Page:Popular Science Monthly Volume 89.djvu/692

 Is Jupiter Launching a Moon?

The mysterious Great Red Spot on the biggest of planets and what it means to astronomers

��IF JUPITER were cut up into one thousand three hundred pieces, each would be larger than the Earth. All the planets together do not weigh half as much as Jupiter. Only the Sun surpasses Jupiter in size.

A year on the planet Jupiter is equal to twelve of our years. Jupiter rotates on his axis in less than half the time of the Earth. But because of the planet's enormous size, the rotation speed is much higher. While the Earth travels 17 miles a minute, Jupiter travels 466 miles a minute. If Jupiter turned on its axis a little faster, it would burst as some flywheels do, when they exceed a safe speed.

Jupiter may be regarded either as a decaying sun or a developing earth. He has not yet had time to cool. He is a great globe of gaseous and molten • matter — the most extraordinary planet in the entire solar system.

Because Jupiter is a semi-sun, there is some reason to believe that he possesses inherent light of his own. But astrono- mers are by no means in accord on this point. Perhaps the clouds, that certainly exist on Jupiter, owe their origin to some other heat than that of the Sun. In other words, Jupiter possesses stores of heat within liimselt.

Look at Jupiter through a fairK' pow- erful telescope and you will see two broad belts with two or three narrower ones on either side. They lie practically jiarallel to the planet's equator. Some- times they are narrow, and when they are very narrow, there is an increase in their number.

Since Jui)iter is in a more or less fluid condition, he is surrounded by a dense, cloudy envelojie. In all likelihood, the belts are simply rifts in this envelope, exposing the more solid portion of the planet beneath. Not mtich is known about the bi-lts. While they remain unchanged for months, the fact that they do alter their ai)i)earance has led to the assumiitinn liiat gri'at atmosi)heric

��storms take place on Jiqiiter.

Occasionally Jupiter's belts appear spotted. Just what these spots are, no one knows definitely.

It was in 1878 that the great, mysteri- ous Red Spot of Jupiter, which has puzzled astronomers for many years, was first observed at Brussels by 'SI. Niesten. It was 30,000 miles long one way and over 8,000 miles another. The Earth might figuratively have been dropped' into the Red Spot without touching the sides.

For three years, the Great Red Spot was a constant object of study. It completed its circuit about Jupiter in nine hours, fifty-five minutes and thirty-six seconds.

What is the Great Red Spot? A volcano, said some. That is impossible, because it floats freely. It has a strange effect on its surroundings; it has the property of excavating them, as it were. There is a deep bay in which the spot, rather dim now, is located.

In describing the drawing appearing on the opposite page, Mr. Scriven Bolton, the English astronomer who made it says:

"It is propounded th.it our earth, when once in a plastic condition, rotated on its axis so swiftly that the matter at the equator could not adhere together, and a • breach caused a portion to be fractured, which portion gradually separated from the parent planet. So, apparently, in the case of our cousin-planet Jupiter, whose rota- tional velocity at its surface is as great as ours used to be, there is at present a phe- nomenon which suggests an epoch in the evolution of moon-making. That puzzling object on the surface, known as the t'.reat Red Spot, is not a fixture of the Surface, or we miglu regard it |)urcly as a volcanic vent emitting hot vapors. Its constituent proper- ties have never been ascertained. ... It moves round with the planet's axial rotation. This is especially notewortliy from the fact that theory tells us thai our moon, in its early stages of evolution, was carried round with the earth's axial motion, all the while just grazing the surface, and that its distance therefrom increased through countless ages, and is increasing. The in- ference denotes a Jovian moon in embryo."

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