 | Mars |  |
MARS.
II. THE WATER PROBLEM.
AFTER air, water. If Mars be capable of supporting life, there must be water upon his surface; for to all forms of life water is as vital a matter as air. To all organisms water is absolutely essential. On the question of habitability, therefore, it becomes all-important to know whether there be water on Mars.
Any one looking through a telescope at the planet, early last summer, would at once have been struck by the fact that its surface was diversified by markings in three colors,—white, blue-green, and reddish-ochre; the white lying in a great oval at the top of the disc. The white oval was the south polar ice-cap. In this polar cap our water problem takes its rise.
On the 31st of May, 1894, the south polar cap stretched, practically one unbroken waste of ice, over about fifty degrees of latitude; that is, it covered nearly the whole frigid zone. Although due, in all probability, to successive depositions of frost rather than snow, the result, both in appearance and in behavior, makes striking counterpart to the antarctic ice-sheet of our own earth. Its visible contour was almost perfectly elliptical, showing it to be, in truth, nearly circular. That it was already in active process of melting was evident from its slowly lessening size. It was the most interesting feature on the disc, being peculiarly well placed for observation, owing to the tilt of the polar axis; for the Martian south pole was at the time bowed toward the earth at an angle of 24°, a southern inclination which has not been equaled since 1877. The dip of the pole displayed the snow-cap to great advantage, and enabled the metamorphosis it underwent to be specially well seen.
Through June and July the snows were melting very fast, at the rate of
Practically at the first observation made at Flagstaff in June, there showed, bordering the edge of the snow, a narrow, dark blue band or ribbon of color encircling the cap. The band varied in width at different places, being widest where the blue-green areas to the north of it were widest, and narrowest where they were narrowest. Its greatest breadth was about two hundred and twenty miles, its least about one hundred. In two places it expanded into great bays, the more prominent of them being just above the largest blue-green area on the disc. That the width of this antarctic girdle was proportionate to the width of the blue-green areas below it is a highly suggestive fact. Both bays were blue, the larger and more striking one especially so, appearing in good seeing of a beautiful cobalt blue, like some Martian grotto of Capri.
Both the band and its bays were contrasted with the blue-green areas contiguous to them, somewhat in tint, but yet more in tone. They were bluer, and distinctly darker. This hinted at a difference of constitution, which hint was emphasized by the action of the band; for as the snow shrank back toward the pole the blue belt followed it, keeping pace with its retreat. Instead of remaining in the place where it had first appeared, as it must have done had it been a permanent marking upon the surface of the planet, it withdrew steadily southward, so as always to border the melting snow.
At about the same time a rift made its appearance in the midst of the ice-cap. On June 9, when on the meridian early in the morning it looked like a huge cart-track coming down toward one through the snow. It proved to be three hundred and fifty miles wide, and debouched into the dark encircling band. A second narrower rift ran into it near the centre of the cap.
On the same morning, about half past five o'clock, starlike points suddenly shone out upon the snow, between the great bay and the first rift. After shining there for a few minutes they as suddenly vanished. It is evident what these were,—not fabled flash-lights of the Martians, but the glint of snow-slopes tilted at just the angle to reflect the sun toward the earth. On subsequent mornings others appeared, not so brilliant, the position of the planet with regard to the earth having slightly shifted in the mean time. There is something romantic in the thought of these far-off glistens from other-world antarctic snows, and in the sight there is corroboration of the snow's character.
As the Martian spring progressed, the rifts spread, until at last they cut the ice-cap in two. The smaller portion then proceeded to disappear, while the larger shrank correspondingly in size. The relative times of disappearance of different parts of the cap give us some information about the relative elevations and depressions of the south circumpolar regions. In consequence, I have been able to construct a contour map of these polar portions of the planet. There are advantages in thus conducting polar expeditions astronomically. One not only lives like a civilized being through it all, but he brings back something of the knowledge he went out to acquire.
