Which planet is home to Olympus Mons?

Olympus Mons is on Mars. It is a gigantic shield volcano in the Tharsis volcanic region and is the tallest known planetary mountain in the Solar System by elevation above its surrounding plains.

The volcano rises about 21 kilometers above the Martian surface and stretches roughly 600 kilometers across. Its broad, gently sloping profile was built by repeated eruptions of fluid basaltic lava. Mars lacks Earth-like moving tectonic plates, so volcanic activity could remain concentrated in one location for a very long time.

Astronomers first observed Olympus Mons as a bright surface feature called Nix Olympica, or “Olympic Snow.” The Mariner 9 spacecraft reached Mars in 1971 and confirmed that the feature was a massive volcano. Its summit contains a complex caldera made from several overlapping collapsed craters.

A common mix-up is comparing it directly with Mount Everest: Everest is higher above sea level than Olympus Mons can be measured above a planet-wide datum, but Olympus Mons has far greater total relief and width.