Mount Olympus is a shield volcano on Mars. It has a height of nearly 25 km, almost three times as tall as Mount Everest. It is the youngest of three vomcanos and has been known to astronomers since the late 19th century, well before space probes. Mariner 9 spacecraft arrived in orbit around Mars in 1971 during a global dust-storm and confirmed that the mountain was a volcano before naming it after the Greek mount.