A sudden spurt of blazing gas shot up from the center of the station. "Duck!" yelled Haines, and they fell flat on the ground. Burl held his hands protectively over his head, as an explosion shook the building. There was no rain of rocks. Whatever the blast, Callisto's gravity was too weak to attract the debris that flew high above the station. "It was an atomic explosion!" Haines shouted into his helmet mike. "They mined the station. Run for it!" They raced for the rocket plane. As they ran, Burl felt the ground quiver beneath him, and huge cracks began to spread, rippling through the hard ground. They reached the plane and piled in. Russ took off just as the surface cracked open in a thousand places like an ice sheet breaking in an Arctic thaw. As they rocketed back to the _Magellan_, the whole polar cap, an area hundreds of miles around the Sun-tap station, split apart. Great spurts of liquid magma, the liquid gas-dust from the heart of the planet, shot up like fountains. Parts of the shell-like polar continent were disappearing beneath this new ocean. "Their little atomic bomb shattered the thin crust. The whole polar island will probably sink," said Russ. "It was a clever trap. They knew what would happen." "Saturn next," said Burl. "What'll they have set up there?" They reached the _Magellan_, loaded the rocket plane aboard, and pulled out, setting their course for the ringed planet. But even as they did so, something was coming from Saturn to meet them. Chapter 14. _Rockets Away!_ The next lap of their journey was uneventful. Saturn, the next outward planet from the Sun, and the second largest, would present the same problem as Jupiter. This world, famous for its mysterious rings, was about 71,000 miles in diameter and had a large family of satellites--nine in all. The Sun-tap station would be on one of these, Burl thought. Saturn was also almost as far out from Jupiter as Jupiter itself had been from the Sun. This meant that the trip would be as long for the _Magellan_ as the distance they had already traveled to get to Jupiter. Fortunately the A-G drive was a remarkable thing--it was possible to accelerate to fantastic speeds--in theory, probably right up to the speed of light. And so, where great distances were concerned, the ship simply rushed its fall through on Saturn's line of gravitation. Boulton had fully recovered and showed no lingering signs of the strange electronic charge. Because of the limited size of the crew, Lockhart put the Marine captain back on full duty--he would participate in future landings as if nothing had ever happened. At the same time, Lockhart cautioned Haines, Burl and Ferrati to keep their eyes on him. It was always possible that the foe's weapon had made some more lasting mark.