MARS

The Red Planet is our nearest neighbour on the further, as Venus is on the hither side. He is also in some ways the planet best situated for our observation; for while the greatest apparent diameter of his disc is considerably less than that of Venus, he does not hide close to the sun's rays like the inferior planets, but may be seen all night when in opposition.* Not all oppositions, however, are equally favourable. Under the best circumstances he may come as near to us as 35,000,000 miles; when less favourably situated, he may come no nearer than 61,000,000. This very considerable variation in his distance arises from the eccentricity of the planet's orbit, which amounts to nearly one-tenth, and, so far as we are concerned, it means that his disc is three times larger when he comes to opposition at his least distance from the sun than it is when the conditions are reversed. Under the most favourable circumstances—i.e., when opposition and perihelion† occur together, he presents, it has been calculated, a disc of the same diameter as a half sovereign held up 2,000 yards from the spectator. Periods of opposition recur at intervals of about 780 days, and at the more favourable ones the planet's brilliancy is very striking. The 1877 opposition was very notable in this respect, and in others connected with the study of Mars, and that which preceded the Crimean War was also marked by great brilliancy. Readers of Tennyson will remember how Maud

Ancient records tell us of his brightness having been so great on some occasions as to create a panic. Panics were evidently more easily created by celestial phenomena then than they are now; but possibly such statements have to be taken with a small grain of salt.

The diameter of Mars is 4,200 miles. In volume he is equal to one-seventh of the world; but his density is somewhat smaller, so that nine globes such as Mars would be required to balance the earth. He turns upon his axis in twenty-four hours thirty-seven minutes, and as the inclination of the axis is not much different from that of our own world he will experience seasonal effects somewhat similar to the changes of our own seasons. The Martian seasons, however, will be considerably longer than ours, as the year of Mars occupies 687 days, and they will be further modified by the large variation which his distance from the sun undergoes in the course of his year—the difference between his greatest and least distances being no less than 26,500,000 miles.

The telescopic view of Mars at once reveals features of considerable interest. We are no longer presented with anything like the beautiful phases of Venus, though Mars does show a slight phase when his position makes a right angle with the sun and the earth. This phase, however, never amounts to more than a dull gibbosity, like that of the moon two or three days before or after full—the most uninteresting of phases. But the other details which are visible much more than atone for any deficiency in this respect. The brilliant ruddy star expands under telescopic power into a broad disc whose ground tint is a warm ochre. This tint is diversified in two ways. At the poles there are brilliant patches of white, larger or smaller according to the Martian season; while the whole surface of the remaining orange-tinted portion is broken up by patches and lines of a dark greenish-grey tone. The analogy with Arctic and Antarctic ice and snow-fields, and with terrestrial continents and seas, is at once and almost irresistibly suggested, although, as will be seen, there are strong reasons for not pressing it too far.

The dark markings, though by no means so sharply defined as the outlines of lunar objects, are yet evidently permanent features; at least this may be confidently affirmed of the more prominent among them. Some of these can be readily recognised on drawings dating from 200 years back, and have served to determine with very satisfactory accuracy the planet's rotation period. In accordance with the almost irresistible evidence which the telescope was held to present, these features were assumed to be seas, straits and bays, while the general ochre-tinted portion of the planet's surface was considered to be dry land. On this supposition the land area of Mars amounts to ⁵/7 of the planet's surface, water being confined to the remaining ²/7. But it is by no means to be taken as an accepted fact that the dark and light areas do represent water and land. One fact most embarrassing to those who hold this traditional view is that in the great wealth of detail which observation with the huge telescopes of to-day has accumulated the bulk belongs to the dark areas. Gradations of shade are seen constantly in them; delicate details are far more commonly to be observed upon them than upon the bright portions of the surface, and several of the 'canals' have been traced clear through the so-called seas. Speaking of his observations of Mars in 1894 with the 36-inch refractor of the Lick observatory, Professor Barnard says: 'Though much detail was shown on the bright "continental" regions, the greater amount was visible on the so-called "seas."... During these observations the impression seemed to force itself upon me that I was actually looking down from a great altitude upon just such a surface as that in which our observatory was placed. At these times there was no suggestion that the view was one of far-away seas and oceans, but exactly the reverse.' Such observations are somewhat disconcerting to the old belief, which, nevertheless, continues to maintain itself, though in somewhat modified form.

