Valles Marineris. Artwork of an aerial view of Valles Marineris (Mariner Valleys), a massive system of canyons near the equator on Mars. The entire canyon system is some 4000 kilometres long, 200 kilometres wide and up to 7 kilometres deep, dwarfing similar canyons on Earth. The surface of Mars has been extensively mapped by orbiting unmanned spacecraft. Erosion features in the landscape, and data from rovers exploring the surface, suggest that water once flowed here, shaping these canyons after their formation.