There has even been vouchsafed the realization of that dream of explorers, an open polar sea; for as the first rift widened, Professor W. H. Pickering marked a large lake develop in the midst
As the snows dwindled in size, the blue band about them shrank to correspond. By August it was a barely discernible thread drawn round the tiny white patch which was all that remained of the enormous snow-fields of some months before. Finally, on October 13, the snow entirely disappeared, and the spot where it and its girdle, long since grown too small for detection, had been became one yellow stretch.
That the blue was water at the edge of the melting snow seems unquestionable. That it was of the color of water, that it so persistently bordered the melting snow, and that it subsequently vanished are three facts mutually confirmatory of this deduction. Professor W. H. Pickering made the polariscope tell the same tale; for, on scrutinizing the great bay through it, he found the light coming from the bay to be polarized. Now, to polarize the light it reflects is a property, as we know, of a water surface.
From all this we may conclude that we have here a polar sea, a real body of water. There is, therefore, water on the surface of Mars. We also mark that this body of water is ephemeral. It exists while the snow-cap is melting, and then it somehow vanishes. What becomes of it, and whether there be other bodies of water on the planet, either permanent or temporary, we shall now go on to inquire.
While it existed in any size, the polar sea was bordered on the north, all the way round and during all the time it was visible, by blue-green areas. These blue-green areas were strewn with several more or less bright regions, while below them came the great reddish-ochre stretches of the disc. Now, the blue-green areas have generally been considered to be seas, just as the reddish-ochre regions have been held to be land. That the latter are land there is very little doubt; not only land, but nothing but land,—land very pure and simple; that is, deserts. For they behave just as deserts should behave, chiefly by not behaving at all; remaining, except for certain phenomena to be specified later, unchangeable.
With the so-called seas, however, the case is different. Several important facts conspire to throw grave doubt, and worse, upon their aquatic character. To begin with, they are of every grade of tint,—a very curious feature for seas to exhibit, unless they were everywhere but a few feet deep; which again is a most singular characteristic for seas that cover hundreds of thousands of square miles in extent,—seas, that is, as big as the Bay of Bengal. The Martian surface would have to be amazingly flat for this to be possible. We know it to be relatively flat, but to be as flat as all this would seem to pass the bounds of credible simplicity. Here also Professor W. H. Pickering's polariscope investigations come in with effect, for he found the light from the supposed seas to show no trace of polarization. Hence these were probably not water.
In parenthesis we may here take notice of the absence of a certain phenomenon whose presence, apparently, should follow upon water surfaces such as the so-called seas would offer us. Although its absence is not perhaps definitive as to their marine character, it is certainly curious, and worth nothing. If a planet were covered by a sheet of water, that water surface would, mirror-like, reflect the sun in one more or less definite spot. Looked at from a distance, this spot would, were it bright enough, be seen as a high light on the dark background of the ocean about it. It would seem to be a fixed star at a certain point on the disc, the surface features rotating under it. The necessary position is easily calculated, and this shows that parts of the so-
Not only do different parts of the so-called seas contrast in tint with one another, but the same part of the same sea varies in tint at different times. Schiaparelli noticed that, at successive oppositions, the same sea showed different degrees of darkness, and he suggested that the change in tone was dependent in some way upon the Martian seasons.
Observations at Flagstaff have demonstrated this to be the case, for it has been possible to see the tints occur consecutively. In consequence, we know not only that changes take place on the surface of Mars other than in the polar cap, and very conspicuous ones too, but that these are due to the changing seasons of the planet's year. We will now see what they look like.
To the transubstantiation of changes of the sort it is a prime essential that the drawings from whose comparison the contrast appears should all have been made by the same person, at the same telescope, under as nearly as possible the same atmospheric conditions, since otherwise the personal equation of the observer, the impersonal inequalities of instruments, and the special atmosphere of the station play so large a part in the result as to mask that other factor in the case, any change in the planet itself. How easily this masking is accomplished appears from drawings made by different observers of the same Martian features at substantially the same moment. Several interesting specimens of such personal peculiarities may be seen by the curious in Flammarion's admirable thesaurus, La Planete Mars. In some of these likenesses of the planet it is pretty certain that Mars would never recognize himself.
