Thanks to the many images taken by the probes sent there in recent decades, we know that Mars has multiple interesting geographic features . The most important is the great difference that is observed between its northern and southern hemispheres : most of the northern half has a lower elevation than the southern (up to six kilometers lower). It also has far fewer impact craters, and is much smoother and more uniform throughout. In addition, the crust of the northern hemisphere appears to be much thinner than that of the southern hemisphere. While astronomers are unsure why this dichotomy occurs, it involves the three main forces that have influenced the nature of the Martian surface: volcanism, tectonic activity, and impacts.
Some of the most striking features on the surface of Mars are its mountains, all of them dormant volcanoes . The western edge of the southern hemisphere contains two different areas, the Tharsis bulge and the Elysium volcanic complex, each containing several volcanoes. The Tharsis bulge covers about 25% of the planet’s surface and rises seven to ten kilometers above it. This includes Mount Olympus, the largest mountain in the Solar System.
Until a few years ago, scientists were sure that Mars did not have plate tectonics like Earth. It was later discovered that tectonic forces do indeed operate . Not only landforms such as steep cliffs and vertical canyon walls evidence the existence of fully active faults, but also the fact that volcanoes on Mars are concentrated in two different areas.
The huge valley system known as Valles Marineris is the deepest in the Solar System, occupying a quarter of the planet’s circumference. It is also a plate boundary, with horizontal movement. With only one known fault, unlike the many recorded on Earth, some believe that the Mars tectonic system is much younger than ours .
Impact craters and basins are common in the southern hemisphere. The Hellas basin is the largest of them all, at 1,800 kilometers in diameter. The largest sinkholes are believed to date back to a period of heavy bombardment, about 3.8 billion years ago. They show signs of erosion and also contain a lot of regolith or soil deposits. The smaller craters are younger and look a lot like those on the Moon.
Mars has many different types of craters thanks to erosion, deposits, and volcanic activity. They also contain ejection blankets, flows that form on the ground after an impact melts the ice below the planet’s surface, which normally melts and refreezes according to changes in temperature. There are also caps at the poles, the extent of which changes with the seasons.
Because Mars has a similar tilt to Earth, it enjoys four seasons, longer and of varying duration . Temperatures drop to -143ºC in the polar caps during winter.
The atmospheric pressure on Mars is, as has also been said before, much lower than that of Earth and its atmosphere so thin that it barely blocks the incidence of heat on the surface . There are ice clouds, probably caused when the wind raises dust; in fact, one of the most important climatic features of the red planet is dust storms , which can last up to a month.
