What is the name of the largest canyon in the solar system?

The largest canyon in the solar system is Valles Marineris, a vast system of interconnected chasms on Mars.

Valles Marineris stretches more than 4,000 kilometres across the Martian surface, roughly a quarter of the planet’s circumference. It can reach about 200 kilometres in width and up to 7 kilometres in depth, making it dramatically larger than Earth’s Grand Canyon. The system lies near Mars’s equator, east of the Tharsis volcanic region.

Its name means “Mariner Valleys,” honouring NASA’s Mariner 9 spacecraft. When Mariner 9 entered orbit around Mars in 1971, it became the first spacecraft to orbit another planet and revealed the canyon system in detail. Scientists think it formed mainly through immense crustal fracturing associated with the rise of the Tharsis region, later modified by landslides, erosion and possible ancient water activity.

A common mix-up is Coprates Chasma, which is not a competing canyon elsewhere: it is one of the major chasms within Valles Marineris. Hellas Planitia, by contrast, is a giant impact basin, not a canyon.