Mars, as the images issued by the Phoenix probe show us, is not like the Earth: “It is continuous, seamless and sealess,” writes Oliver Morton -Mapping Mars: Science, Imagination, and the Birth of a World. But rising above the Red Planets frequent dust storms is the Olympus Mons -the tallest known volcano and mountain in our solar system. The central edifice of this shield volcano stands 27 kilometers ( 88,580 ft) high above the surface -or three times the elevation of Mount Everest above sea level and 2.6 times the height of Mauna Kea above its base. It is 550 km in width, flanked by steep cliffs, and has a caldera complex that is 85 km long, 60 km wide, and up to 3 km deep with six overlapping pit craters. Its outer edge is defined by an escarpment up to 6 km tall; unique among the shield volcanoes of the Red Planet.