Valles Marineris - Latin for Mariner Valleys, which was named after the Mariner 9 Mars orbiter of 1971-72 which discovered it) This vast canyon system runs along the Martian equator. At more than 4,000 km long, 200 km wide. In places the canyon floor reaches a depth of 10 km, 6 to 7 times deeper than the Grand Canyon. The Valles Marineris rift system is larger than any of Earth's largest canyons - if on earth, would extend all the way across the United States - and is the largest known crevice in the solar system.
Wind-drifted material, mostly dark in color, apparently still moves along the canyon floor and locally forms conspicuous dunes.
The origin of the Valles Marineris remains unknown, although a leading hypothesis holds that it started as a crack billions of years ago as the planet cooled.