It is indeed difficult, if not impossible, to explain the observed facts with regard, for instance, to the white polar caps, on any other supposition than that of the existence of at least a considerable amount of water upon the planet. These caps are observed to be large after the Martian winter has passed over each particular hemisphere. As the season progresses, the polar cap diminishes, and has even been seen to melt away altogether. In one of the fine drawings by the Rev. T. E. R. Phillips, which illustrate this chapter (Plate XX.), the north polar snow will be seen accompanied by a dark circular line, concerning which the author of the sketch says: 'The melting cap is always girdled by a narrow and intensely dark line. This is not seen when the cap is forming.' It is hard to believe that this is anything else than the result of the melting of polar snows, and where there is melting snow there must be water. Such results as those obtained by Professor Pickering by photography point in the same direction. In one of his photographs the polar cap was shown much shrunken; in another, taken a few days later, it had very considerably increased in dimensions—as one would naturally conclude, from a fall of snow in the interval. The quantity of water may not be anything like so great as was at one time imagined; still, to give any evidence of its presence at all at a distance of 40,000,000 miles it must be very considerable, and must play an important part in the economy of the planet.

In 1877 Schiaparelli of Milan announced that he had discovered that the surface of Mars was covered with a network of lines running with perfect straightness often for hundreds of miles across the surface, and invariably connecting two of the dark areas. To these markings he gave the name of 'canali,' a word which has been responsible for a good deal of misunderstanding. Translated into our language by 'canals,' it suggested the work of intelligent beings, and imagination was allowed to run riot over the idea of a globe peopled by Martians of superhuman intelligence and vast engineering skill. The title 'canals' is still retained; but it should be noted that the term is not meant to imply artificial construction any more than the term 'rill' on the moon implies the presence of water.

At the next opposition of Mars, Schiaparelli not only rediscovered his canals, but made the astonishing announcement that many of them were double, a second streak running exactly parallel to the first at some distance from it. His observations were received with a considerable amount of doubt and hesitation. Skilled observers declared that they could see nothing in the heavens the least corresponding to the network of hard lines which the Italian observer drew across the globe of Mars; and therein to some extent they were right, for the canals are not seen with that hardness of definition with which they are sometimes represented. But, at the same time, each successive opposition has added fresh proof of the fact that Schiaparelli was essentially right in his statement of what was seen. The question of the doubling of the canals is still under dispute, and it seems probable that it is not a real objective fact existing upon the planet, but is merely an optical effect due to contrast. There can be no question, however, about the positive reality of a great number of the canals themselves; their existence is too well attested by observers of the highest skill and experience. 'There is really no doubt whatever,' says Mr. Denning, 'about the streaked or striated configuration of the Northern hemisphere of Mars. The canals do not appear as narrow straight deep lines in my telescope, but as soft streams of dusky material with frequent condensations.' The drawings by Mr. Phillips well represent the surface of the planet as seen with an instrument of considerable power; and the reader will notice that his representation of the canals agrees remarkably well with Denning's description. The 'soft streams with frequent condensations' are particularly well shown on the drawing of April 22, 1903, which represents the region of 200° longitude (see Chart, Plate XXI.) on the centre of the disc. 'The main results of Professor Schiaparelli's work,' remarks Mr. Phillips, 'are imperishable and beyond question. During recent years some observers have given to the so-called "canals" a hardness and an artificiality which they do not possess, with the result that discredit has been brought upon the whole canal system.... But of the substantial accuracy and truthfulness (as a basis on which to work) of the planet's configuration as charted by the great Italian in 1877 and subsequent years, there is in my mind no doubt.' The question of the reality of the canal system may almost be said to have received a definite answer from the remarkable photographs of Mars secured in May, 1905, by Mr. Lampland at the Flagstaff Observatory, which prove that, whatever may be the nature of the canals, the principal ones at all events are actual features of the planet's surface.

