blazed. “Any piece of rock big enough for them to light on!”
“Yes, indeed,” Jun Davd agreed. “Our resident sociobiologist, Heln Dunl-mak, tells me that she estimates the total dragonfly population of Sol system to be more than ten trillion.”
The figure was mind-boggling—too big to grasp. Bram heard the gasps around him.
“And they’re pushing outward,” Jun Davd went on. “If the diskworld system of Delta Pavonis represents their present limit of expansion, then they now occupy a volume of space forty light-years in diameter.”
He was about to go on, when an alarm went off. He picked up an interphone and listened briefly. He reached out and switched on a display. “Yes, yes, I see them now,” he said.