

The red planet is home to both the highest mountain and the deepest, longest valley in the solar system. Olympus Mons is roughly 17 miles high, about three times as tall as Mount Everest, while the Valles Marinerissystem of valleys — named after the Mariner 9 probe that discovered it in 1971 — can go as deep as 6 miles and runs east-west for roughly 2,500 miles, about one-fifth of the distance around Mars and close to the width of Australia or the distance from Philadelphia to San Diego.