The fourth planet from the Sun, Mars resembles Earth in many ways. Although it is only half the size of our globe and its ferrous core is smaller, it does have seasons which last about six months because the planet takes longer to complete an orbit around the Sun. Moreover, Mars features ice caps at the poles and possesses a thin atmosphere.
Observations of Mars may be traced back to the advanced civilizations of antiquity. It was probably because of its reddish blood-like color that the planet was given the name of the god of war, Ares or Mars. Early in the 17th century Johannes Kepler formulated his three laws, which describe the movements of the planets, on the basis of Mars position measurements made by the Danish astronomer Tycho Brahe which, although few in number, were highly precise for their time. Whenever Mars was in opposition in the last few centuries, it was common practice to compute the length of the astronomical unit (the distance between the Earth and the Sun) on the basis of trigonometric measurements of the distance between Earth and Mars. In 1877, Schiaparelli fell for an optical illusion when he thought he saw trenches and grooves on Mars which he called ‘canali‘. For many of Schiaparelli‘s contemporaries they simply had to be of artificial origin, and even much later, when the scientific world had long recognized the optical illusion for what it was, they led many to believe in an intelligent civilization on our planetary neighbor. Six probes have landed on the planet by now, and although their analyses rule out any form of life on Mars so far, the planet remains the most important destination for international astronautics in its search for existing or extinct life on another celestial body of the Solar System.
| Mass | 6.4185 x 1023 kg |
| Radius | 3,397 km |
| Density | 3.94 g/cm3 |
| Rotation period | 24.62 h |
| Orbital period | 687 days |
| Mean distance from the Sun | 227.9 x 106 km |
Thanks to Mariner 9, Viking 1/2 and, most of all, to recent orbital missions like Mars Express, Mars Global Surveyor and Mars Reconnaissance Orbiter, we are fairly familiar with conditions and formations on the surface. Roughly speaking, the surface of Mars may be subdivided into two large regions: a lowland area in the north and a highland area in the south that features numerous impact craters. Together with its three smaller neighbors Arsia Mons, Ascraeus Mons and Pavonis Mons, Olympus Mons, a shield volcano measuring 24 kilometers in height and 600 kilometers in diameter, forms a highly conspicuous landmark close to the equator, on top of a large rise, 4,000 km in diameter – the Tharsis region. Another outstanding feature is the enormous canyon system of Valles Marineris which is 5,000 kilometers long and up to 200 kilometers wide. The deepest trenches are up to 11 kilometers deep. In the catchment area of the Valles system, a landscape featuring numerous dried-up riverbeds and minor canyons stands out, indicating that water or the ice of glaciers might have been active on Mars in earlier times. Finally, the southern hemisphere harbors two impact craters, Hellas and Argyre. Depending on the seasons, the poles are covered by a thick layer of water and carbon dioxide ice, respectively. Close to the equator, daytime temperatures may rise to +30 degrees centigrade in summer, whereas nighttime temperatures at the poles may drop as low as -140 degrees centigrade in winter. On the equator, the average daytime temperature ranges below the freezing point.
Like that of Venus, the atmosphere of Mars consists predominantly (95 percent) of carbon dioxide (CO2), but the pressure on the surface amounts to no more than six millibar (1,013 millibar on Earth). In the Martian atmosphere, clouds of water vapor may form and tremendous storms may develop in certain seasons. Carrying sand and dust up to a height of 50 kilometers, they distribute the material over the entire planet, causing the sky to take on a yellowish-brown hue and creating clearly visible dune fields. While most dust storms are regionally limited, they may grow to global dimensions every five or ten years.
Last update: 31/05/2010 15:27
