Mars

Mars

The planet Mars is named after the Roman god of war because of its red colour. It orbits the sun once in nearly two years at an average distance of about 142 million miles. It is brightest and most easily observed when it is in opposition, or in a direction opposite to that of the sun, but even then it can come no closer than about 35 million miles. The large distance, coupled with the planet’s comparatively small diameter of 4,200 miles, makes all but the coarser surface markings difficult to detect with earth-based telescopes.

During the Mars night and especially in the polar regions, the ground temperature falls well below the freezing point of water.

Mars. Photo by NASA in public domain

The red color of Mars is thought to be due to the existence of large deserts of orange-red dust. Any oxygen the planet once had in its atmosphere is now probably imprisoned in the surface rocks in the form of iron oxides. Carbon dioxide and water vapour have been detected in the Martian atmosphere, but the amount of water vapour is so small that it is were all turned into water and would cover the planet to a depth of only three-thousandths of an inch. White, high-altitude clouds, presumably composed of ice crystals, occasionally drift over the surface or appear beyond the planet’s edge or limb. A yellow haze, thought to be swirling dust clouds, sometimes obscures large areas for days or even weeks.

Mars has two white polar caps and various permanent dark areas. The caps change considerably in size with the Martian seasons, being largest in winter and smallest in summer. The dark areas also change with the seasons: a few change hardly at all, but the rest tend to darken as the polar cap in their particular hemisphere gets smaller. The effect is as if a wave of darkening were moving from the polar cap toward the equator.

A Parched World

The gravitational pull of Mars is much less than that of the Earth: an astronaut who weighed 140 pounds of the Earth would weigh only 56 pound on Mars. Consequently the Martian atmosphere is thin – so thin, perhaps, as to rule out all known forms of life. We have good reasons for thinking that the general climate on Mars would be similar to that on a dry, cold desert some 11 miles above the Earth’s surface.

The combined length of day and night on Mars is slightly longer than on the Earth. But during the day, at the planet’s equator, the temperature reaches a high of only 30 degrees centigrade.

Canals on Mars?

These changes encouraged the idea that Mars possessed some form of vegetation partly nourished by flows of moist air from the shrinking polar caps. One astronomer, Percival Lowell, suggested that the moisture took the form of water which moved towards the equator through artificial waterways. He made an intensive study of Mars during its close approach or opposition of 1894-1895, and concluded that the certain dusky streaks, first seen in 1877 by the Italian astronomer Giovanni Schiaparelli, were canals designed and built by intelligent Martians.

Although he drew them as forming a highly geometrical network of straight lines, he did not claim to see the canals themselves, but merely the vegetation growing on their banks.

Lowell’s conclusions have no foundation in the light of modern observations, but the precise nature of the dark areas still remains a mystery. One modern view, based largely on radar studies, is that they are high plateaux, comparatively free from dust. Another is that they are areas where alternate freezing and thawing on the ground has produced a highly porous surface. The polar caps certainly cannot produce large quantities of free water, for the atmospheric pressure on Mars is so low that ice and snow would not melt but sublime, or pass directly from the solid to the vapour state. The caps are undoubtedly quit thin, but whether they are deposits of snow, hoar frost, solid carbon dioxide, or a combination of all three, is still an open question.

Mariner IV. Photo by NASA in public domain

Mariner IV

If canals bordered by fringes of vegetation exist on Mars they should have shown up on the close-up photographs taken in July, 1965, by Mariner IV. As this little planetary probe passed within 9,000 miles of Mars its camera photographed sections of a long, narrow strip of the planet’s surface. Much to everyone’s surprise, the photographs showed dozens of ring mountains similar in appearance to some of the craters on the moon. Nearly 12 per cent of the well-defined rings have central peaks, but several others are ill-defined, as if almost eroded away by dust-laden winds. Studies of the photographs have led some experts to interpret certain linear features as mountain ridges similar to those found on the beds of oceans on the Earth. But any oceans Mars might have possessed dried up long ago.

Mars has two tiny satellites, discovered by the American astronomer Asaph Hall in 1877 and named Phobos and Deimos. Strangely enough, the existence of these flyweight moons was mentioned by Jonathan Swift in his Gulliver’s Travels some 150 years before Hall’s discovery. Phobos, 10 miles in diameter, flies around Mars in seven hours, 39 minutes at a distance of 5,800 miles from the planet’s center. It therefore revolves roughly three times faster than Mars rotates and consequently travels across the Martian sky in a west-to-east direction. Deimos, five miles across, has a period of revolution of 30 hours, 18 minutes and is 14,600 miles from the planet’s center. Since the period is only slighter longer than the Martian day. Deimos moves slowly across the Martian sky in an east-to-west direction.