To have drawings simply swear at one another across a page is, in the interests of deduction, objectionable. For their testimony to be worth having they must agree to differ. If, therefore, Mars is to be many, his draughtsman must be one. So much, at least, is fulfilled by the drawings in which the changes now to be described are recorded; for they were all made by me, at the same instrument, under the same general atmospheric conditions. As the same personality enters all of them, it stands, as between them, eliminated from all, to increased certainty of deduction. Since, furthermore, the drawings were all made in the months preceding and following one opposition, change due to secular variation is reduced to a minimum. As a matter of fact, the changes are such as to betray their own seasonal character. They constitute a kinematical as opposed to a statical study of the planet's surface.
The changes are much more evident than might be supposed. Indeed, they are quite unmistakable. As for their importance, it need only be said that that deduction from them furnishes, in the first place, strong inference that Mars is a living world, subject to an annual cycle of surface growth, activity, and decay; and shows, in the second place, that this Martian yearly round of life must differ in certain interesting particulars from that which forms our terrestrial experience. The phenomena evidently make part of a definite chain of changes of annual development. So consecutive, and, in their broad characteristics, apparently so regular are these changes that I have been able to find corroboration of what appears to be their general scheme in drawings made at previous oppositions. In consequence, I
The changes in appearance now to be chronicled refer, not to the melting of the polar snows, except as such melting forms the necessary preliminary to what follows, but to the subsequent changes in look of the surface itself. To their exposition, however, the polar phenomena become inseparable adjuncts, since they are inevitable ancillaries to the result.
With the familiar melting of the snow-cap begins the yearly round of the planet's life. With the melting of our own arctic or antarctic cap might similarly be said to begin the earth's annual activity. But here at the very outset there appears to be one important difference between the two planets. On the earth the relation of the melting of the polar snows to the awakening of surface activity is a case of post hoc simply; on Mars it seems to be a case of propter hoc as well. For, unlike the earth, which has water to spare, and to which, therefore, the unlocking of its polar snows is a matter of no direct economic value, Mars is apparently in straits for the article, and has to draw on its polar reservoir for its annual supply. Upon the melting of its polar cap, and the transference of the water thus annually set free to go its rounds, seem to depend all the seasonal phenomena on the surface of the planet.
The observations upon which this deduction is based extend over a period of nearly six months, from the last day of May to the 22d of November. They cover the regions from the south pole to about latitude forty north. That changes analogous to those recorded, differing, however, in details, occur six Martian months later in the planet's northern hemisphere is proved by what Schiaparelli has seen; for though the general system is, curiously, one for the whole planet, the particular character of different parts of the surface alters the action there to some extent.
For an appreciation of the meaning of the changes, it is to be borne in mind throughout that the vernal equinox of Mars' southern hemisphere occurred on April 17, 1894; the summer solstice of the same hemisphere on August 31; and its autumnal equinox on February 7, 1895.
On the 31st of May, therefore, it was toward the end of April on Mars. The south polar cap was, as we have seen, very large, and the polar sea in proportion. That the polar sea was the darkest and the bluest marking on the disc implies that it was, at all events, the deepest body of water on the planet, whether the other so-called seas were seas or not. This polar sea plays deus ex machina to all that follows.
So soon as the melting of the snow was well under way, long straits, of deeper tint than their surroundings, made their appearance in the midst of the dark areas. I did not see them come, but as I afterward saw them go, it is evident that they must have come. They were already there on the last day of May. The most conspicuous of them lay between Noachis and Hellas, in the Mare Australe. It began in the great polar bay, and thence traversed the Mare Erythraeum to the Hour-Glass Sea (Syrtis Major). The next most conspicuous one started in the other bay, and came down between Hellas and Ausonia. Although these straits were distinguishably darker than the seas through which they passed, the seas themselves were then at their darkest. The fact that these straits traversed the seas suffices to raise a second doubt as to the genuineness of seas; the first suspicion as to their true character
The appearance of things at this initial stage of the Martian Nile-like inundation last June was most destructive to modern maps of Mars, for all the markings between the south polar cap and the continental coast-line seemed with one consent to have as nearly as might be obliterated themselves.
