Mars

Mars is similar to Earth in that it has about a twenty‐four‐hour day, an atmosphere, polar ice caps (carbon dioxide), and winter and summer seasons. Unlike Earth, Mars does not have a dipolar magnetic field. To date, no evidence of life has been discovered on the planet.

The northern hemisphere is marked by shield volcanoes and volcanic cones. Craters are widely scattered. These volcanic mountains are three times as high as the tallest volcanic mountains on Earth. Olympus Mons is the largest volcanic structure discovered so far in the solar system. The tremendous size of the volcanoes suggests that the magma sources supplied the volcanic vent for a very long time and that the lithosphere is very strong. Horst and graben fault basins have also been identified. The volcanic activity is thought to be fairly recent, since many of the cones have not been pitted by meteoric impacts (an application of relative time principles). Craters are also rare on the volcano slopes, suggesting the most recent layers of volcanic flows are less than 100 million years old. In contrast, the southern hemisphere is studded with thousands of impact craters and is not as volcanically active.

The Martian surface, weathered and composed of clay and sulfate materials, is shaped by winds that form sand dunes. Meandering braided structures look as though they were formed by running water or gigantic floods. Flooding could occur if the frozen surface were suddenly melted by magmatic activity or a change in climate.