The fourth known planet out from our sun, the planet Mars has long held a singular fascination for humankind. Its distinct red colour created an association with blood and battle: so much so that it was named for the local god of war across many different cultures; and even to this day astrological associations centre around conflict. Its occasional and predictable retrograde movement directly inspired models of the universe from Ptolemy’s heliocentric vision to our current understanding of our solar system. Especially in the last two centuries, we have started to wonder seriously if it could be another source of life in the universe.
Mars lies at an average distance of 227.9 million kilometres from the sun, approximately one and a half times as far away as the Earth. It has two moons, Deimos and Phobos, both irregular in shape and very small: Phobos is approximately 21 kilometres in diameter, while Deimos is only half that. Its day is almost exactly the same as Earth’s, only half an hour longer; as is its axial tilt of 25 degrees (compared to Earth’s 23.5 degrees). Thus, while the year is almost twice the length of Earth’s (687 Earth-days), Martian days and seasonality are comparable.
Although its physical size is half that of Earth’s (6,800 kilometre diameter), its gravity is only slightly more than a third of Earth’s, due to its lower density. This results in Mars having a very thin atmosphere (0.6 kilopascals), only half a percent of the Earth average air pressure (101.3 kilopascals). At its densest, it approximates that found on Mount Everest. Although the Martian atmosphere is dominated by carbon dioxide (95.3%), its density is not sufficient to create a greenhouse effect. Secondary elements of nitrogen (2.7%), argon (1.6%), oxygen (0.13%), and water (0.03%) can also be found. The average surface temperature is -63 degrees Celsius. Coupled with the distance from the sun, the incapability of such a thin atmosphere to retain heat keeps Martian icecaps at a temperature cold enough to freeze carbon dioxide and can even reach extremes of -120 degrees Celsius, although occasional equatorial temperatures of up to 20 degrees Celsius are warm enough to occasionally allow water in liquid form. In fact, some of the rock formations suggest that flowing water could have been much more common in the distant past. The combination of temperature and pressure differential is sufficient to support very intense seasonal winds.
Similarly intense geological activity have created extreme altitude variations. At the lowest is Valles Marineris, a 4,000 kilometre valley that reaches depths of up to six kilometres. At the other extreme is Olympus Mons, a volcanic mountain that rises 25 kilometres above its surrounding plain. The dominant mineral material, as determined from spectra and surface analysis, is basalt and silica, with surface iron oxide creating the characteristic rust-red colour. Some parts of the planet’s crust have been found to be band-magnetised in alternating patterns, similar to structures found on Earth’s ocean floors. Known geological processes to have influenced Mars are wind, vulcanism, meteoric cratering, liquid water, gravity (landslides), standard tectonic plating.
While much speculation has centred about the possibility of life on Mars, scientifically-based arguments about whether life on Mars exists or could at one time have existed are far from resolved. The most active area of current debate centres around whether or not structures found in Mars-originating meteorites are in fact fossil bacteria. The active Mars Rover may help us find evidence to support or reject this theory.