Favourable Opposition Of Mars In May

Press, Volume CIX, Issue 31975, 30 April 1969, Page 6

Favourable Opposition Of Mars In May

Probably there is no planet that attracts greater public interest than Mars. This is largely through speculations as to the possibility of life existing on Mars and its many similarities to the Earth. However, its orbit is much more eccentric with the result that its distance from the Sun varies widely between 129 million and 155 million miles.

Mars has a synodic period of 780 days but the intervals between successive oppositions can vary between 764 and 810 days because of the eccentricity of its orbit.

' This year the planet i reaches opposition on May 31 (when it will be only 45.1 million miles from the Earth. Nine days after opposition the two bodies make their closest approach, being some 500 thousand miles closer than at opposition. The oppositions on August 10. 1071. and October 25. 1973, are even more favourable as then the separation of the Earth and Mars will be 34.9 million and 40.5 million miles respectively. Despite the space probes due to pass close to Mars, earth-bound astronomers will devote a great deal of attention to the planet over the next few months. Tiny Moons Mars has two moons, Phobos (panic) and Deimos (terror), so named from Book XV of the “Iliad" where there is a description of Mars descending from Olympus to avenge the death of his son. Ascalaphius. Phobos revolves ground Mars in 7 hours 39 minutes at a distance of [5840 miles. Its diameter is 10 I miles. Because of the closeness to the planet Phobos has a very high velocity. As a result it rises in the west and sets in the east Tn the interval between rising and settling it passes through all its phases. Deimos, at a distance of ;14.500 miles from Mars, is a globe a mere five miles in diameter. It takes 30 hours 18 minutes to complete one revolution Since this is only slightly more than the rotational period of Mars itself. Deimos appears to move very slowly relative to the Martian surface. It is thus visible from any one point on Mars for 64 successive hours with the result that it goes through all its phases twice before setting. Both Phobos and Deimos were discovered by Asaph Hall at the very favourable [opposition of 1877. It is curious that two writers had described these tiny moons in novels written some 150 [years earlier In “Gulliver’s Travels" Swift, in writing of the astronomers of Laputa, described their discovery of two satellites revolving around Mars. Voltaire, in his novel “Micromegas.” also refers to the two Martian moons. Polar Caps At the 1969 opposition the telescopic disc of Mars will appear roughly half the she of that of Jupiter. The best viewing conditions will be from our latitudes as the > planet will be well south of 'the celestial equator. Earlier this year the north polar cap of Mars commenced to shrink and in May, which corres- ■ ponds to late summer on .Mars, it will attain its minimum size. Later in the year Ithe south polar cap will (become visible as it emerges 'from the haze above it in July. It will be seen best in September when the south [pole is tilted towards the (Earth.

It was accepted for many years that the polar caps con■sisted of frost or snow which melted as summer advanced. The objection raised to this theory was that as the frozen water evaporated the molecules would eventually escape from Mars. This meant that the amount of water vapour in the atmosphere would be very small and it was suggested that it was replenished by water released from the rocks. The most recent measurements of the temperature at mid-day at the poles gives values around -170 degrees F. This result agrees with the theory that the polar caps are frozen

carbon dioxide at a temperature of about -200 degrees F.

Fleeting Clouds

Mars has a thin atmosphere, which is, however, dense enough to permit the formation of clouds and haze. The clouds can take several forms and on occasions, such as in 1956, storms have been seen sweeping across the surface of the planet. Some of the clouds are large and yellowish and move over the surface. These are probably dust clouds. More common are the clouds with a bluish tint. These are seen at Martian sunrise and sunset and may be due to small droplets of water. Bright white clouds were thought to be similar to our own cirrus clouds and composed of ice crystals. It is now by no means certain that this is so. Arid Surface A telescopic view of Mars is apt to disappoint the layman since the planet lacks the conspicuous detail of Jupiter or the beauty of Saturn. The globe generally seems reddish or orange with one, or both, of the polar caps visible and intensely white. Several large dark areas can be seen. These are generally a greyish colour. When first seen they were thought to be oceans and were called maria. To the trained eye there is a wealth of detail and colour. The finer detail is. however, difficult to see and is only glimpsed during the moments of best seeing.

This accounts for the wide differences in the records of competent observers, especially in the cansls. These appear as straight narrow lines. They were first discovered by an Italian astronomer. Schiaparelli, in 1877 He called them canali, meaning channels, but it was translated as canals. This immediately gave rise to the speculations as to the possibility of life on Mars since canals implied that they must have been constructed by intelligent beings. Whilst many observers have recorded these straight markings, other equally competent observers have failed to see anything that could be classed as straight lines. With the 200 in Palomar telescope: the largest feature that could possibly be resolved would be over five miles across. Our atmosphere conditions push this limit up to an object around 30 miles wide. Whilst some of the more prominent canals have been photographed there is considerable doubt as to the existence of the many finer ones. Under the very best seeing conditions some observers consider these actually consist of small disconnected spots. With inferior seeing the human eye tends to connect such features into straight lines. So the very existence of many of the finer markings on Mars remains controversial. Life On Mars? The fanciful picture of the canals being waterways, constructed by intelligent beings, to convey water from the melting polar caps to the arid equatorial regions in a last struggle for existence, does not stand up under modern investigations. Whilst Mars still remains a planet of mystery it seems likely that it is incapable of supporting life as we know it. In the equatorial regions the temperature is around -■135 degrees F. near dawn and rises to +BO degrees F. shortly after noon, according to a recent investigation by

David Morrison of Harvard University. The atmosphere is thin but sufficient to permit winds of up to about 20 miles an hour. A very small amount of water vapour, close to the surface, would account for the white frost areas formed In the equatorial regions after sunset, and which persist for a brief period after sunrise. The surface is probably pitted with small craters, although the absence of shadows indicate that no high elevations exist, it is probable that the atmosphere is largely nitrogen in various forms that would be poisonous to plant life in small quantities. If the amount is large it would be poisonous to humans and animals. The space probes, now on their way to fly past Mars, will throw new light on this mysterious planet. But it seems most unlikely that this planet can support intelligent life: at least as we know it on the Earth.