Part 16 (1/2)
CHAPTER x.x.xIII
THE Ca.n.a.lS OF MARS
Then there are the so-called ca.n.a.ls of Mars, about which so much is written and relatively little known. Faint markings which resemble them in character were first drawn in 1840 and later in 1864, but Schiaparelli, the famous Italian astronomer, is probably their original discoverer, when Mars was at its least distance from the earth in 1877.
He made the first accurate detailed map of Mars at this time, and most of the important or more conspicuous ca.n.a.ls (_ca.n.a.li_, he called them in Italian, that is, channels merely, without any reference whatever to their being watercourses) were accurately charted by him.
At all the subsequent close approaches of Mars, the ca.n.a.ls have been critically studied by a wide range of astronomical observers, and their conclusions as to the nature and visibility of the ca.n.a.ls have been equally wide and varied. The most favorable oppositions have occurred in 1892 and 1894, also in 1907 and 1909. On these occasions a close minimum distance of Mars was reached, that is, about 35 millions of miles; but in 1924 the planet makes the closest approach in a period of nearly a thousand years. Its distance will not much exceed 34 millions of miles.
But although this is a minimum distance for Mars, it must not be forgotten that it is a really vast distance, absolutely speaking; it is something like 150 times greater than the distance of the moon. With no telescopic power at our command could we possibly see anything on the moon of the size of the largest buildings or other works of human intelligence; so that we seem forever barred from detecting anything of the sort on Mars.
Nevertheless, the closest scrutiny of the ruddy planet by observers of great enthusiasm and intelligence, coupled with imagination and persistence, have built up a system of ca.n.a.ls on Mars, covering the surface of the planet like spider webs over a printed page, crossing each other at intersecting spots known as ”lakes,” and embodying a wealth of detail which challenges criticism and explanation.
To see the ca.n.a.ls at all requires a favorable presentation of Mars, a steady atmosphere and a perfect telescope, with a trained eye behind it.
Not even then are they sure to be visible. The training of the eye has no doubt much to do with it. So photography has been called in, and very excellent pictures of Mars have already been taken, some nearly half as large as a dime, showing plainly the lights and shades of the grander divisions of the Martian surface, but only in a few instances revealing the actual ca.n.a.ls more unmistakably than they are seen at the eyepiece.
The appearance and degree of visibility of the ca.n.a.ls are variable: possibly clouds temporarily obscure them. But there is a certain capriciousness about their visibility that is little understood. In consequence of the changing physical aspects, as to season, on Mars and his...o...b..tal position with reference to the earth, some of the ca.n.a.ls remain for a long time invisible, adding to the intricacy of the puzzle.
For the most part the ca.n.a.ls are straight in their course and do not swerve much from a great circle on the planet. But their lengths are very different, some as short as 250 miles, some as long as 4,000 miles; and they often join one another like spokes in the hub of a wheel, though at various angles. As depicted by Lowell and his corps of observers at Flagstaff, Arizona, the ca.n.a.l system is a truly marvelous network of fine darkish stripes. Their color is represented as a bluish green.
Each marking maintains its own breadth throughout its entire length, but the breadth of all the ca.n.a.ls is by no means the same: the narrowest are perhaps fifteen to twenty miles wide, and the broadest probably ten times that. At least that must be the breadth of the Nilosyrtis, which is generally regarded as the most conspicuous of all the ca.n.a.ls. The Lowell Observatory has outstripped all others in the number of ca.n.a.ls seen and charted, now about 500.
What may be the true significance of this remarkable system of markings it is impossible to conclude at present. Schiaparelli from his long and critical study of them, their changes of width and color, was led to think that they may be a veritable hydrographic system for distributing the liquid from the melting polar snows. In this case it would be difficult to escape the conviction that the ca.n.a.ls have, at least in part, been designed and executed with a definite end in view.
Lowell went even farther and built upon their behavior an elaborate theory of life on the planet, with intelligent beings constructing and opening new ca.n.a.ls on Mars at the present epoch. Pickering propounded the theory that the ca.n.a.ls are not water-bearing channels at all, but that they are due to vegetation, starting in the spring when first seen and vitalized by the progress of the season poleward, the intensity of color of the vegetation coinciding with the progress of the season as we observe it.
