Other Worlds / Their Nature, Possibilities and Habitability in the Light of the Latest Discoveries

by Garrett Putman Serviss

All this variety of tone and color makes of a telescopic view of Jupiter a picture that will not quickly fade from the memory; while if an instrument of considerable power is used, so that the wonderful details of the belts, with their scalloped edges, their diagonal filaments, their many divisions, and their curious light and dark spots, are made plain, the observer is deeply impressed with the strangeness of the spectacle, and the more so as he reflects upon the enormous real magnitude of that which is spread before his eye. The whole earth flattened out would be but a small blotch on that gigantic disk!

Then, the visible rotation of the great Jovian globe, whose effects become evident to a practised eye after but a few minutes' watching, heightens the impression. And the presence of the four satellites, whose motions in their orbits are also evident, through the change in their positions, during the course of a single not prolonged observation, adds its influence to the effectiveness of the scene. Indeed, color and motion are so conspicuous in the immense spectacle presented by Jupiter that they impart to it a powerful suggestion of life, which the mind does not readily divest itself of when compelled to face the evidence that Jupiter is as widely different from the earth, and as diametrically opposed to lifelike conditions, as we comprehend them, as a planet possibly could be.

The great belts lie in latitudes about corresponding to those in which the trade-winds blow upon the earth, and it has often been suggested that their existence indicates a similarity between the atmospheric circulation of Jupiter and that of the world in which we live. No doubt there are times when the earth, seen with a telescope from a distant planet, would present a belted appearance somewhat resembling that of Jupiter, but there would almost certainly be no similar display of colors in the clouds, and the latter would exhibit no such persistence in general form and position as characterizes those of Jupiter. Our clouds are formed by the action of the sun, producing evaporation of water; on Jupiter, whose mean distance from the sun is more than five times as great as ours, the intensity of the solar rays is reduced to less than one twenty-fifth part of their intensity on the earth, so that the evaporation can not be equally active there, and the tendency to form aerial currents and great systems of winds must be proportionally slight. In brief, the clouds of Jupiter are probably of an entirely different origin from that of terrestrial clouds, and rather resemble the chaotic masses of vapor that enveloped the earth when it was still in a seminebulous condition, and before its crust had formed.

Although the strongest features of the disk of Jupiter are the great cloud belts, and the white or colored spots in the equatorial zone, yet the telescope shows many markings north and south of the belts, including a number of narrower and fainter belts, and small light or dark spots. None of them is absolutely fixed in position with reference to others. In other words, all of the spots, belts, and markings shift their places to a perceptible extent, the changes being generally very slow and regular, but occasionally quite rapid. The main belts never entirely disappear, and never depart very far from their mean positions with respect to the equator, but the smaller belts toward the north and south are more or less evanescent. Round or oblong spots, as distinguished from belts, are still more variable and transient. The main belts themselves show great internal commotion, frequently splitting up, through a considerable part of their length, and sometimes apparently throwing out projections into the lighter equatorial zone, which occasionally resemble bridges, diagonally spanning the broad space between the belts.

JUPITER AS SEEN AT THE LICK OBSERVATORY IN 1889. THE GREAT RED SPOT IS VISIBLE, TOGETHER WITH THE INDENTATION IN THE SOUTH BELT.

Perhaps the most puzzling phenomenon that has ever made its appearance on Jupiter is the celebrated "great red spot," which was first noticed in 1878, although it has since been shown to be probably identical with a similar spot seen in 1869, and possibly with one noticed in 1857. This spot, soon after its discovery in 1878, became a clearly defined red oval, lying near the southern edge of the south belt in latitude about 30°. Its length was nearly one third of the diameter of the disk and its width almost one quarter as great as its length. Translated into terrestrial measure, it was about 30,000 miles long and 7,000 miles broad.

In 1879 it seemed to deepen in color until it became a truly wonderful object, its redness of hue irresistibly suggesting the idea that it was something hot and glowing. During the following years it underwent various changes of appearance, now fading almost to invisibility and now brightening again, but without ever completely vanishing, and it is still (1901) faintly visible.

Nobody has yet suggested an altogether probable and acceptable theory as to its nature. Some have said that it might be a part of the red-hot crust of the planet elevated above the level of the clouds; others that its appearance might be due to the clearing off of the clouds above a heated region of the globe beneath, rendering the latter visible through the opening; others that it was perhaps a mass of smoke and vapor ejected from a gigantic volcano, or from the vents covering a broad area of volcanic action; others that it might be a vast incandescent slag floating upon the molten globe of the planet and visible through, or above, the enveloping clouds; and others have thought that it could be nothing but a cloud among clouds, differing, for unknown reasons, in composition and cohesion from its surroundings. All of these hypotheses except the last imply the existence, just beneath the visible cloud shell, of a more or less stable and continuous surface, either solid or liquid.