RIDDLE OF MARS

Evening Post, Volume CVII, Issue 144, 19 June 1924, Page 9

RIDDLE OF MARS

VERY MUCH ALIVE WORLD MYSTERY OF THE CANALS SCIENTISTS PREPARING'FOR THE PLANETS APPROACH. . 11-' Continuing his article, published in a recent issue.of the "New York Times" on the possibility of communicating with Mars during that planet's nearer approach to the earth, in the course of the j next few. weeks, M. Flammarion, the I French astronomer and authority on Martian geography, goes on to say that it will be'on 3rd July that the earth is at its aphelion. The most favourable positions of Mars, therefore, are those it assumes when, as happens tin's year, the opposition occurs when Mars is at its perihelion.. At such a time the telescopic diameter of Mars, increases to 25 seconds of arc, while when the planet is at its greatest distance from the earth its diameter is. less than four seconds. Just what does. this angular magnitude mean? Imagine a disk 25 centimetres in diameter; at a. ' distance of 80 metres, for example, a football seen at that distance. It is visible to tbo naked eye; but you could.not distinguish an ant crawling across the surface of that globe. Fortunately the discoveries of optic science come to our rescue. An enlargement of 400 times—that generally^ used in Martian observations—brings the'sphere to within 20 centimetres of us. Picture a tiny earth, of the size of the football, seen at that, distance; miniature continents can be distinguished, the Alpine giants are traced as shadows whose relief we cannot guess. The oceans, are indicated by bluish spots, more or-less extensive, more or less deep I in shade. No traces of human activity are visible. Only, geographic, configurations are distinct. A long time ago I constructed an "aerographic" globe,' that is, a Martian globe, which, held in one's hand, shows the geographic details of the planet. ■

On the map of Mars, at 63' degrees longitude and the Equator, can be seen a little round lake .that has been.named Fons Juventae, or Fountain of Youth. I have always been particularly interested in it. The little lake is 120 to 150 kilometres wide, and is connected by a channel 400 kilometres long and 60 wide with the neighbouring sea, the Gulf of Aurora. The atmosphere in this region is usually very clear, and conditions of visibility are much better there than' in other frequently observed districts, such as Hesperia and Little Syrta. During the opposition, of 1918 the Fountain of Youth and jts little channel were almost constantly visible. On this . neighbouring world, therefore, we can study features that are 120, 100, and 6J. kilometres wide. It is easier to see' a fine thread than an isolated object of the same width. A channel .60 kilometres wide is incomparably easier to distinguish than a circle of; that diameter. back as' 1636 Fontana began the methodic observation of Mars. We have drawings made by Huyghens in 1659; by Maraldi, William Herschel, and Schroeter in the eighteenth century; by Maedler,,'Secchi, Lockyer, Green, Dawes, Terby, and Schiaparelli in the nineteenth, and by Lowell, W. H. Pickering JarryDesloges (to .mention' only the principal observers) in the twentieth' century. It can be said that the totality of Martian geography, from the Equator to the poles, was known before the whole of terrestrial, geography. In spite of our polar expeditions of recent years, astronomers are more familiar with the poles of Mars than are the geographers with the poles of the earth. In- the telescope we can see Mars turning before our eyes, from west to east, like the earth. The planet's geographic configuration being well known, we can predict which regions will come within the range of the telescope and which will disappear. There as here some countries are 'having morning, ' ottiers noon, still others evening;'.we witness risings and settings of the sun, • and watch the hours succeeding one another, just as if we were on the moon, watching the earth turning before our eyes. . LITTLE WATER ON MARS. Wo must admit, however that the Martian landscapes are quite different from ours. The surface there, unlike that of the earth. is; not three-fourths aqueous. There are no oceans, only mediterranean seas,. and these not very deep, for we can often see their bottom. As a result.of the revolutions of the earth and. of Mars: around .the sun, the earth taking 365 days and Mars'6B7, the latter comes every 'two years in opposition to the sun, in the prolongation of a- straight. line drawn from the central star to the earth. ..And. by. combination of.the ellipses of the two orbits, the greatest proximity between ' the planets recurs every fifteen years. Thus the year 1862 was fertile in observations, and the year .1877 even more. The opposition of 1877 was marked-by. the discoveries of Schiaparelli at the Milan Observatory: w e owe to it,.indeed, the first complete aerographic map 'of this neighbouring . world, and the scientific study (continued during subsequent oppositions) of the mysterious canals. Since the Martian year is almost twice as long as ours, in the proportion of 687 days to 363, the seasons there are also of correspondingly greater length. And as the Martian orbit-is more eccentric than ours, tho difference between the duration of summer and of winter is more pronounced there. Everyone knows that the seasons of the earth, like those of the other planets, are produced by the-inclination of its axis of rotation' on the plane of its annual revolution about the sun.. A globe turning like Jupiter, almost straight and with hardly any inclination, enjoys' perpetual spring. The inclination of the earth is 23 degrees. 27 minutes, while that of Mars- is a little 'higher, 24 degrees ' H minutes, according to the most recent measurements-of Pickering. The Martian seasons arc analogous to ours in intensity, but longer. While there are" here only 93 days between 21st March and 2-2 nd June, there are on Mars 199 days between the spring equinox and the summer solstice. While on earth the festival season, that is, from 21st March to 23rd September, as of 18G days duration, there are on Mars 381 days between the spring and autumn equinoxes Ihe meteorological effects of these seasons are very marked on the' Martian globe. In .winter there is a spreading formation of snow-that melts again in spring. During severe winters, the snow spreads comparatively even further-than on our planet, as far as latitudes corresponding to our London, Cokyrio Dresden, etc. But this covering of snow is not of great thickness, and under the summer sun melts easily, sometimes even to the point of completo disappearance. * For forty years I have been drawing or photographing these snows at my Juyisy observatory, and have kept a record of them. There, as hern, succeeding years do not resemble one another.. There arc .• .warm-year's and cold . years, limes of drought and of floods. Sometimes-the polar, snows melt, so rapidly.that we can sic them disap9ttdng. Th» ic# »t the terrestrial poleo

