MARS is the fourth planet from the Sun In mythology, Mars whose Greek equivalent is Ares, is named after the Roman god of war, who legend says continual lusts for battle and war. He is said to hold a metal shield shaped from a fallen iron meteorite that was forged during its fiery descent to Earth.

Mars is commonly referred as the “Red Planet” even though the naked-eye colour is mainly akin to a ruddy orangery-red Much smaller than the Earth, Mars is 6 794 km across and is only 11% by mass. The orbit averages some 1.52 AU or 228 million kilometres (km) from the Sun, but is highly eccentric - perapsis being 206.6 million km and apsis 249.2 million km. At opposition, Mars can be as close to Earth as 54.5 million km or at conjunction as far as 401.3 million km away. Combining Earth’s 365.25 day year with Mars’s 686.98 days means successive oppositions occur once every 780 days or two years and two months. This causes both favourable and unfavourable apparitions that affect the general telescopic appearance. Mars may brighten to -2.8 magnitude and display a disk as large as 25.7 arc seconds.

Favourable perihelic oppositions are between fifteen and seventeen years apart. During unfavourable aphetic oppositions, the planet shrinks to the maximum size of 10.1 arc seconds and only brightens to -0.8 magnitude. The most anticipated occurs this year on the 27th August 2003 when it will have one of its closest approaches to Earth at a distance of 0.372 AU or 55.6 million kilometres. Such a closer opposition will not occur again until 09th Sep 2, 729AD. During the most distant conjunctions, the size may decrease below 3.5" and may drop below +4.5 magnitude.

Similar to Earth, Mars rotates once every 24 hours 37 minutes with the planetary axis being tilted by 25o to the ecliptic. So Mars has regular seasons, shown by the polar caps that slowly enlarge then decrease as the Martian year progresses. The polar caps are a frozen mixture of water and dry ice (CO2). Atmospheric pressure is one-hundredth of Earth’s, comprising 95% carbon dioxide, nitrogen, argon, with traces of oxygen and carbon monoxide. Midday equatorial temperatures may reach -15oC on the equator, but the average is more like -50oC. At nighttime this descends as low as -110oC. We often see when Mars is closest to the Sun, the creation of dust storms moving at high wind velocities of 24±6 metre per second. These can ravage the surface for weeks or even months, and obscure the planetary surface from view. The red colour consists of a kind of super-oxygenated iron oxide (Fe2 O4) ground by erosion into a very fine powder.

Many spacecraft have ventured to Mars. The first was Mariner 4 in 1962. An armada of subsequent spacecraft, including orbiters, landers and rovers has followed this, and found the Red Planet’s surface littered with craters. It also shows signs of geological activity, such as many volcanoes, canyons and fault-line surface cracks. Five large volcanoes appear in a line, the biggest being the 300 km wide Olympus Mons. The cauldron is 64 km at its widest, whose summit towers above the plain by 24 km. Valles Marineris is a large canyon 6 km deep and more than 5 000 km long. Evidence points towards the existence of water in the distant past, as Mars shows ravines, river beds and pans across the planet’s surface. It is possible that perhaps the planet was once like Earth several billion years ago that included oceans. In time, this water has either escaped into space or has become buried and frozen under the Martian surface. Presently there is evidence for both these possibilities. In the coming decades, even more sophisticated ships will visit Mars - and eventually even a manned mission in the no too distant future.

Conditions are certainly inhospitable, and the prospects of existing life are unlikely. This is based on criteria like; reflected by the low temperatures, strong ultraviolet radiation, lack of ozone and the arid environment; speculation that the planet may harbour life continues. This generally popular idea was born with the astronomer Percival Lowell in the 1890’s. He believed that he could see many ‘canals’ criss-crossing the surface of the planet and immediately assumed this was the direct evidence of some ancient civilization on a dying planet. For seventy-odd years he ignited the imaginations of people. Finally to prove or disprove the reality of Martian life, two American Viking landers visited Mars in June 1976 - but no evidence for life was found. If life does exist there, it would have to be very hardy and would be likely either bacteria or simple organisms. Another possibility is that microbial life once existed in the early history, but today it is likely a dead world.

Except near opposition, Mars appears quite disappointing even in the largest of telescopes. We can see faint features of various colours changing as the planet rotates over several hours. These match well to known features on the planet’s surface. Some green and blue colours are optical illusions formed by contrast effects. The disk also displays snow-white polar caps that appear quite prominent because of the significant contrast.

Orbiting close to Mars is the two moons, Phobos and Deimos. Both are irregularly shaped being only tens of kilometres in size. Phobos orbits in only 0.319 days while Deimos orbits in 1.262 days. A moderately large telescope is needed to see them.


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Last Update : 23rd May 2005

Southern Astronomical Delights © (2005)


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