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Geography off Mars

Mars has a reddish-orange color caused by the iron-rich minerals in its soil. A fine-grained reddish dust blankets the planet and can be lifted into the atmosphere when blown by the wind. Martian dust storms range from small "dust devils" to an occasional spectacular event that shrouds the entire planet for months.

One of the most striking features of Mars is Valles Marineris, a system of canyons located along the equator. Valles Marineris is so large it could almost stretch across the entire continental United States. Its depth is equally as impressive, reaching 8 to 10 km in some places.

Another spectacular feature of the Red Planet is Olympus Mons, the tallest volcano in the Solar System. It rises to more than 25 kilometers above the surrounding plains and is more than 600 kilometers in diameter. Three other large volcanoes sit atop a region called Tharsis and rise to similar elevations. Other volcanic landforms on Mars include volcanic cones and lava-covered plains.

One of the most exciting discoveries made at Mars is that liquid water once flowed across the planet's surface. Martian channels, valleys and gullies appear to be the result of water erosion. The most striking of these features are called outflow channels. They seem to have been carved by massive floods that once rushed across the Red Planet's surface.

Many regions of Mars consist of low-lying plains. These flat areas may seem uninteresting, but some of them could be the remnants of an ancient ocean. Images from the Mars Global Surveyor spacecraft reveal that the lowest-lying regions in the northern hemisphere of Mars are among the flattest, smoothest places in the Solar System. Water might have pooled there and deposited a carpet of sediments.

Like other bodies in the Solar System, Mars has many impact craters that were formed by natural objects striking the planet. An interesting aspect of some of these craters is the material that was ejected on impact. Deposits that look like solidified mudflows suggest that water or ice was beneath the surface of Mars when these collisions occurred.

The polar regions of Mars contain stacks of finely-layered deposits up to several kilometers thick. A mixture of water ice and dust probably formed the layers over a very long period of time. It is thought that variations in climate caused the layering by affecting the amount of ice and dust that fell out of the atmosphere. Like annual rings in the trunk of a tree, polar deposits could reveal a wealth of information about martian climate history. Lying atop these layered deposits is a coating of ice. In winter, carbon dioxide condenses out of the martian atmosphere and forms seasonal frost deposits that expand over the planet from the poles.