s 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.

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