M A R S is the fourth planet from the Sun, whose mythological name was the Roman god of war. To the Ancient Greeks he was Ares who in legend continually lusts for strife, battle and war. He holds in his hands a large metal shield, shaped and forged conveniently from a fallen iron meteorite after its fiery descent to Earth.
Mars is commonly referred as the “Red Planet” even though the naked-eye ruddy colour is more akin to orange or orangery-red. Much smaller than the Earth, Mars is 6,794 km across compared to 12,700 km. (53%), and is only 11% by mass. Its orbit averages some 1.52 AU or 228 million kilometres (km) from the Sun, but appears highly eccentric — varying between 206.6 million kilometres at periapsis and 249.2 million km at apsis. At opposition, Mars can be as close to Earth as 54.5 million km., or as far away but as 401.3 million km at conjunction. Combining Earth’s 365.25 day year with the 686.98 days orbital period of Mars, finds that successive oppositions occur once every 780 days or so — roughly two years and two months. This causes both favourable and unfavourable oppositions, affecting its apparent size and general telescopic appearance. Mars during at opposition may brighten to −2.8 magnitude — brighter than the star Sirius or the planet Jupiter — where it can display an apparent disk as large as 25.7 arc seconds.
Favourable close perihelia or perihelic oppositions are either fifteen or seventeen years apart. During unfavourable aphesis or aphetic oppositions, the planet shrinks to the apparent maximum size of 10.1 arcsec and only brightens to −0.8 magnitude. The last most anticipated opposition occurred on 27th August 2003 when it had one of its closest approaches to Earth at the distance of 0.372 AU or 55.6 million kilometres. Another closer opposition will not again occur until 9th September 2729 AD. During the most distant conjunctions, when nearest the Sun, the size may fall below 3.5 arcsec and +4.5 magnitude.
Except near the time of opposition, and roughly two months either side of it, Mars appears quite small and disappointing even in the largest of telescopes. We usually can see many faint outlines of various hues and colours that do change significantly as the planet rotates over several hours. These match well with established planetary surface features. Some greens and blues colours are often prominent but are optical illusions formed by contrast effects between the various large Martian features. Careful observation reveals these are cyclical — confirming the rotational period is some thirty-seven minutes longer than Earth’s twenty-four hours. The Martian disk also displays snow-white polar caps. These appear quite prominent because of the significant contrast and particularly enhanced by the 25° tilt of Mars’ axis.
Similar to Earth, Mars rotates once every 24 hours 37 minutes with the planetary axis being tilted by 25° 10′ to the ecliptic. Like Earth, Mars has regular seasons, often shown by the polar caps that slowly enlarge then decrease as the Martian year progresses. Polar caps are composed of a frozen mixture of water and dry ice (CO2), whose atmospheric pressure is only one-hundredth that of Earth’s.
Atmospheric composition comprises about 95% carbon dioxide, some nitrogen, argon, and traces of oxygen and carbon monoxide. Midday equatorial temperatures may reach 15°C on the equator, but the average is more like −50°C. At nighttime this can descend as low as −110°C.
We also sometimes see when Mars’ orbit is closest to the Sun, the appearance of planet-wide dust storms with high winds exceeding 24±6 metres per second. These can ravage the surface over weeks or even months, to obscure most of the surface from view. The prominent rusty red colour of Mars consists of super-oxygenated iron oxide (Fe2 O4) that has been eroded into a very fine powder.
Mars also shows direct evidence of early geological activity, such as volcanoes, canyons and fault-lines: and such activity may still be continuing. Three very large extinct shield volcanoes form an extensive line in the equatorial Tharsis Montes region. The fourth and largest is Olympus Mons, some 1800 km. northwest, spanning about 640 kilometres to its base with its 80 km cauldron towering above the plains by some 25 km — easily dwarfing Earth’s tallest mountain, Mount Everest. Another significant geological feature is Valles Marineris — a large canyon some 6 km deep and more than 5000 km long.
Evidence also points towards the existence of water in the distant past, as the Martian surface shows ravines, river beds and flat pans. It has been determined that several billion years ago that the planet was once very much like Earth and included extensive seas or oceans. In time, this water has either escaped into space or has become buried then frozen deep under the Martian soil.
Interplanetary Visits from Earth
Many spacecraft have ventured to Mars. First was Mariner 4 in 1962 that found the surface of the Red Planet littered with craters. Since then, an armada of subsequent spacecraft, including orbiters, landers and rovers has followed this mission almost every two years. For sometime in the 1960s and 1970 there was a space race between the United States of America an the Soviet Union. Two of the latest missions have proved very successful and have yielded an enormous amount of data and images. From orbit has been the Mars Orbiter. On the surface has been the robotic rovers of Spirit and Opportunity. These two rovers have survived well past their projected life, but continue to run at the current time of writing (September 2007).
In the coming decades, even more sophisticated spacecraft will continue visiting Mars — and eventually all some dedicated manned mission in the not too distant future.
Life on Mars
Known conditions on the surface of Mars are certainly very inhospitable, with prospects of existing life being probably slim. This assumption relies on various criteria like; the extreme low temperatures, strong ultraviolet radiation from the sun, lack of protective ozone and the arid environment — but strong speculation that the planet may harbour some form of life continues.
This generally popular concept was born with the astronomer Percival Lowell in the 1890’s, who believed that he could see many ‘canals’ criss-crossing the surface of the planet. He had immediately assumed this was the direct evidence of some ancient civilisation suffering on a dying planet from thirst. For seventy-odd years his views ignited the imaginations of people throughout the world. The wildest of these fantasies perhaps reached its pinnacle with the panic delivered by the famous Orson Welles’ whose night broadcast in 30th October 1938 dramatised in the book “The War of the Worlds.” Originally written by H.G. Wells in 1898, this science fiction novel held many new concepts that were derived from the observations of Giovanni Schiaparelli (1835-1910), who described various lines across Mars as ‘canali’, which in Italian means literally open channels. Others then interpreted this to mean ‘canals’, and from this the story was stretched, where it became popularly believed that this was evidence of some alien race. This was stated as proof of an ancient and old civilisation, and fancifully assuming it to be probably dying, and were directing water from the poles to the warmer equatorial regions of the planet to grow their crops.
Yet it is only in recent times that we can begin to prove or disprove the reality of Martian life. The first scientific expedition to establish this happened during June 1976, when the two American Viking landers visited Mars. The aim was to take surface samples for analysis, and observe any changes in the material for signs of biological metabolism. No evidence for life was actually found, but this result was not finally conclusive, as the fixed landers may have been placed just in the wrong location. We may have also done the wrong test, as it is assumed that such life would be carbon-based like life on Earth. If life does really exist on Mars, it would have to be very hardy : being likely either bacteria or simple kinds of organisms. Another possibility is that microbial life once existed in the early Mars history, but has since perished. Today, Mars is likely a dead world.
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Last Update : 6th October 2019
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