It was impossible to fix any definite boundaries to the south temperate chain of islands, so indistinguishably did the light areas and the dark ones merge into each other. What was still more striking, the curious peninsulas which connect the continent with the chain of islands to the south of it, and form so singular a feature of the planet's geography, were invisible. One continuous belt of blue-green stretched from the Syrtis Major to the Columns of Hercules.
For some time the dark areas continued largely unchanged in appearance; during, that is, the earlier and most extensive melting of the snow-cap. After this their history became one long chronicle of fading out. Their lighter parts grew lighter, and their darker ones less dark. For, to start with, they were made up of many tints; various shades of blue-green interspersed with hints of orange-yellow. The gulfs and bays bordering the continental coast were the darkest of these markings; the long straits between the polar sea and the Syrtis Major were the next deepest in tone.
The first marked sign of change was the reappearance of Hesperia. Whereas in June it had been practically non-existent, by August it had become perfectly visible and in the place where it is usually depicted. In connection with its reappearance two points are to be noted: first, the amount of the change, for Hesperia is a stretch of land over two hundred miles broad by six hundred miles long; and, secondly, the fact that its previous invisibility was not due to any sort of obscuration. The persistent clear-cut character of the neighboring coast-line during the whole transformation showed that nothing in the way of mist or cloud had at any time hidden the peninsula from view. A something was actually there in August which had not been there in June.
As yet nothing could be seen of Atlantis. It was not until the 30th of October that I caught sight of it. About the same time, the straits between the islands, Xanthus, Scamander, Ascanius, and Simois, came out saliently dark, a darkness due to contrast. The line of south temperate islands and their separate identity were then for the first time apparent.
Meanwhile, the history of Hesperia continued to be instructive. From having been absent in June and conspicuous in August, it returned in October to a mid-position of visibility. Vacillating as these fluctuations in appearance may seem at first sight, they were really quite consistent; for they were due to one progressive change in the same direction, a change that was manifested first in Hesperia itself, and then in the regions round about it. From June to August, Hesperia changed from a previous blue-green, indistinguishable from its surroundings, to yellow, the parts adjacent remaining much as before. As a consequence, the peninsula stood out in marked contrast to the still deep blue-green regions by its side. Later, the surroundings themselves faded, and their change had the effect of once more partially obliterating Hesperia.
While Hesperia was thus causing itself to be noticed, the rest of the south temperate zone, as we may call it for identification's sake, was unobtrusively
Certain smaller details of the change that came over the face of the dark regions at the time were as curious as they were marked. For example, the Fastigium Aryn, the tip of the triangular cape which, by jutting out from the continent, forms the forked bay called the Sabaeus Sinus, and which, because of its easy identification, has been selected for the zero meridian of Martian longitudes, began in October to undergo strange metamorphosis. On October 15 it shot out a sort of tail southward. On the 16th this tail could be followed all the way to Deucalionis Regio, to which it made a bridge across from the continent, thus cutting the Sabaeus Sinus completely in two.
Another curious causeway of the same sort made its appearance in November, connecting the promontory known as Hammonis Cornu with Hellas. Both of these necks of orange-ochre were of more or less uniform breadth throughout.
The long, dark streaks that in June had joined the Syrtis Major to the polar sea had nearly disappeared by October; in their southern parts they had vanished completely, and they had very much faded in their northern ones. The same process of fading uncovered certain curious rhomboidal bright areas in the midst of the Syrtis Major.
It will be seen that the extent of these changes was enormous. Their size, indeed, was only second in importance to their character; for it will also have been noticed that the changes were all in one direction. A wholesale transformation of the blue-green regions into orange-ochre ones was in progress upon that other world.
