The professor's arm had suddenly become paralyzed and was holding a fork in midair with half a roast potato impaled on the end. "You mean that all the native Minervan land life disappeared—just like that?"

"Well, during a fairly short time, anyway. We've been asking for a long time what happened to the Ganymeans. Now it looks more as if the question should be phrased in even broader terms: What happened to the Ganymeans and all their land-dwelling relatives?"

Chapter Twenty-One

For weeks the two scientists debated the mystery of the abrupt disappearance of the native Minervan land dwellers. They ruled out physical catastrophe on the assumption that anything of that kind would have destroyed the terrestoid types as well. The same conclusion applied to climatic cataclysm.

For a while they considered the possibility of an epidemic caused by microorganisms imported with the immigrant animals, one against which the native species enjoyed no inherited, in-built immunity. In the end they dismissed this idea as unlikely on two counts: first, an epidemic sufficiently virulent in its effects to wipe out each and every species of what must have numbered millions, was hard to imagine; second, all information received so far from Ganymede suggested that the Ganymeans had been considerably farther ahead in technical knowledge than either the Lunarians or mankind—surely they could never have made such a blunder.

A variation on this theme supposed that germ warfare had broken out, escalated, and got out of control. Both the previous objections carried less weight when viewed in this context; in the end, this explanation was accepted as possible. That left only one other possibility: some kind of chemical change in the Minervan atmosphere to which the native species hadn't been capable of adapting but the terrestoids had. But what?

While the pros and cons of these alternatives were still being evaluated on Jupiter Five, the laser link to Earth brought details of a new row that had broken out in Navcomms. A faction of Pure Earthists had produced calculations showing that the Lunarians could never have survived on Minerva at all, let alone flourished there; at that distance from the Sun it would simply have been too cold. They also insisted that water could never have existed on the surface in a liquid state and held this fact as proof that wherever the world shown on Charlie's maps had been, it couldn't have been anywhere near the Asteroids.