Geologic Features

Mars has a radius of 3,393 km (as compared to Earth's 6,378). Because of this difference in size the interior of Mars cooled much faster than that of the Earth, so it has a lower heat flow and is less active. The axis of Mars is tilted with respect to its orbital plane, so the planet undergoes seasonal changes similar to those on Earth. Surface temperatures of Mars during the summer can reach 273 K though the average is about 50 K cooler. Winter temperatures can be as low as 150 K.

Mars is unusual in that it has global asymmetry about the equator dividing the planet into old and young hemispheres. The southern hemisphere is generally 1 to 3 km above the Martian sea-level, while the northern hemisphere lies below that level. The older terrain in the southern hemisphere is heavily cratered and contains numerous channels kilometers wide. The northern hemisphere has volcanic flows and some craters, but is mostly plains and irregular shaped mesas. The ground on the surface of Mars is permanently frozen down to depths greater than 1 km, as liquid water cannot exist on the surface and ice is only stable at the poles. It also has almost no plate tectonics because the crust is so rigid and static, which contributes to the large growth of volcanoes.