Other Worlds | Page 6

respect, just as they are all alike in receiving light and
heat from the sun.
This preliminary judgment, arising from the evident unity of the

planetary system, can only be varied by an examination of its members
in detail.
One striking fact that commands our attention as soon as we have
entered the narrow precincts of the solar system is the isolation of the
sun and its attendants in space. The solar system occupies a
disk-shaped, or flat circular, expanse, about 5,580,000,000 miles across
and relatively very thin, the sun being in the center. From the sun to the
nearest star, or other sun, the distance is approximately five thousand
times the entire diameter of the solar system. But the vast majority of
the stars are probably a hundred times yet more remote. In other words,
if the Solar system be represented by a circular flower-bed ten feet
across, the nearest star must be placed at a distance of nine and a half
miles, and the great multitude of the stars at a distance of nine hundred
miles!
Or, to put it in another way, let us suppose the sun and his planets to be
represented by a fleet of ships at sea, all included within a space about
half a mile across; then, in order that there might be no shore relatively
nearer than the nearest fixed star is to the sun, we should have to place
our fleet in the middle of the Pacific Ocean, while the distance of the
main shore of the starry universe would be so immense that the whole
surface of the earth would be far too small to hold the expanse of ocean
needed to represent it!
From these general considerations we next proceed to recall some of
the details of the system of worlds amid which we dwell. Besides the
earth, the sun has seven other principal planets in attendance. These
eight planets fall into two classes--the terrestrial planets and the major,
or jovian, planets. The former class comprises Mercury, Venus, the
earth, and Mars, and the latter Jupiter, Saturn, Uranus, and Neptune. I
have named them all in the order of their distance from the sun,
beginning with the nearest.
The terrestrial planets, taking their class name from terra, the earth, are
relatively close to the sun and comparatively small. The major
planets--or the jovian planets, if we give them a common title based
upon the name of their chief, Jupiter or Jove--are relatively distant from

the sun and are characterized both by great comparative size and slight
mean density. The terrestrial planets are all included within a circle,
having the sun for a center, about 140,000,000 miles in radius. The
space, or gap, between the outermost of them, Mars, and the innermost
of the jovian planets, Jupiter, is nearly two and a half times as broad as
the entire radius of the circle within which they are included. And not
only is the jovian group of planets widely separated from the terrestrial
group, but the distances between the orbits of its four members are
likewise very great and progressively increasing. Between Jupiter and
Saturn is a gap 400,000,000 miles across, and this becomes
900,000,000 miles between Saturn and Uranus, and more than
1,000,000,000 miles between Uranus and Neptune. All of these
distances are given in round numbers.
Finally, we come to some very extraordinary worlds--if we can call
them worlds at all--the asteroids. They form a third group,
characterized by the extreme smallness of its individual members, their
astonishing number, and the unusual eccentricities and inclinations of
their orbits. They are situated in the gap between the terrestrial and the
jovian planets, and about 500 of them have been discovered, while
there is reason to think that their real number may be many thousands.
The largest of them is less than 500 miles in diameter, and many of
those recently discovered may be not more than ten or twenty miles in
diameter. What marvelous places of abode such little planets would be
if it were possible to believe them inhabited, we shall see more clearly
when we come to consider them in their turn. But without regard to the
question of habitability, the asteroids will be found extremely
interesting.
In the next chapter we proceed to take up the planets for study as
individuals, beginning with Mercury, the one nearest the sun.
CHAPTER II
MERCURY, A WORLD OF TWO FACES AND MANY
CONTRASTS

Mercury, the first of the other worlds that we are going to consider,
fascinates by its grotesqueness, like a piece of Chinese ivory carving,
so small is it for its kind and so finished in its eccentric details. In a
little while we shall see how singular Mercury is in many of the
particulars of planetary existence, but first of