is incomparably heavier and. more solid. The Martian temperature, for that matter, is rather higher than lower in comparison with that of the earth. The surface heat of planets, which is of such great importance with regard to the appearance of life, has its origin in the solar radiation, and seems, on the earth and on Mars, to be independent of the internal heat of the globe. (This, however, is not true for Jupiter.) But it is a mistake to consider only the distance from the sun in the calculation of these temperatures. ■■■ One is often astounded to see eminent astronomers coming to • entirely false conclusion because they forget the exceedingby important effect of the constitution of the atmospheric envelope of the planets. A WORLD OF SEASONAL CHANGES. Our atmosphere acts as a protective covering, for conserving the heat obtained from the sun and for preserving its dissipation into space. But it'is not the air itself that has this property; it is the water vapour. . A molecule of water vapour preserves solar heat 16,000 times more efficiently than does a molecule of dry air. Water is not the only substance ' endowed with this property. Others of this class are the vapours of tli« sulphuric, formic, and acetic ethers, of amylene,; of ethyl iodide, of choloform, and of carbon bisulphide. The atmosphere of Mars, though very rare, may nevertheless hold in suspension some vapours of this kind and thus preserve for the planet a surface temperature equal to or higher than the average temperature of the earth. But is is hardly necessary to imagine anything but water analogous to- our >yater; for the Martian snows are much like ours in their spreading during winter, their fusion during summer and the floods that follow their melting. The difference lies in the means of circulation. The evaporation of the Martian seas does, not give rise to clouds, rain, spring!!, and rivers. We do not see there any ramifications analogous to our system of springs, brooks, rivers, and large streams whose mouths empty into I oceans. The distribution of water" there is carried on differently, by means of mists, fogs, nocturnal hoar frosts, and light snows. Clouds do occur, but not frequently. On tihe earth, however, there are always clouds somewhere; there probably is riot a single day of the year when the entire surface of our planet is entirely unclouded so that it can be seen distinctly from space. . So we have here two absolutely different meteorological regimes. When we an unable to see Mars clearly enough to make a drawing, the obstacle usually comes from ■ our own atmosphere and not from that of the other planet. The Martian snows, it may be. mentioned, aie yellow, not white, perhaps because they are light and space, and permit the planet's body to be seen through them. Positive and direct observation reveals, besides the climatological variaations, lasting changes in the appearance, the shades, and the colour of different regions of the surface. It can properly'be said that the appearance of the earth, ■ observed 'from an aerostat or from the moon, would also show enduring variations produced by clouds, snow, periods of drought or floods, by cultivation, by seasonal changes,. etc. On Mars there are some corresponding changes and some that are different. When) convinced of these changes, I made a statement regarding them, in 1877, their existence was doubted by the majority of astronomers. They attri-. buted my observations to error and optical illusion. But since that time the fact .has been unanimously admitted. 'MARTIAN ; CANALS. A good many problems arise from these variations, independent of tho seasonal changes. It is evident, however, that this celestial neighbour of ours is by. no. means in the dead or frozen state of which it has been accused; it is a very much alive world. . . • And we have not yet mentioned the canals, their enigmatic aspect and their variations;—a network whose first interpretation was that' it had been constructed by. engineers. This mystery, too is as yet unexplained. Not all eyes see the more narrow canals, and some even go so far as to deny their existence —a singular exaggeration ! My learned friend Lowell (who used to come to Paris every other year, when Mars could not be observed), discussed with me a whole theory of. their application to the distribution over Mars of water) which is rare there- and essential for agriculture. Even before that, the eminent astronomer Schiaparelli, to whom science owes the discovery of the cometary origin of shooting stars, and who, in 1882, constructed the first really complete map of Mars, had written me in connection with this odd network: "Semel in anno licet-in-samre" (twice a year we may speak out mad fancies). At that time he presented to me an ingenious and picturesque hypothesis, supported ■ by: • diagrams, concerning the construction of the canals by Martian agriculturists for the irrigation of the land. I believe, however, that these canals might bo primitive geologic' formations, say, valleys,, that were elaborated by the inhabitants; for the network as we see it to-day seems hardly natural.' . ' July and August may tell us more about Mars than we have ever known. That astronomers, both scientific and popular, are eagerly awaiting the close passing of our celestial neighbour goes without saying.. '■'.'.