Extensive irrigation schemes for conducting agricultural operations on a large scale seem a very plausible explanation of the ca.n.a.ls, especially if we regard Mars as a world farther advanced in its life history than our own. Erosion may have worn the continents down to their minimum elevation, rendering artificial waterways not difficult to build; while with the vanis.h.i.+ng Martian atmosphere and absence of rains, the necessity of water for the support of animal and vegetal life could only be met by conducting it in artificial channels from one region of the planet to another.
Interesting as this speculative interpretation is, however, we cannot pa.s.s by the fact that many competent astronomers with excellent instruments finely located have been unable to see the ca.n.a.ls, and therefore think the astronomers who do see them are deceived in some way. Also many other astronomers, perhaps on insufficient grounds, deny their existence _in toto_.
Many patient years of labor would be required to consult all the literature of investigation of the planet Mars, but much of the detail has been critically embodied in maps at different epochs, by Kayser, Proctor, Green, and Dreyer. And Flammarion in two cla.s.sic volumes on Mars has presented all the observations from the earliest time, together with his own interpretation of them. Areography is a term sometimes applied to a description of the surface of Mars, and it is scarcely an exaggeration to say that areography is now better known than the geography of immense tracts of the earth.
For some reason well recognized, though not at all well understood, Mars although the nearest of all the planets, Venus alone excepted, is an object by no means easy to observe with the telescope. Possibly its unusual tint has something to do with this. With an ordinary opera gla.s.s examine the moon very closely, and try to settle precise markings, colors, and the nature of objects on her surface; Mars under the best conditions, scrutinized with our largest and best telescope, presents a problem of about the same order of difficulty. There are delicate and changing local colors that add much uncertainty. Nevertheless, the planet's leading features are well made out, and their stability since the time of the earliest observers leaves no room to doubt their reality as parts of a permanent planetary crust.
The border of the Martian disk is brighter than the interior, but this brightness is far from uniform. Variations in the color of the markings often depend on the planet's turning round on its axis, and the relation of the surface to our angle of vision. If we keep in mind these obstacles to perfect vision in our own day, it is easy to see why the early users of very imperfect telescopes failed to see very much, and were misled by much that they thought they saw. Then, too, they had to contend, as we do, with unsteadiness of atmosphere, which is least troublesome near the zenith.
As their telescopes were all located in the northern hemisphere, the northern hemisphere of Mars is the one best circ.u.mstanced for their investigation; because at the remote oppositions of Mars, which always happen in our northern winter with the planet in high north declination, it is always the north pole of Mars which is presented to our view.
Whereas the close oppositions of the planet always come in our northern midsummer, with Mars in south declination and therefore pa.s.sing through the zenith of places in corresponding south lat.i.tude.
With Mars near opposition, high up from the horizon, a fairly steady atmosphere, and a magnifying power of at least 200 diameters, even the most casual observer could not fail to notice the striking difference in brightness of the two hemispheres: the northern chiefly bright and the southern markedly dark. Formerly this was thought to indicate that the southern hemisphere of Mars was chiefly water and the northern land, much as is the case on the earth: with this difference, however, that water and land on the earth are proportioned about as eleven to four.
But Mars in its general topography presents no a.n.a.logy with the present relation of land and water on the earth. There seems no reason to doubt that the northern regions with their prevailing orange tint, in some places a dark red and in others fading to yellow and white, are really continental in character. Other vast regions of the Martian surface are possibly marshy, the varying depth of water causing the diversity of color. If we could ever catch a reflection of sunlight from any part of the surface of Mars, we might conclude that deep water exists on the planet; but the farther research progresses, the more complete becomes the evidence that permanent water areas on Mars, if they exist at all, are extremely limited.
Since 1877 Mars has been known to possess two satellites, which were discovered in August of that year by Hall at Was.h.i.+ngton. Moons of this planet had long been suspected to exist and on one or two previous occasions critically looked for, though without success. In the writings of Dean Swift there is a fanciful allusion to the two moons of Mars; and if astronomers had chanced to give serious attention to this, Phobos and Deimos, as Hall named them, might have been discovered long before.
They are very small bodies, not only faint in the telescope, but actually of only ten or twenty miles diameter; and from the strange relation that Phobos, the inner moon, moves round Mars three times while the planet itself is turning round only once on its axis, some astronomers incline to the hypothesis that this moon at least was never part of Mars itself, but that it was originally an inner or very eccentric member of the asteroid group, which ventured within the sphere of gravitation of Mars, was captured by that planet, and has ever since been tributary to it as a secondary body or satellite.
CHAPTER x.x.xIV