premise: Valles Marineris is on Mars.
hypothesis: Mars . Mars is the site of Olympus Mons , the largest volcano and second-highest known mountain in the Solar System , and of Valles Marineris , one of the largest canyons in the Solar System . Valles Marineris ( Latin for Mariner Valleys , named after the Mariner 9 Mars orbiter of 1971 -- 72 which discovered it ) is a system of canyons that runs along the Martian surface east of the Tharsis region . Valles Marineris is located along the equator of Mars , on the east side of the Tharsis Bulge , and stretches for nearly a quarter of the planet 's circumference .