Which is the largest canyon in the solar system?

Valles Marineris stretches about 4,000 km along the Martian equator, a distance similar to the width of the continental United States. It reaches depths of up to about 7 km and is up to 200 km wide in places. By comparison, Arizona's Grand Canyon is about 446 km long and 1.8 km deep. Scientists think Valles Marineris formed mainly as the Martian crust stretched and cracked when the nearby Tharsis volcanic region bulged upwards, rather than being carved by a river. It is named after NASA's Mariner 9 spacecraft, which discovered it in 1971–72.