"Do you remember that time," he asked casually. "Twenty-five million years ago, when your ship left Minerva?"

"Twenty-five million years by Earth time," ZORAC pointed out. "It has been less than twenty years by Shapieron time. Yes. I remember all things."

"What kind of world did you leave?"

"I don't fully understand. What kind of kind do you mean?"

"Well, for example, what was the place on Minerva like that you departed from? Was the land flat? Was there water? Were there structures that the Ganymean people had built? Can you describe a picture of it?"

"I can show a picture," ZORAC offered. "Please observe the screen."

Intrigued, Hunt reached out to pick up the wrist unit from where he had placed it on the top of the bedside locker. As he turned it over in his hand the screen came to life with a scene that immediately drew an involuntary whistle of amazement from his lips. He was looking down on the Shapieron , or at least on a vessel that was indistinguishable from it, but this was not the scarred and pitted hulk that he had seen from the bus a few hours before; it was a clean, gleaming, majestic tower of flawless mirror-silver, standing proudly on its tail in a vast open space that was occupied by strange constructions--buildings, cylinders, tubular structures, domes, masts and curves, all interconnected and fused into a single, continuous synthetic landscape. Two other ships were standing there on either side of the first, both just as grand, but somewhat smaller.

The air above the spaceport--for that was what the picture suggested--was alive with all manner of flying vehicles ranging from the very large to the very small, the majority of which moved in well-defined lanes like processions of disciplined skywalking ants.

Behind it all, soaring up for what must have been miles to dominate the skyline, was the city. It was nothing like any city that Hunt had ever seen, but there was nothing else that it could have been. Tier upon tier, level after level, the skyscrapers, terraces, sweeping ramps, and flying bridges clung together in a fantastic composite pattern that seemed to leap into the sky in a series of joyous bounds that defied gravity. The whole construction might have been sculpted by some infinitely skillful cosmic artist from a single monolith of gleaming marble, and yet there were parts of it that seemed to float detached like ivory islands in the sky. Only a knowledge that transcended Man's could have conceived such a feat; it had to be yet another instance of a Ganymean science that remained to be stumbled upon by the scientists of Earth.

"That is the Shapieron as it was before it left Minerva," ZORAC informed him. "The other two ships that traveled with it are there too. The place behind was called Gromos. I don't know what the word is for a place constructed for many Ganymeans to live in."

"A city," Hunt supplied, at the same time feeling an acute inadequacy in the description. "Were the Ganymeans fond of their city?"

"Sorry?"

"Did they like their city? Did they wish very much to be home again?"

"Very much. The Ganymeans were fond of all things on Minerva. They were fond of their home." ZORAC seemed to possess a well-developed ability to sense when further information was needed. "When they left the star, they knew then that their journey home would take a long time. They did not expect all things to be not changed. But they did not expect to find that their home did no longer exist. They are very sad." Hunt had already seen enough to know this. Before he could ask another question, ZORAC spoke up. "Is it okay if I ask questions that are not about English?"

"Yes, all right," Hunt answered. "What do you want to know?"

"The Ganymeans are very unhappy. They believe that the Earthmen destroyed Minerva. Is this true, and if it is, why did they destroy it?"

"No!" Hunt reacted instinctively, with a start. "No. That's not true. Minerva was destroyed fifty thousand years ago. There were no men on Earth then. We came later."

"Did the Lunarians destroy Minerva then?" ZORAC asked. Evidently it had broached this same subject with others on Jupiter Five already.

"Yes. How much do you know about them?"

"Twenty-five million years ago, the Ganymeans took kinds of Earth life from Earth to Minerva. In a short time afterward, the Ganymeans and all kinds of life that were of Minerva and lived on land died. The life kinds from Earth did not die. The Lunarians grew from them and looked like Earthmen now. Other scientific people on Jupiter Five have told me this. This is all I know."

This told Hunt something that he hadn't realized before and hadn't really thought about. Prior to the last few hours, it seemed, ZORAC had been completely ignorant of the Ganymeans having imported large numbers of terrestrial animal species to their own planet. Just to be sure, he had one other question. "The Ganymeans had not brought any Earth life to Minerva before you left to go to the star?"

"I don't know."

"Do you know if they intended to?"

"If they did, I was never told."

"Do you know of any reason why they should wish to?"

"No."

"So whatever the problem was, it must have cropped up later."

"Sorry?"

"The reason must have happened after you left Minerva."

"I think the phrase is'I suppose so.' I can compute no alternative."

Hunt realized with growing excitement that the mystery of what had happened to the Ganymean civilization was one that posed a challenge to both races. Surely, he told himself, their combined knowledge would prove capable of producing the answers. He decided it was time to complete the story of the Lunarians for ZORAC's benefit--the story that had uncovered the most astounding revelations of recent years, even, perhaps, of all time. This story involved a change in our understanding of the structure of the Solar System and required a complete rewriting of the very origins of Mankind.

"Yes, you are right," Hunt said, after a while. "The Lunarians grew--we would say'evolved'--from the forms of Earth life that were left on Minerva after the Ganymeans and other Minervan kinds died out. It took twenty-five million years for them to evolve. By fifty thousand years ago, they had become an advanced race; they built spaceships, machines and cities. Has anybody told you what happened after that?"

"No. But I was intending to ask."

"Is it true that Minerva possessed a moon?"

"A satellite that orbited the planet?"

"Correct."

"Yes."

Hunt nodded to himself in satisfaction. It was as he and the other scientists of Earth had deduced from their investigations of the Lunarian finds.

"And tell me," he asked as a check. "Did Earth possess a moon twenty-five million years ago?"

"No. Earth had no satellite then." Hunt could have been mistaken, but he was sure that ZORAC was learning to convey emotional colorations by the inflection of its voice. He could have sworn that there was surprise in that response.

"Today, Earth has a moon," he said. "It has had a moon for approximately fifty thousand years."

"Since the time when the Lunarians became an advanced race."

"Exactly."

"I see. A connection is clearly implied. Please explain."

"When the Lunarians destroyed Minerva, the planet exploded broke into pieces. The largest piece now orbits the Sun as its most distant planet, Pluto. The other pieces, or most of them, still orbit the Sun between Mars and Jupiter. I assume you know this, since the Ganymeans were surprised when they found that the Solar System had changed."

"Yes, I know about Pluto and the asteroids," ZORAC confirmed. "I knew that the Solar System had changed and that Minerva was not present. But I did not know about the process by which it had changed."