Mars and Its Canals

by Percival Lowell

4. A temperature colder than ours, but above the Fahrenheit freezing-point, except in winter and in the extreme polar regions;

5. Vegetation.

First and foremost of these is air. In order to make it possible for vital processes of any sort to take place, the body of a planet must be clothed with an atmosphere, by the modesty of nature, the old astronomers would have said. Such a covering subserves two purposes: it keeps out the cold of space, thus permitting the maintenance of a temperature sufficient to support life, and it affords a medium through which metabolism can go on.

Now the presence of air is attested first and foremost by the fact of change in the Martian markings, (12), (13), (26), (28), and (35). The changes observed are conspicuous; are both inorganic (in the case of the polar caps), (12), (13), and (35), and metabolic or organic, (26) and (28), (in the case of the blue-green areas); that is, they consist of building up as well as of pulling down and are planet-wide in occurrence. Such changes could not occur in the absence of an atmosphere. They show that this atmosphere consists of water vapor, (5), carbonic acid, and oxygen, (28).

The limb-light, the apparent evidence of a twilight arc and the planet’s low albedo indicate that this atmosphere is thin. The appearance of the surface, (35), suggests cold, indicative again of a thin air. Such tenuity is in accord with what a priori principles would lead us to expect, and tends to show that reliance on general principles is here not misplaced, a point of some interest.

Lastly, the occurrence of clouds, (34), visibly floating and traveling over the surface, and haze at times, (38), proves in another way the existence of the medium in which alone this could be possible.

Water is the next substance vital to planetary life. As to its actual presence the polar caps, (4)-(12), have most to say; as to its relative absence, the rest of the disk, (17)-(22). The forthright conception of the polar caps as composed of snow and ice is borne out by further investigation into what could cause the observed phenomenon. Carbonic acid, the only other substance we know capable in any way of resembling what we see, turns out not capable of producing one important detail of the caps’ appearance, the blue band, (5), which accompanies them in their retreat. Water alone could do this.

The melting of the caps shows that water vapor must be a constituent of the Martian atmosphere. Moreover, as the molecular weight of water vapor is less than that of oxygen or nitrogen or carbon dioxide, if the former can exist in the atmosphere of the planet, a fortiori must these other gases. So that from this we have knowledge of the possibility of the presence of oxygen, nitrogen, and carbon dioxide there. From (28) we saw that their actual existence is demonstrated.

The next step is the ascertainment that the water is in very small amount. The extensive melting of the caps, (7), shows their quantity to be inconsiderable, which is the first fact pointing to a dearth of water. The second comes from the aspect and behavior of the reddish-ochre regions which proclaim them deserts, (18) and (19); the third from the detection of the character of the blue-green areas as not seas, (20), (21), and (22). In several different ways, study of these regions asserts their non-aquatic constitution, the easiest to appreciate being that they are traversed by permanent dark lines and other equally sedentary markings, (22). No bodies of water, therefore, are to be seen outside of the ephemeral polar seas, immediately surrounding the caps as they melt.

This leads us to the third presence on Mars indicative of a living world: vegetation. The other two spoke of substances necessary to life, the premises in the case, this one of organic existence itself, its conclusion. The evidence consists of static testimony from the look of the blue-green areas, (23), and of kinematic derived from their behavior, (24), (25), (26), and (27). Vegetation would present exactly the appearance shown by them, and nothing that we know of but vegetation could. But suggestive as their appearance is, it is as nothing compared with the cogent telltale character of their behavior. The seasonal change that sweeps over them is metabolic, constructive as well as destructive, that is, and proclaims an organic constitution for them such as only vegetation could produce. In tint their metamorphoses are those of the same substance. For the blue-green lapses into ochre and revives again to blue-green just as vegetation does on our own Earth at the proper season of the year, taking both the Sun and the advent of water into the reckoning. Furthermore, certain of the largest dark areas turn to a chocolate-brown at times, which is the color of fallow ground and suggestive, at least, as occurring where the blue-green at other seasons is the most pronounced. Lastly, the change occurs at the epoch at which, from a knowledge of the melting of the polar caps, theory demonstrates that it ought to take place if it be due to the action of vegetation.