What can explain so general and so consecutive a change in hue? Water suggests itself; for a vast transference of water from the pole to the equator might account for it. But there are facts connected with the change which seem irreconcilable with the idea of water. In the first place, Professor W. H. Pickering found that the light from the great blue-green areas showed no trace of polarization. This tended to strengthen a theory put forth by him some years ago, that the greater part of the blue-green areas are not water, but something which at such a distance would also look blue-green, namely, vegetation. Observations at Flagstaff not only confirm this, but limit the water areas still further; in fact, practically do away with them entirely. Not only do the above polariscopic tests tend to this conclusion, but so does the following observation of mine in October.
Toward the end of October, a strange, and, for observational purposes, a distressing phenomenon took place. What remained of the more southern dark regions showed a desire to vanish, so completely did those regions proceed to fade in tint throughout. This was first noticeable in the Cimmerian Sea, then in the Sea of the Sirens, and in November in the Mare Erythraeum about the Lake of the Sun. The fading steadily progressed until it had advanced so far that in poor seeing the markings were almost imperceptible, and the planet presented a nearly uniform ochre disc.
This was not a case of obscuration; for in the first place it was general, and in the second place the coast-lines were not obliterated. The change, therefore, was not due to clouds or mist.
What was suggestive about the occurrence was that it was unaccompanied by a corresponding increase of blue-green elsewhere. It was not simply that portions of the planet's surface changed tint, but that, taking the disc in its entirety, the whole amount of the blue-green upon it had diminished, and that
If the blue-green color was due to water, where had all the water gone? Nowhere on the visible parts of the planet; that is certain. Nor could it very well have gone to those north circumpolar regions hid from view by the tilt of the disc; for there was no sign of a growing north polar cap, and, furthermore, Schiaparelli's observations upon that cap show that there should not have been. As we saw in the last paper, he found that it developed late, apparently one month or so after the vernal equinox of its hemisphere, whereas at the time the above change occurred it was not long after that hemisphere's winter solstice.
But if, instead of being due to water, the blue-green tint had been due to leaves and grasses, just such a fading out as was observed should have taken place as autumn came on, and that without proportionate increase of green elsewhere; for the great continental areas, being desert, are incapable of supporting vegetation, and therefore of turning green.
There is thus reason to believe that the blue-green regions of Mars are not water, but, generally at least, areas of vegetation; from which it follows that Mars is very badly off for water, and that the planet is dependent on the melting of its polar snows for practically its whole supply.
Such scarcity of water on Mars is just what theory would lead us to expect. Mars is a smaller planet than the earth, and therefore is relatively more advanced in his evolutionary career. He is older in age, if not in years; for whether his birth as a separate world antedated ours or not, his smaller size, by causing him to cool more quickly, would necessarily age him faster. But as a planet grows old, its oceans, in all probability, dry up, the water retreating through cracks and caverns into its interior. Water thus disappears from its surface, to say nothing of what is being continually imprisoned by chemical combination. Signs of having thus parted with its oceans we see in the case of the moon, whose so-called seas were probably seas in their day, but have now become old sea-bottoms. On Mars the same process is going on, but would seem not yet to have progressed so far, the seas there being midway in their career from real seas to arid depressed deserts; no longer water surfaces, they are still the lowest portions of the planet, and therefore stand to receive what scant water may yet travel over the surface. They thus become fertilized, while higher regions escape the freshet, and remain permanently barren. That they were once seas we have something more than general inference to warrant us in believing.
There is a certain peculiarity about the surface markings of Mars, which is pretty sure to strike any thoughtful observer who examines the planet with a two or a three inch object-glass,—their singular sameness night after night. With quite disheartening regularity, each evening presents him with the same appearance he noted the evening before,—a dark band obliquely belting the disc, strangely keeping its place in spite of the nightly progression of the meridians ten degrees to the east, in consequence of our faster rotation gaining on the slower rotation of Mars. By attention, he will notice, however, that the belt creeps slowly upwards towards the pole in all other respects. Then suddenly some night he finds that it has slipped bodily down, to begin again its Sisyphus-like, inconclusive spiral climb.
