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equatorial zone was one vast, featureless belt of darkish-gray. Its temperate zones were white, with patches of yellow here and there. But its poles were gray again.
"The satellite's like a huge ball of thin mud that's never hardened," said Burl as they studied the strange terrain.
"The equator's the softest it seems to be a river of muddy water, hundreds of miles wide only it can't be water. Probably semisolidified gases holding dust and grains of matter in suspension," said Russ. "The temperate zones are the same stuff, only colder, and therefore more stable. A thin crust of frozen gases over a planet-wide ocean of semiliquid substance."
"The Sun-tap station's on the southern pole," said Burl. "That must be solid."
It was. The poles of Callisto were actually two continent-sized islands of shell. Dry, mudlike stuff, hard as rock, floating en the endless seas of the semiliquid planet.
The station, a ringed setup quite like the one on Earth, stood in the geographic center of the south pole. The Magellan hovered over it while a landing party went down in the four-man rocket plane.
Clyde, Haines and Burl were the landing party. This time, only Burl entered the station after a hole had been blasted in the outer shell. While the redheaded astronomer took samples and made observations, Haines kept watch. Nobody knew what type of defense awaited them here.
Burl found the controls easily enough. He was afraid that he might have lost his physical charge, but it was not so. The controls functioned, the Sun-tap station died. The effect was not very noticeable, for Callisto was already far from the Sun and the thin atmosphere could not diminish the dark sky of outer space. What the great masts caught must have been only the relay from other stations or perhaps the invisible rays of the distant Sun.
Burl saw no reason to linger, and the three of them gathered up their equipment. As they started back toward the rocket plane, they heard an ominous rumble in the ground.