The Grand Canyon on Earth – which is five times shallower and 10 times shorter than the Valles Marineris – was carved by the Colorado River.
But scientists aren't sure what would have formed the 8- to 10-kilometre (5 to 6.2 miles) deep canyon of Valles Marineris and Tithonium Chasma, so they've been taking photos to try and find out.Some researchers suspect a large tectonic "crack" may have split Mars' surface, to be later enhanced by lava flow, or potentially water if the planet's axial tilt was just right.Â