ore minds that work at a problem, the sooner it will be solved. The
discovery of a means of negating, reversing or otherwise utilizing the
immense force of gravitation for space flight purposes is now thought to
be within the bounds of probability. It should occur some time within
the next hundred years, possibly in even the short period I assume here.

Once solved, the severe handicaps imposed on space exploration by the
weight and chemical limitations of rockets would no longer apply. The
whole timetable of our conquest of the planets in our solar system would
be tremendously speeded up, from hot Mercury all the way out to frigid
Pluto.

In describing the visits of the spaceship _Magellan_ to the planets, I
have endeavored to adhere to known facts and the more reasonable
assumptions about each of these worlds. The planet Pluto, however,
deserves further comment, occupying as it does both an important role in
this adventure and a unique one in actual astronomical lore.

Back at the dawn of this century, many astronomers, and notably Dr.
Percival Lowell, studied certain irregularities in the orbit and motion
of Neptune, at that time believed to be the outermost planet. They
decided that these eccentricities (or perturbations, as they are called)
could only be caused by the presence of another, yet undiscovered planet
beyond Neptune.

Following this line of research, a young astronomer, Dr. Clyde Tombaugh,
working at Lowell's own observatory, was able to announce on March 13,
1930, that he had finally found this ninth world, which he named Pluto.

In the years that have followed, Pluto has proven to be a truly puzzling
planet. Unlike its neighbors from Jupiter outward, it is not a giant
world, light and gaseous in nature. Instead, it belongs physically to
the small, dense inner planets of which Earth is one.

The latest viewpoint on this planet, whose size and weight seem quite
like those of Earth, is that it may not be a true child of the Sun, but
an outsider captured as it roamed the trackless realms of galactic
space. Its orbit is highly eccentric and rather lopsided, taking it as
far away from the Sun as four and a half billion miles and as close to
the Sun as two and three-quarter billion miles, thereby cutting inside
the orbit of Neptune itself. In fact, during the period from 1969 to
2009 (covering most of the lifetimes of the younger readers of this
book) Pluto will not be the ninth planet, but the eighth, f