Valles Marineris. Artwork of an low-angle perspective view of snow and ice on highland areas around Valles Marineris (Mariner Valleys), a massive system of canyons on Mars. Dust storms or mists are seen in the canyons themselves. Valles Marineris is a massive crack in the Martian crust near the equator. The canyons are many hundreds of kilometres long and are several kilometres deep in places, dwarfing similar canyons on Earth. The Martian surface has been extensively mapped by unmanned spacecraft placed in orbit around Mars. Erosion features in the landscape, and data from rovers that have been used to explore the surface, suggest that water once flowed here, shaping these canyons after their formation.