Olympus Mons the height of Mauna Kea as measured from its base on the ocean floor). The total elevation change from the plains of Amazonis Planitia, over to the northwest, to the summit approaches . The summit of the mountain has six nested calderas (collapsed craters) forming an irregular depression × across and up to deep. The volcano's outer edge consists of an escarpment, or cliff, up to tall (although obscured by lava flows in places), a feature unique among the shield volcanoes of Mars. Olympus Mons covers an area of about , which is approximately the size of Italy, and it
Solar System 7 light-years away. Compared to many other planetary systems, the Solar System stands out in lacking planets interior to the orbit of Mercury. The known Solar System also lacks super-Earths (Planet Nine could be a super-Earth beyond the known Solar System). Uncommonly, it has only small rocky planets and large gas giants; elsewhere planets of intermediate size are typical—both rocky and gas—so there is no "gap" as seen between the size of Earth and of Neptune (with a radius 3.8 times as large). Also, these super-Earths have closer orbits than Mercury. This led to hypothesis that all planetary systems start