Much attention has been directed within the last few years to the observations of Lowell, made with a fine 24-inch refractor at the same observatory, which is situated at an elevation of over 7,000 feet. His conclusion as to the reality of the canals is most positive; but in addition to his confirmation of their existence, he has put forward other views with regard to Mars which as yet have found comparatively few supporters. He has pointed out that in almost all instances the canals radiate from certain round spots which dot the surface of the planet. These spots, which have been seen to a certain extent by other observers, he calls 'oases,' using the term in its ordinary terrestrial significance. His conclusions are, briefly, as follows: That Mars has an atmosphere; that the dark regions are not seas, but marshy tracts of vegetation; that the polar caps are snow and ice, and the reddish portions of the surface desert land. The canals he holds to be waterways, lined on either bank by vegetation, so that we see, not the actual canal, but the green strip of fertilized land through which it passes, while the round dark spots or 'oases' he believes to be the actual population centres of the planet, where the inhabitants cluster to profit by the fertility created by the canals. In support of this view he adduces the observed fact that the canals and oases begin to darken as the polar caps melt, and reasons that this implies that the water set free by the melting of the polar snows is conveyed by artificial means to make the wilderness rejoice.

Lowell's theories may seem, very likely are, somewhat fanciful. It must be remembered, however, that the ground facts of his argument are at least unquestionable, whatever may be thought of his inferences. The melting of the polar caps is matter of direct observation; nor can it be questioned that it is followed by the darkening of the canal system. It is probably wiser not to dogmatize upon the reasons and purposes of these phenomena, for the very sufficient reason that we have no means of arriving at any certitude. Terrestrial analogies cannot safely be used in connection with a globe whose conditions are so different from those of our own earth. The matter is well summed up by Miss Agnes Clerke: 'Evidently the relations of solid and liquid in that remote orb are abnormal; they cannot be completely explained by terrestrial analogies. Yet a series of well-authenticated phenomena are intelligible only on the supposition that Mars is, in some real sense a terraqueous globe. Where snows melt there must be water; and the origin of the Rhone from a great glacier is scarcely more evident to our senses than the dissolution of the Martian ice-caps into pools and streams.'

Closely linked with the question of the existence of water on the planet, and indeed a fundamental point in the settlement of it, is the further question of whether there is any aqueous vapour in the Martian atmosphere. The evidence is somewhat conflicting. It is quite apparent that in the atmosphere of Mars there is nothing like the volume of water vapour which is present in that of the earth, for if there were, his features would be much more frequently obscured by cloud than is found to be the case. Still there are many observations on record which seem quite unaccountable unless the occasional presence of clouds is allowed. Thus on May 21, 1903, Mr. Denning records that the Syrtis Major (see Chart, Plate XXI.) being then very dark and sharply outlined, a very bright region crossed its southern extremity. By May 23, the Syrtis Major, 'usually the most conspicuous object in Mars, had become extremely feeble, as if covered with highly reflective vapours.' On May 24, Mr. Phillips observed the region of Zephyria and Aeolis to be also whitened, while the Syrtis Major was very faint; and on the 25th, Mr. Denning observed the striking whiteness of the same region observed by Mr. Phillips the day before. Illusion, so often invoked to explain away inconvenient observations, seems here impossible, in view of the prominence of the markings obscured, and the experience of the observers; and the evidence seems strongly in favour of real obscuration by cloud. It might have been expected that the evidence of the spectroscope would in such a case be decisive, but Campbell's negative conclusion is balanced by the affirmative result reached by Huggins and Vogel. It is safe to say, however, that whatever be the constitution of the Martian atmosphere, it is considerably less dense than our own air mantle.

