, they had flown planes.

Their vehicles had globe-shaped power plants. Their airplanes had globes
where wings should have been. Their cities and their engines--which
existed now only on wall pictures that were probably once
advertisements--were built along globe-and-rod principles.

"There's no doubt," said Russ, "that the Sun-tapper culture and the
Plutonian culture are the same. It's the descendants of the Plutonians
that we are fighting."

"But how could they have survived?" Burl asked. "This world was never
part of the solar system when it was warm."

"We'll soon know," said Russ. "Tomorrow we're going to see how far we
can get into their polar redoubt. Somehow we've got to blow up that last
station."

"And I think we three are going to do it," said Haines. "The _Magellan_
will never take the place from the sky. We'll have to do it from the
ground."

Now they were reminded of Earth again. For the first time since they had
departed from the United States, night fell. They had not been on any
other planet long enough for such an experience. But the effect here on
Pluto was mild.

Day was like a bright, moonlight night. Night then meant that the dim
Sun had set and, in effect, it merely made the landscape slightly
darker.

They compared notes late into the night in the rocket plane. By dawn,
when again the dim glow shone, they had come to some very definite
conclusions about the planet.

A number of the drawings on the walls seemed to have some religious
significance. They focused on the phases of a moon. There were symbolic
representations of this moon, passing through its phases; presumably
Plutonian religious and social practices were related to it.

"But where is this moon?" Burl had asked.

"I think," Russ answered, "that what some astronomers had suspected
about Pluto was right. It did not originate in the solar system, but was
captured from outer space. Originally it revolved around another sun,
some star which was light-years away. How it tore loose from that star
we'll probably never know--the star might have simply become too dim,
their planet might have been on a shaky orbit, an experiment of theirs
might have jarred it loose, many things could have happened.

"Once beyond the gravitational grip of its parent sun, the planet
wandered through the darkness of interstellar space until it came within
the influence of our own Sun. How long this took would again be a guess.
Possibly not more than