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.
Mauna Kea on the Hawaiian Islands is an example of similar shield volcanoes on a smaller scale. The extraordinary size of Olympus Mons is likely because does not have tectonic plates. Thus, the crust remained fixed over a hotspot and the volcano continued to discharge lava.
The mountain, as well as a few other of the volcanoes in the Tharsis region, was visible from Earth to 19th century observers. The astronomer Patrick Moore points out that during dust storms, "Schiaparelli had found that his Nodus Gordis and Olympic Snow were almost the only features to be seen.
But only with the Mariner probes could this be confirmed with certainty. After the Mariner 9 probe had photographed it from orbit in 1972, it became clear that the altitude was much greater than that of any mountain found on Earth, and the name was changed to Olympus Mons.
Image credit: NASA