Amid the seemingly countless stars that on a clear night spangle the vast dome overhead, there appeared last autumn to be a new-comer, a very large and ruddy one, that rose at sunset through the haze about the horizon. That star was the planet Mars, so conspicuous when in such position as often to be taken for a portent. Large as he then looked, however, he is in truth but a secondary planet traveling round a secondary sun; but his interest for us is out of all proportion to his actual size or his relative importance in the cosmos. For that sun is our own; and that planet is, with the exception of the moon, our next to nearest neighbor in space, Venus alone ever approaching us closer. From him, therefore, of all the heavenly bodies, may we expect first to learn something beyond celestial mechanics, beyond even celestial chemistry; something in answer to the mute query that man instinctively makes as he gazes at the stars, whether there be life in worlds other than his own.
Hitherto the question has received no affirmative reply, although the trend of all latter-day investigation has been to such affirmation; for science has been demonstrating more and more clearly the essential oneness of the universe. Matter proves to be common property. We have learnt that the very same substances with which we are familiar on this our earth, iron, magnesium, calcium, and the rest, are present in the far-off stars that strew the depths of space. Nothing new under the sun! Indeed, there is nothing new above it but ever-varying detail. So much for matter. As for mind beyond the confines of our tiny globe, modesty, backed by a probability little short of demonstration, forbids the thought that we are the sole thinkers in this great universe.
That we are the only minds in space it takes indeed a very small mind to fancy. Our relative insignificance commonly escapes us. If we reduce the universe to a scale on which we can conceive it, that on which the earth shall be represented by a good-sized pea, with a grain of mustard seed, the moon, circling about it at a diameter of seven inches, the sun would be a globe two feet in diameter, two hundred and twenty feet away. Mars, a much smaller pea, would circle round the two-foot globe, three hundred and fifty feet from its surface; Jupiter, an orange, at a distance of a quarter of a mile; Saturn, a small orange, at two fifths of a mile; and Uranus and Neptune, good-sized plums, three quarters of a mile and a mile and a quarter away, respectively. The nearest star would lie two hundred and fifty thousand miles off, or at about the actual distance of our own moon, and the other stars at corresponding distances beyond that; that is, on a scale upon which the moon should be but seven inches off, the nearest star would still be as far from us as the moon is now. When we think that each of these stars is probably the centre of a solar system on a grander scale than our own, we cannot seriously take ourselves to be the only minds in the universe.
But improbable as the absence of ultra-terrestrial life in a general way is, up to the present time we have no proof of its particular existence in worlds beyond our own. Whether the observations I am now to describe have revealed something on the point I shall leave the reader to himself to judge, after laying the facts before him; for it is with this in view that the present papers will deal with Mars, since any answer on this point is the most generally interesting outcome of a study of the planet. That the observations also disclose the fact that the hitherto accepted period of its rotation proves to be too small by the hundredth of a second is a matter of far greater moment, of course, but one which leaves the average man comparatively cool. That Mars, however, should be peopled by intelligent beings, although physically they be utterly unlike us, more goblins than men or animals, is a suggestion which appeals romantically, at least, to everybody.
To determine whether a planet be the abode of life, two questions about it must be answered in turn: first, are its physical conditions such as to render it habitable? And secondly, are there any signs of its actual habitation? Unless we can answer the first point satisfactorily, it were futile to seek for evidence of the second.
Of such planets as doubtless circle round other suns we as yet know nothing. Our search is perforce confined at present to the members of our own solar family. Now, when we first scan them for answer to our first query, we find but two that promise even the possibility of an affirmative reply, Mars and Venus. All the others turn out, upon scrutiny, to lie beyond the pale, either because they are too little; for, curiously enough, mere size settles the matter.