During the last few years the public mind has been unusually exercised over Mars, largely by reason of a misapprehension of the terms employed in the discussion about his physical features. The talk of 'canals' has suggested human, or at all events intelligent, agency, and the expectation arose that it might not be quite impossible to establish communication between our world and its nearest neighbour on the further side. The idea is, of course, only an old one furbished up again, for early in last century it was suggested that a huge triangle or ellipse should be erected on the Siberian steppes to show the Lunarians or the Martians that we were intelligent creatures who knew geometry. In these circumstances curiosity was whetted by the announcement, first made in 1890, and since frequently repeated, of the appearance of bright projections on the terminator of Mars. These were construed, by people with vivid imaginations, as signals from the Martians to us; while a popular novelist suggested a more sinister interpretation, and harrowed our feelings with weird descriptions of the invasion of our world by Martian beings of uncouth appearance and superhuman intelligence, who were shot to our globe by an immense gun whose flashes occasioned the bright projections seen. The projections were, however, prosaically referred by Campbell to snow-covered mountains, while Lowell believed that one very large one observed at Flagstaff in May, 1903, was due to sunlight striking on a great cloud, not of water-vapour, but of dust.

As a matter of fact, Mars is somewhat disappointing to those who approach the study of his surface with the hope of finding traces of anything which might favour the idea of human habitation. He presents an apparently enticing general resemblance to the earth, with his polar caps and his bright and dark markings; and his curious network of canals may suggest intelligent agency. But the resemblances are not nearly so striking when examined in detail. The polar caps are the only features that seem to hold their own beside their terrestrial analogues, and even their resemblance is not unquestioned; the dark areas, so long thought to be seas, are now proved to be certainly not seas, whatever else they may be; and the canal system presents nothing but the name of similarity to anything that we know upon earth. It is quite probable that were Mars to come as near to us as our own moon, the fancied resemblances would disappear almost entirely, and we should find that the red planet is only another instance of the infinite variety which seems to prevail among celestial bodies. That being so, it need scarcely be remarked that any talk about Martian inhabitants is, to say the least of it, premature. There may be such creatures, and they may be anything you like to imagine. There is no restraint upon the fancy, for no one knows anything about them, and no one is in the least likely to know anything.

The moons of Mars are among the most curious finds of modern astronomy. When the ingenious Dr. Jonathan Swift, in editing the travels of Mr. Lemuel Gulliver, of Wapping, wrote that the astronomers of Laputa had discovered 'two lesser stars, or satellites, which revolve about Mars,' the suggestion was, no doubt, put in merely because some detail of their skill had to be given, and as well one unlikely thing as another. Probably no one would have been more surprised than the Dean of St. Patrick's, had he lived long enough, or cared sixpence about the matter, to hear that his bow drawn at a venture had hit the mark, and that Professor Asaph Hall had detected two satellites of Mars. The discovery was one of the first-fruits of the 26-inch Washington refractor, and was made in 1877, the year from which the new interest in Mars may be said to date. The two moons have been called Deimos and Phobos, or Fear and Panic, and are, in all probability, among the very tiniest bodies of our system, as their diameter can scarcely be greater than ten miles. Deimos revolves in an orbit which takes him thirty hours eighteen minutes to complete, at a distance of 14,600 miles from the centre of Mars. Phobos is much nearer the planet, his distance from its centre being 5,800, while from its surface he is distant only 3,700 miles. In consequence of this nearness, he can never be seen by an observer on Mars from any latitude higher than 69°, the bulge of the globe permanently shutting him out from view. His period of revolution is only seven hours thirty-nine minutes, so that to the Martian inhabitants, if there are any, the nearer of the planet's moons must appear to rise in the west and set in the east. By the combination of its own revolution and the opposite rotation of Mars it will take about eleven hours to cross the heavens; and during that period it will go through all its phases and half through a second display.

