"That's it," said Kim. "That's the sun Alis. There should be four planets, but we're looking for Number One. It goes out beyond Two at aphelion, so we have to check the orbit--if we can find it--before we can be sure. No--we should be able to tell by the rotation. Very slow." "And what are you going to do with it?" demanded Dona. There were bright spots in emptiness which the electron telescope instantly declared to be planets. Kim set up cameras for pictures. "Alis One is the only really uninhabitable planet in the Galaxy that's inhabited," he observed painstakingly. "It belongs to Pharos Three. I understand it's the personal property of the king. It has no atmosphere in spite of an extremely high specific gravity and a reasonable mass. But the plutonium mines have been worked for five thousand years." "Plutonium mines with that half-life?" Dona said skeptically. "You must be joking!" "No," said Kim. "It's a very heavy planet, loaded with uranium and stuff from bismuth on out. It has an extremely eccentric orbit. As I told you, at aphelion it's beyond the orbit of Pharos Two. At perihelion, when it's nearest to its sun, it just barely misses Roche's Limit--the limit of nearness a satellite can come to its primary without being torn apart by tidal strains. And at its nearest to its sun, it's bombarded with everything a sun can fling out into space from its millions of tons of disintegrating atoms. Alpha rays, beta rays, gamma particles, neutrons, and everything else pour onto its surface as if it were being bombarded by a cyclotron with a beam the size of a planet's surface. You see what happens?" Dona looked startled. "But, Kim, every particle of the whole surface would become terrifically radioactive. It would kill a man to land on it!" "According to my merchant-prince friend on Spicus Five, it did kill the first men to set foot on it. But the point is that its heavy elements have been bombarded, and most of its uranium has gone on over to plutonium and americium and curium. In ancient days, when it went out on the long sweep away from its sun, it cooled off enough for men to land on it at its farthest-out point. With shielded space-suits they were able to mine its substance for four to five months before heat and rising induced radio-activity drove them off again. Then they'd wait for it to cool off once more on its next trip around. "They went to it with space-ships, and the last space-line in the First Galaxy ran plutonium and americium and the other radio-actives to a matter-transmitter from which they could be distributed all over the Galaxy. But it wasn't very efficient. They could only mine for four or five months every four years. All their equipment was melted and ruined when they were able to land again. A few hundred years ago, however, they solved the problem." Dona stared out the vision-ports. There were two planets which might be the one in question. But there were only three in sight.