The giant Jupiter piques inquiry first by showing us great cloud-belts that recall our own equatorial and temperate cloud-zones. But further study discloses that his clouds are in kind quite unlike those of our earth. Neither the hour of his day nor the season of his year brings change in them. They slowly, very slowly, alter in appearance, indeed, but not in obedience to that central ruler that gathers and dispels our own. In short, the Jovian clouds are not sun-raised, but self-raised ones. It is heat inherent in Jupiter himself, not heat from the sun, that belts him about with his great girdles of cloud. We can even see, in all probability, his glowing inner self; for Jupiter shows brick-red between his belts, like a molten mass.
The same state of things is yet more strikingly instanced by Saturn; for the tilt of Saturn's pole is not very unlike that of the earth, and in consequence his equatorial regions are at times raised far above the plane of his orbit; at others, dipped far below it. Yet unlike the earth's cloud-belts, his never travel northward when the sun goes north, nor follow the sun when he journeys south again. So far as the sun is concerned, the Saturnian cloud-belts are invariable. Like the Jovian, they owe their formation to the planet's own heat. Like Jupiter, too, Saturn, shows red beneath. From all this it is pretty plain that the giant planets are far from pleasurable abodes, as yet midway in evolution between actual suns and tenantable worlds; too cooled down for the one state, and not yet cooled down enough for the other.
Uranus and Neptune give evidence, also, of being in a chaotic condition, orbs informe, ingens, cui lumen ademptum,—no longer suns, but as yet quite unfit to support beings even distantly analogous to ourselves.
With Mercury littleness is even more fatal to life; for though the giant planets may perhaps, at some future day, grow to be life-supporting, a small one apparently never was, nor ever can be, peopled by beings in the least resembling us. Incapacity to quarter folk is included in the more general incapacity to hold an atmosphere; for absence of atmosphere precludes the possibility of life as we know it. That a planet may be too small to have an atmospheric envelope we shall see more definitely later. That life, however, of a type of which we have no conception may not exist in all these orbs we must be wary of stating, for nothing is more dangerous than a general denial, except a particular statement.
We are limited, therefore, in our present inquiry, to Venus and Mars. But Venus, contrary to her name, proves provokingly modest, the most modest of all the company of heaven, keeping herself so constantly veiled in cloud that we seldom, if ever, are permitted to a peep at her actual surface. In consequence, beyond the fact that she has an atmosphere of considerable though not excessive density, we know little about her.
With Mars, on the other hand, no such false modesty balks us at the outset. The planet named after the old God of War—satirically, it would seem, since he turns out to present characteristics quite the reverse of warlike—lets himself be seen as well as thirty-five millions of miles of separation will allow.
Now, to all forms of life of which we have any conception, two things in nature are vital, air and water. A planet must possess these two things to be able to support any life at all upon its surface. Some articles that we might deem essential to well-being fall cosmically under the head of luxuries; but air and water are necessities of existence. There is no creature which is not in some measure dependent upon both of them. How then is Mars off for air?
Fortunately for an answer to this question, air is as vital to change in the inorganic processes of nature as it is to those other changes which we call peculiarly life. Atmosphere is essential not only to life upon a planet, but to the production of any change whatever upon that planet's surface. Without it, not only development, but decay would come to a standstill, when once all that was friable land crumbled to pieces under the alternate roasting and refrigerating to which the planet's surface would be exposed as it revolved upon its axis toward and away from the sun. Disintegration once effected, the planet would roll, a mummy world, through space. Since atmosphere, therefore, is a sine qua non to any change upon a planet's surface is proof positive of the presence of an atmosphere, however incapable of detection such atmosphere be by direct means.
Now changes take place upon the surface of Mars, changes vast enough to be visible from the earth. When properly observed they turn out to be most marked. We will begin with the look of the planet last June. Its general aspect then was tripartite. Upon the top part of the disc, round what we know to be the planet's pole, appeared a great white cap, the south polar cap. The south lay at the top, because all astronomical views are, for optical reasons, upside down; but inasmuch as we never see the features otherwise, to have them right side up is not vital to the effect. Below the white cap lay a region chiefly bluish-green, interspersed, however, with portions more or less reddish-ochre. Below this, again, came a vast reddish-ochre stretch, the great continental deserts of the planet.