The Trouvelot astronomical drawings manual

by E. L. Trouvelot

On the opposite hemisphere to that represented on Plate VIII., the white fringes bordering the dark spots are much more conspicuous than they are on this side. On the eastern side of a remarkable dark spot called Kaiser Sea, they are very bright, and almost always present, although they vary considerably, both in brightness and in extent. To the south of Kaiser Sea, they are very conspicuous on the eastern border of Lockyer Land, forming an elevated and deeply indented coast-line along Lambert Sea. There the white spots never disappear entirely, being always visible on the north side, where they turn westward along Dawes' Ocean—the mountain chain attaining there its greatest altitude. Very frequently Lockyer Land, which seems to be a vast plateau, appears throughout white and brilliant, this occurring usually towards the sunrise or sunset of that region, probably from the condensation of vapors and the formation of fogs, but generally this whiteness gradually disappears with the progress of the sun above this plateau. Inside of the great continents of Mars these temporary white spots are not so frequent, but when visible they occupy always the same positions—a fact which probably indicates that they occupy the culminating points of these continents. One of these temporary white spots inside of the continents is represented on Plate VIII., on the left-hand side, below De La Rue Ocean, on Maedler Continent.

Although large, opaque, cumulus-shaped, cloud-like forms are seen in the polar regions of Mars, such forms are very seldom seen in the tropical zones, or, at least, it appears so, from the fact that my observations, continued during the last seven years, have disclosed no real opaque cloudy forms there. Although the Martial sky is frequently overcast by dense vapors or thick fogs in these regions, yet no real opaque clouds were ever seen; the most prominent among the dusky spots being faintly visible through the vapory veil, when they approached the centre of the disk.

Besides these phenomena, which prove that Mars is surrounded by an atmosphere having a great deal of similarity to our own, a further proof is afforded by the fact that the dark spots, which appear sharply defined and black when they are seen near the centre, become less and less visible as they advance towards the limb, and are totally invisible before they reach it. Moreover, the spectroscope also indicates the existence of an atmosphere, and even the presence of watery vapor in it. A very curious state of the Martial atmosphere is revealed by my observations of 1877-78. During eight consecutive weeks, from December 12th to February 6th, a whole hemisphere of the planet—precisely that represented on Plate VIII.—was completely covered by dense vapors, or a thick fog which barely allowed the dark spots to be seen through it, even when they were in the centre of the disk. The opposite hemisphere of Mars appeared just as clear and calm as possible; there all the spots and their minutest details could be seen, and when the planet was observed at the proper time, the line separating the foggy from the clear side was plainly visible.

The reddish tint observed on the continents of Mars has been supposed by some astronomers to be the real color of the atmosphere of this planet. But, for many reasons, this explanation is not acceptable. Besides the fact that the border of the planet appears white, while it should be more red than the other part, owing to the greater depth of atmosphere there presented to us, the polar spots, the white bands along the sea-coasts, and the cloud-like forms appear perfectly white, not the slightest tint of red being visible on them, as would be the case if these objects were seen through an atmosphere tinted red. Other astronomers have supposed that the vegetation of this planet has a reddish color; but this is not supported by observation. It has been again supposed, with much more probability, that the surface of Mars is composed of an ochreous material which gives the planet its predominant ruddy color.

Until lately Mars was supposed to be without a satellite, but in August, 1877, Professor Hall, of the Washington Observatory, made one of the most remarkable discoveries of the time, and found two satellites revolving around this planet. These satellites are among the smallest known heavenly bodies, their diameter having been estimated at from 6 to 10 miles for the outer satellite, and from 10 to 40 miles for the inner one.

The most extraordinary feature of these bodies is the proximity of the inner satellite to the planet, and the consequent rapidity of its motion. The distance of the inner satellite from the centre of Mars is about 6,000 miles, and from surface to surface it is less than 4,000 miles, or a little more than the distance from New York to San Francisco. The shortest period of revolution of any satellite previously known, is that of the inner satellite of Saturn, which is a little more than 22½ hours; but the inner satellite of Mars accomplishes its revolution in 7h. 38m., or in 17 hours less than the period of rotation of the planet upon its axis. The period of revolution of the outer satellite is greater, of course, and equals 30h. 7m.

From this rapidity of motion of the inner satellite of Mars, a very curious result follows, which at first sight may appear in contradiction with the fact that this body has a direct motion, like that of all the planets of the solar system, and moves around Mars from west to east. While the outer satellite of this planet, in company with all the stars and planets, rises in the east and sets in the west, the inner satellite, on the contrary, rises in the west and sets in the east. Since the period of rotation of Mars is greater than is the period of revolution of this satellite, it necessarily follows that this last body must constantly be gaining on the rotation, and, consequently, that the satellite sets in the east and rises in the west, compassing the whole heavens around Mars three times a day, passing through all its phases in 11 hours, each quarter of this singular Moon lasting less than 3 hours.

It has been shown above that Mars has many points of resemblance to the Earth. It has an atmosphere constituted very nearly like ours; it has fogs, clouds, rains, snows, and winds. It has water, or at least some liquids resembling it; it has rivers, lakes, seas and oceans. It has also islands, peninsulas, continents, mountains and valleys. It has two Moons, which must create great and rapid tides in the waters of its seas and oceans. It has its days and nights, its warm and cold seasons, and very likely its vegetation, its prairies and forests, like the Earth. On the other hand, its year and seasons are double those of the Earth, and its distance from the Sun is greater.

Is this planet, which is certainly constituted very nearly like our globe, and seems so nearly fitted for the wants of the human race, inhabited by animals and intelligent beings?

To answer this question, either in the negative or in the affirmative, would be to step out of the pure province of science, and enter the boundless domain of speculation, since no observer has ever seen anything indicating that animal life exists on Mars, or on any other planet or satellite. So far as observation goes, Mars seems to be a planet well suited to sustain animal life, and we may reason from analogy that if animal life can exist at all outside of the Earth, Mars must have its flora and fauna; it must have its fishes and birds, its mammalia and men; although all these living beings must inevitably be very different in appearance from their representatives on the Earth, as can easily be imagined from the differences existing between the two planets. Although all this is possible, and even very probable, yet it must be remembered that we have not the slightest evidence that it is so; and until we have acquired this evidence, we may only provisionally accept this idea as a pleasing hypothesis, which, after all, may be wrong and totally unfounded.