Seen through a telescope, Jupiter shows the loveliest variety of
colors, with the reddish ones always most conspicuous. The slightly
pink-tinted steady light that we get from the planet with the naked eye
in no way suggests the turbulent, flame-like aspect that a telescopic
view opens to us. The telescope also reveals very clearly that
flattening at the poles which has already been spoken of.
With so dense an atmosphere as Jupiter most likely has, it is sometimes
doubtful whether his surface can be seen by us at all. But it is
certain that we see something apparently much more dense and stable
than an atmosphere is supposed to be; and hence it is thought that, in
spite of its thickness, the atmosphere may be only partially opaque,
and that it may be in some places even more or less transparent.
It does not seem probable that the markings on Jupiter are wholly
atmospheric. Some of them indicate that the substance we see has
considerably more consistency than a mere gas. The whole surface of
the planet is covered with belts and spots of various colors and
varying shapes. The belted appearance is particularly marked. It has
been noticed for more than two hundred years, and can be seen with a
comparatively small telescope. Sometimes as many as twenty or thirty
belts have been seen at one time. All of them are parallel with the
equator.
Two broad red belts on each side of the equator, called the tropical
belts, are very distinct, and sometimes retain the same shape and
color for months at a time, though sometimes they change rapidly in
both color and outline. Between them is the equatorial belt, which
is also a semi-permanent feature, remaining often for a considerable
period unchanged. These belts, and the spots that sometimes appear on
and near them, have been closely watched, because about the equator,
and especially just south of it, is the region of greatest activity on
Jupiter’s surface.
One feature that more nearly suggests solidity and permanency than
anything else on Jupiter is the famous great red spot which lies in the
southern hemisphere just below the southern tropical belt. It appeared
about thirty-five years ago, in July, 1878, as a pale pink spot, grew
brighter for two or three years, and then faded, until, at the end of
two or three more years, it was almost invisible. In another year it
came again, and increased in brightness for five or six years. Then it
grew a little fainter, and has since remained a rather faint red spot,
but plainly visible.
In shape the great red spot is an immense oval as much as thirty
thousand miles from east to west and seven thousand miles from north
to south, which gives it a surface four or five times as large as the
land area on the entire earth, and larger even than the whole surface
of the earth including the oceans. Although retaining its own shape,
it seems to drift about among its surroundings, showing that it is not
attached to any solid surface; and yet it has a suggestion of solidity
in itself, which was shown when it and another smaller spot were seen
to be drifting toward each other, and then finally to meet. Instead of
colliding or going over or under, they calmly drifted to one side and
went around each other.
Appearances such as this have suggested the idea that the great spot
might be a continent in process of formation. Such an idea is at best a
speculation; but it would be interesting if it should prove that we are
witnessing on Jupiter the process through which our own earth must at
one time have passed when its crust began to solidify in patches, as
one of the steps in the long period of evolution which has prepared it
for our uses. It is not at all certain that Jupiter will ever be just
like the earth. The differences between its atmosphere and ours may
have some influence in its development that we have little knowledge
of at present, and there are some other fundamental differences
between the two planets which may in some way effect a difference in
development. But in a general way we know that the planet will in time
become more condensed than it now is and will finally solidify. Whether
the processes will be carried on in just the same way in which they
have been here on the earth is not so certain.