Mars

Mars is the fourth planet from the Sun. It appears red from Earth and is sometimes called the Red Planet. The northern half of Mars has volcanic plains and large volcanoes. This makes the surface basaltic. The southern half is also probably basaltic, although the composition is unknown. It is an ancient cratered terrain and is more than 4000 million years old.

A unique feature on the surface of Mars is the Tharsis bulge. It is roughtly 10 km high and 8000 km across. It takes up one quarter of the surface of Mars. The are different hypothesis for the origin of the Tharsis bulge. One says that it is a lava plateau and that it was formed by volcanics. There is a concentration of large volcanoes on the bulge which helps to support this theory. Another theory is that it was formed by uplift due to isostatic compensation for density differences in the mantle. Evidence for this theory is provided from ancient cratered terrain on the bulge and large scale tensional fracturing that has caused the Valles Marineris.

In the past, water was present on Mars. Erosion and dry river systems are seen on parts of Mars. However, water was only present for a short period of time, and very long ago. The canals could be as old as 4 billion years. Mars has permanent ice caps at both of the poles, but the ice is formed by carbon dioxide. These ice caps are layered with ice and dark dust.

moons: 2; names=Phobos and Deimos