d after the lord of the underworld,
Pluto.

The _Magellan_ plunged on, in constant acceleration, moving outward to
the farthest limit of the solar system. They had traveled almost one
billion, eight hundred million miles from the Sun--and yet they still
had two billion miles more to go. This was the longest stretch--and
during it, they would reach speeds greater than any they had touched
before. They shot outward, faster and faster, eating up the infinite
emptiness of space, driving the vast stretch that divided Pluto from its
neighbors.

The Sun, already small, dwindled steadily. It was still the brightest
star in their sky--of all the stars, it alone retained a disclike shape,
and the faint flicker of its coronal flames could occasionally be made
out--but it no longer dominated the heavens. To find the Sun, they now
had to look for it as they would for any other star.

As for Earth, it could not be seen. So close to the tiny Sun it lay that
only their sharpest telescopes could bring it out. Even Jupiter showed
up only as a thin, tiny crescent near the solar point of light.

"Pluto's a mysterious world," said Burl as he and Russ scanned the
heavens for a first glimpse of it. "The accounts in your astronomy books
give very little real information on it--but what they give is strange.
They say it's the only planet beyond Mars that is a small solid world
like the inner ones. It seems to be the same size as Earth--not at all
like the big outer worlds. And they say it seems to be the same mass as
Earth--a solid world whose surface gravity would be the same as our own
planet's."

Russ nodded. "It's an odd one, all right. There's now even some belief
that it's not a true planet, but one that was once a satellite of
Neptune. Its orbit is peculiar; it apparently may cut into that of
Neptune. In fact, everything hints at Pluto not being a true child of
our Sun. It may be a world captured from afar--a lonely wanderer cast
off from some other star, captured by the Sun after millions of years of
drifting lightless through space."

Beyond them, in their vision, lay only the stars of outer space, the
void that did not belong to our system. And then, finally, they found
Pluto--a tiny point of light shining among the blazing stars. They saw
the disc, dimly reflected in the light of the far-away Sun.

Even as they were taking their first long look at the dark planet, the
general alarm rang. They had caught up with the fleeing wr