The dome had become very quiet. Grim faces looked out over the scene, each one an impenetrable mask preserving the privacy of thoughts that were not for sharing. No video record would ever recapture the feelings of this moment, whatever it might show, however many times it might be seen.

After a while, a sergeant who was standing next to Hunt turned his head a fraction. "Man, I don't know," he muttered quietly. "What a hell of a way to come home."

"What a hell of a home to come home to," Hunt replied.

The accommodations available at Main were not sufficient to hold all the Ganymeans, who numbered more than four hundred, so the majority were obliged to remain in the Shapieron. Nevertheless, just being on a firm surface again, even if it was only the frozen ball of rubble called Ganymede, and among other beings, seemed to provide the aliens with a badly needed psychological tonic. Earthmen showed them the facilities and amenities that were available in their new quarters, pointed out the stocks of supplies and food-stuffs provided for experimentation, and the various other items which, it was hoped, would help to make life reasonably comfortable. Meanwhile other UNSA crews delivered similar loads, hurriedly ferried from one of the orbiting freighters, to the Ganymeans still inside their ship. Then the new arrivals were left in peace and to their own devices.

After a much-needed rest, they announced that they were ready to resume their dialogue with their hosts. Accordingly, an evening conference was arranged between the leaders and certain other individuals of the two races, to be held in the officers' mess and to be followed by a formal welcoming dinner. Hunt was among those invited to attend; so was Danchekker.

The temperature had originally been lowered to make the Ganymeans feel more at home, but by the time everybody had been crammed into the officers' mess for an hour or more and palls of tobacco smoke were hanging sullenly beneath the lights, it turned out to be just as well for all. Danchekker finished what he had been saying into the microphone of the headset that he was wearing over his sweater, then resumed his seat. Garuth replied from the far end of the room, where the Ganymean contingent was concentrated.

"I think I'd better let a scientist answer a scientist on that one, Professor." He looked down and behind him at one of the other Ganymeans. "Shilohin, will you respond?" All the Earthmen present who did not possess Ganymean kits had been equipped with headsets similar to Danchekker's and could thus follow ZORAC's translation of the proceedings. The machine's ability in this respect was now quite passable although, mainly as a result of having conversed with many and varied individuals, it had not yet fully established a way to disentangle formal English constructions from American colloquialisms, a defect that sometimes yielded hilarious results.

Shilohin, the chief scientist of the Ganymean expedition, had already been introduced to the company. As Garuth sat down to make room, she rose to her feet and spoke. "First, I must congratulate the scientists of Earth for their superb piece of figuring out. Yes, as Professor Danchekker has just suggested, we Ganymeans do not enjoy a high tolerance to carbon dioxide. He and his colleagues were also absolutely correct in the picture that they had deduced of conditions on Minerva at the time of our departure--a planet that they had not even seen."

Shilohin paused a moment, waiting for that much to sink in. Then she continued. "The average concentration of radioactive, heat-producing substances in Minervan rocks was somewhat higher than is found on Earth. The interior of Minerva was thus hotter and molten to a greater degree, and the crust was thinner. The planet was therefore more active volcanically than Earth, a tendency that was further complicated by the strong tidal forces induced in the crust by Luna, which orbited closer to Minerva than it does to Earth today. This high level of volcanic activity released large quantities of carbon dioxide and water vapor into the atmosphere, resulting in a greenhouse effect that sustained a high enough surface temperature for the oceans to remain liquid and life to emerge. By terrestrial standards it was still sure-as-hell cold, but not nearly as cold as it would have been otherwise.

"This situation had always existed throughout the history of Minerva. By the time that our civilization was at its peak, however, a new epoch of tectonic activity was just beginning. The level of carbon dioxide in the atmosphere began showing a measurable increase. It soon became clear that it would only be a matter of time before the level grew beyond the point we could tolerate. After that our world would become, for us, uninhabitable. What could we do?" Shilohin let the question hang and cast her eyes around the room, apparently inviting the Earthmen to start a discussion.

After a few seconds a UNSA engineer at the back responded. "Well, we've seen some pretty remarkable examples of the kind of technology that you people had. I wouldn't have thought you'd have found it much of a problem to figure out some way of simply winding the level back down again . . . some kinda planetwide climatic control, I guess. . . sump'n like that."

"Commendably on the ball," she said, with something that they took to be the equivalent of an approving nod. "We did in fact employ planetary climatic control to some degree, primarily to limit the extent of the Minervan ice caps. But when it came to tinkering with the chemical composition of the atmosphere, we were less certain of our ability to keep everything sufficiently under control; the balance was very delicate." She looked directly at the questioner. "A scheme along the lines you suggest was in fact proposed, but mathematical models indicated that there was too high a risk of destroying the greenhouse effect completely, and so of guaranteeing the end of life on Minerva even more quickly. We are a cautious people and do not take risks readily. Our government threw the idea out."

She remained silent and allowed them time to think of other possibilities. Danchekker didn't bother to raise the notion that they might have tried importing terrestrial plant life as an attempt at introducing a compensatory mechanism. He already knew full well that the Ganymeans knew nothing of such a venture. Presumably that solution had been tried after Garuth's expedition had departed. Further analyses by his scientists and discussions with ZORAC had indicated if that had been the objective of the exercise, it would not have succeeded anyway--a point that would surely not have escaped the Ganymean scientists at the time. For the moment this event was still as much a mystery as ever.

Eventually Shilohin spread her arm wide as if appealing to a class of children who were being a little slow that day. "Logically it's very simple," she said. "If we left the carbon-dioxide level to rise, we would die. Therefore we could not allow it to rise. If we prevented the rise, as we could have done, there would have been too much of a risk of freezing the whole planet solid because the carbon dioxide kept Minerva warm through the greenhouse effect. We needed the results of the greenhouse effect to keep us warm because we were a long way from the Sun. Hence, we wouldn't need it at all if we were nearer the Sun, or if the Sun were warmer."

Some of the faces in front of her remained blank; some suddenly looked incredulous. "It's easy then," a voice called from near Hunt. "All you had to do was move Minerva in a bit or heat up the Sun." He meant that as a joke but the Ganymean began nodding her head in imitation of the human mannerism.

"Exactly," she said. "And those were the two conclusions we arrived at, too." A few gasps of amazement came from various parts of the room. "Both possibilities were studied extensively. Eventually a team of astrophysicists convinced the government that warming up the Sun was the more practicable. Nobody could find a flaw in the calculations, but, as always, our government was cautious and elected not to blow a wad on fooling around with the Sun. They wanted to see some proof first that the plan would work. . . Yes, Dr. Hunt?" She had noticed his hand hail raised to attract attention.