These little moons are certainly among the most curious and interesting bodies of the solar system; but, unfortunately, the sight of them is denied to most observers. That they were not seen by Sir William Herschel with his great 4-foot reflector probably only points to the superior defining power of the 26-inch Washington refractor as compared with Herschel's celebrated but cumbrous instrument. Still, they were missed by many telescopes quite competent to show them, and of as good defining quality as the Washington instrument—a fact which goes to add proof, if proof were needed, that the power which makes discoveries is the product of telescope × observer, and that of the two factors concerned the latter is the more important. It is said that the moons have been seen by Dr. Wentworth Erck with a 7?-inch refractor. The ordinary observer is not likely to catch even a glimpse of them with anything much smaller than a 12-inch instrument, and even then must use precautions to exclude the glare of the planet, and may count himself lucky if he succeed in the observation.

A word or two may be said as to what a beginner may expect to see with a small instrument. It has been stated that nothing under 6 inches can make much of Mars; but this is a somewhat exaggerated statement of the case. It is quite certain that the bulk of the more prominent markings can be seen with telescopes of much smaller aperture. Some detail has been seen with only 1¾-inch, while Grover has, with a 2-inch, executed drawings which show how much can be done with but little telescopic power. The fact is, that observers who are only in the habit of using large telescopes are apt to be unduly sceptical of the powers of small ones, which are often wonderfully efficient. The fine detail of the canal system is, of course, altogether beyond small instruments; and, generally speaking, it will take at least a 4-inch to show even the more strongly marked of these strange features. At the 1894 opposition, the writer, using a 3?-inch Dollond of good quality, was able to detect several of the more prominent canals, but only on occasions of the best definition. The accompanying rough sketch (Fig. 24) gives an idea of what may be expected to be seen, under favourable conditions, with an instrument of between 2 and 3 inches. It represents Mars as seen with a glass of 2?-inch aperture and fair quality. The main marking in the centre of the disc is that formerly known as the Kaiser or Hour-glass Sea. Its name in Schiaparelli's nomenclature, now universally used, is the Syrtis Major. The same marking will also be seen in Mr. Phillips's drawing of 1899, January 30, in which it is separated by a curious bright bridge from the Nilosyrtis to the North. The observer need scarcely expect to see much more than is depicted in Fig. 24, with an instrument of the class mentioned, but Plate XX. will give a very good idea of the appearance of the planet when viewed with a telescope of considerable power. The polar caps will be within reach, and sometimes present the effect of projecting above the general level of the planet's surface, owing, no doubt, to irradiation.

To the intending observer one important caution may be suggested. In observing and sketching the surface of Mars, do so independently. The chart which accompanies this chapter is given for the purpose of identifying markings which have been already seen, not for that of enabling the observer to see details which are beyond the power of his glass. No planet has been the cause of more illusion than Mars, and drawings of him are extant which resemble nothing so much as the photograph of an umbrella which has been turned inside out by a gust of wind. In such cases it may reasonably be concluded that there is something wrong, and that, unconsciously, 'the vision and the faculty divine' have been exercised at the expense of the more prosaic, but in this case more useful, quality of accuracy. By prolonged study of a modern chart of Mars, and a little gentle stretching of the imagination, the most unskilled observer with the smallest instrument will detect a multitude of canals upon the planet, to which there is but one objection, that they do not exist. There is enough genuine interest about Mars, even when viewed with a small glass, without the importation of anything spurious. In observation it will be noticed that as the rotation period of Mars nearly coincides with that of the earth, the change in the aspect presented from night to night will be comparatively small, the same object coming to the meridian thirty-seven minutes later each successive evening. Generally speaking, Mars is an easier object to define than either Venus or Jupiter, though perhaps scarcely bearing high powers so well as Saturn. There is no planet more certain to repay study and to maintain interest. He and Jupiter may be said to be at present the 'live' planets of the solar system in an astronomical sense.

* The opposition of a planet occurs 'whenever the sun, the earth, and the planet, as represented in their projected orbits, are in a straight line, with the earth in the middle.'

† That point in the orbit of a planet or comet which is nearest to the sun.