Valles Marineris. Artwork of an aerial view of Valles Marineris (Mariner Valleys), a massive system of canyons on Mars. Valles Marineris is a massive crack in the Martian crust near the equator. Long slanting shadows are seen falling across the dry and arid landscape of this desert world. 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.