Valley networks are branching networks of valleys on Mars that superficially resemble terrestrial river drainage basins. They are found mainly incised into the terrain of the martian southern highlands, and are typically - though not always - of Noachian age. The individual valleys are typically less than 5 kilometers wide, though they may extend for up to hundreds or even thousands of kilometers across the martian surface.
Branched valley network in Thaumasia quadrangle, as seen by Viking Orbiter. Field of view is roughly 200 km across.
Part of a valley network near Warrego Valles, seen by THEMIS. Length of image is roughly 50 km.
Finer scale valley networks near Candor Chasma, seen by HiRISE (click to zoom). Field of view is roughly 3.5 km across. Surface the valleys are cut into appears to be eroding back.
The Eberswalde delta, seen by MGS. Note the meanders with cutoffs, now seen in inverted relief.
Mars is the fourth planet from the Sun. The surface of Mars is orange-red because it is covered in iron(III) oxide dust, giving it the nickname "the Red Planet". Mars is among the brightest objects in Earth's sky and its high-contrast albedo features have made it a common subject for telescope viewing. It is classified as a terrestrial planet and is the second smallest of the Solar System's planets with a diameter of 6,779 km (4,212 mi). In terms of orbital motion, a Martian solar day (sol) is equal to 24.5 hours and a Martian solar year is equal to 1.88 Earth years. Mars has two natural satellites that are small and irregular in shape: Phobos and Deimos.
Comparison: Earth and Mars
Curiosity's view of Martian soil and boulders after crossing the "Dingo Gap" sand dune
Valles Marineris, taken by the Viking 1 probe
Edge-on view of Mars atmosphere by Viking 1 probe