As the radius of Phobos's circle was far shorter than that of the
parabolic curve they were making, it began to draw away, and was
rapidly left behind. Applying the full apergetic force to Mars
and the larger moon, they shot away like an arrow, having had
their speed increased by the planet's attraction while
approaching it, and subsequently by repulsion.

"Either of those," said Bearwarden, looking back at the little
satellites, "would be a nice yacht for a man to explore space on.
He would also, of course, need a sun to warm him, if he wished to
go beyond this system, but that would not have to be a large
affair--in fact, it might be smaller than the planet, and could
revolve about it like a moon."

"Though a sun of that size," replied Cortlandt, "might retain its
heat for the time you wished to use it, the planet part would be
nothing like as comfortable as what we have here, for it would be
very difficult to get enough air-pressure to breathe on so small
a body, since, with its slight gravitation-pull, to secure
fifteen pounds to the square inch, or anything like it, the
atmosphere would have to extend thousands of miles into space, so
that on a cloudy day you would be in darkness. It would be
better, therefore, to have such a sun as you describe and
accompany it in a yacht or private car like this, well stocked
with oxygen and provisions. When passing through meteoric swarms
or masses of solid matter, collision with which is the most
serious risk we run, the car could follow behind its sun instead
of revolving around it, and be kept from falling into it by
partially reversing the attraction. As the gravitation of so
small a sun would be slight, counteracting it for even a