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| OUR SUN | MERCURY | VENUS | EARTH | MARS |
| JUPITER | SATURN | URANUS | NEPTUNE | PLUTO |
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MARS
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Mars orbits the Sun once every 687 days. Like the Earth, it is a rocky planet, but its radius is only 3,390 km, about 50 percent of Earth's radius and its density is significantly less. The length of day on Mars is 24 hours 37 minutes. The tilt of the pole is an Earth-like 24 degrees, making the seasons of Mars similar to ours but about twice as long.
To the naked eye, Mars is a reddish object whose brightness can vary. Through a telescope, Mars resolves into bright orange regions and darker, less red areas whose outlines and tones change with Martian seasons. Conspicuous bright caps, apparently of frost or ice, mark the poles. The reddish colour of the planet is due to the heavily oxidised nature of the surface. The darker areas are believed to consist of weathered and oxidised rocks similar to terrestrial basalts. The surface in the brighter areas seem to contain a large proportion of considerably more weathered and much finer-grained material.
Mars has a very thin, very cold carbon dioxide atmosphere, with small amounts of nitrogen, water vapour, and other trace constituents, including oxygen and noble gases such as argon. Surface temperatures vary greatly with time of day, season, and latitude. Average daily temperatures at the surface do not exceed -30 degrees, and daily variations of -170 degrees are common due to the thinness of the atmosphere. The amount of water vapour is very small and variable. All in all, Mars is a very cold, extreme-altitude desert. Surface pressures are too low and surface temperatures too cold for water to exist.
At certain seasons, Mars is subjected to very strong winds that can move sand and suspend dust in the atmosphere. A major annual event occurs between late spring and early summer in the southern hemisphere. Dust storms develop. Some reach global proportions, producing a yellowish pall that obscures the planet's surface for weeks or even months.
Geologically, Mars is a diversified planet. Much of the southern hemisphere consist of old cratered terrain, probably dating back to the first half billion years of Mars history. By contrast, much of the northern hemisphere is covered by a much less cratered surface believed to consist of volcanic flows. Convincing volcanic features abound proving that the planet has gone through an episode of significant internal activity.
Last modified : GMT