Often as this rhomb-line must have been noticed, no explanation of it has
With this fact noted, let us return to the water formed by the melting of the ice-cap, at the time it is produced around the south pole. We may be sure it would not stay there long. No sooner liberated from its winter fetters than it would begin, under the pull of gravity, to run toward the equator. The reason why it would flow away from the pole is that it would find itself in unstable equilibrium where it was. Successive depositions of frost would have piled up a mound of ice which, so long as it remained solid, cohesion would keep in that unnatural position, but the moment it changed to a liquid this would flow out on all sides, seeking its level. Once started, its own withdrawal would cause the centre of gravity to shift away from the pole, and this would pull the particles of the water yet more toward the equator. Each particle would start due north; but its course would not continue in that direction, for at each mile it traveled it would find itself in a lower latitude, where, owing to the rotation of the planet, the surface would be whirling faster toward the east, inasmuch as a point on the equator has to get over much more space in twenty-four hours than one nearer the pole. In short, supposing there was no friction, the surface would be constantly slipping away from under the particle toward the east. As a result, the northerly motion of the particle would be continually changing with regard to the surface into a more and more westerly one. If the surface were not frictionless, friction would somewhat reduce the westerly component, but could never wholly destroy it without stopping this particle.
We see, therefore, that any body, whether solid, liquid, or gaseous, must, in traveling away from the pole of a sphere or spheroid, necessarily deviate to the west as it goes on, if the spheroid itself revolve, as Mars does, in the opposite direction.
This inevitable trend induced in anything flowing from the pole to the equator is precisely the one that we notice stereotyped so conspicuously in the Martian south temperate markings. Here, then, we have at once a suspiciously suggestive hint that they once held water, and that that water flowed.
Corroborating this deduction is the fact that the northern sides of all the dark areas are very perceptibly darker than the southern ones; for the northern side is the one which a descending current would plough out, since it is the northern coasts that would be constantly opposing the current's northerly inertia. Consequently, although at present the descending stream be quite inadequate to such task, it still finds its way, from preference, to these lowest levels, and makes them greener than the rest.
Though seas no longer, we perceive, then, that there is some reason to believe the so-called seas of Mars to have been seas in their day, and to be at the moment midway in evolution from the seas of the earth to the seas of the moon.
Now, if a planet were at any stage of its career able to support life, it is probable that a diminishing water supply would be the beginning of the end of that life, for the air would outlast the available water. Those of its inhabitants who had succeeded in surviving would find themselves at last face to face with the relentlessness of fate,—a scarcity of water constantly growing greater, till at last they would all die of thirst, either directly or indirectly; for either they themselves would not have water enough to drink, or the plants or animals which constituted their diet would perish for lack of it,—an alternative of small choice to them, unless they were conventionally particular as to their mode of death. Before this lamentable conclusion was reached, however, there would come a time in the course of the planet's history when water was not yet wanting, but simply scarce and requiring to be husbanded; when, for the inhabitants, the one supreme problem of existence would be the water problem,—how to get water enough to sustain life, and how best to utilize every drop of water they could get.
Mars is, apparently, in this distressing plight at the present moment, the signs being that its water supply is now exceedingly low. If, therefore, the planet possess inhabitants, there is but one course open to them in order to support life. Irrigation, and upon as vast a scale as possible, must be the all-engrossing Martian pursuit. So much is directly deducible from what we have learned recently about the physical condition of the planet, quite apart from any question as to possible inhabitants. What the physical phenomena assert is this: if there be inhabitants, then irrigation must be the chief material concern of their lives.
At this point in our inquiry, when direct deduction from the general physical phenomena observable on the planet's surface shows that were there inhabitants there a system of irrigation would be an all-essential of their existence, the telescope presents us with perhaps the most startling discovery of modern times,—the so-called canals of Mars. These strange phenomena, together with the inferences to be drawn from them, will form the subject of the next paper.
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