aster than others. It had
five moons which rotated in the opposite direction from those of any
other satellite system.

It was on the farthest moon, Oberon, a sphere six hundred miles in
diameter, that the Sun-tap station revealed itself. They swung down to
observe it and to place their bomb. Not an H-bomb though--they
recognized that they had erred in thinking they needed such a powerful
explosive.

Oberon was without an atmosphere, a rocky world with streaks of frozen
gases, and here and there the sheen of a lake of ice--ice that would
never melt--that on this world would be a permanent, hard-as-metal
material. There was, nonetheless, something about the surface that
seemed to bother Russ.

"Do you notice what seems to be a sort of shifting movement?" he asked
Burl. Burl looked, and sure enough, he saw that in places there seemed a
flickering of lights.

"Yes," he said, "I see it. What do you suppose it is?"

"I don't know," said Russ, "But I'm going to ask Lockhart to put the
ship down and let me take a look."

Lockhart at first demurred, but finally decided that they could afford
the brief halt. The _Magellan_ approached the surface, safely distant
from the Sun-tap station.

Burl and Russ descended in the two-man rocket plane, while the
teardrop-shaped ship hung half a mile above them. They landed on a
narrow plain, bordered by low ridges of mountains shining with streaks
of frozen hydrogen. A layer of cosmic dust hung over the rocks.

Wearing insulated space suits, they left the rocket plane. It was Burl
who made the first discovery. He pointed dramatically at the ground.
"Look, Russ. This dust is full of streaks and marks. It hasn't been
lying here undisturbed. Something has crossed over it!"

Russ kneeled in order to look more carefully. The layer of dust, the
consequences of an airless world exposed without protection to the
endless fall of cosmic particles, was indeed not the level, undisturbed
surface it should have been. Here and there were light, low depressions,
as if something had moved across it--like a small snake crawling on its
belly. In one place lay a series of depressions, like the footprints of
some light-bodied creature.

"Impossible," muttered Russ. "Life can't exist here."

But they trudged on, across the barren flat to a ridge of rock. Here
they found what they had thought to be impossible. Clustered along the
side of the ridge, in the faint light of the distant and tiny Sun, was