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Olympus Mons (Latin for Mount Olympus) is a very large shield volcano on the planet Mars. By one measure, it has a height of nearly 25 km (16 mi). Olympus Mons stands almost three times as tall as Mount Everest's height above sea level. It is the youngest of the large volcanoes on Mars, having formed during Mars's Amazonian Period. It is currently the largest volcano discovered in the Solar System and had been known to astronomers since the late 19th century as the albedo feature Nix Olympica (Latin for "Olympic Snow"). Its mountainous nature was suspected well before space probes confirmed its identity as a mountain.〔Patrick Moore 1977, ''Guide to Mars'', London (UK), Cutterworth Press, p.96〕 The volcano is located in Mars's western hemisphere at approximately ,〔 just off the northwestern edge of the Tharsis bulge. The western portion of the volcano lies in the Amazonis quadrangle (MC-8) and the central and eastern portions in the adjoining Tharsis quadrangle (MC-9). Two impact craters on Olympus Mons have been assigned provisional names by the International Astronomical Union. They are the -diameter Karzok crater () and the -diameter Pangboche crater ().〔(【引用サイトリンク】 New names on Olympus Mons )〕 The craters are notable for being two of several suspected source areas for shergottites, the most abundant class of Martian meteorites.〔Frankel, C.S. (2005). ''Worlds on Fire: Volcanoes on the Earth, the Moon, Mars, Venus and Io;'' Cambridge University Press: Cambridge, UK, p. 160. ISBN 978-0-521-80393-9.〕 ==Description== As a shield volcano, Olympus Mons resembles in its morphology the large volcanoes making up the Hawaiian Islands. The edifice is about wide.〔("Olympus Mons" ), NASA, retrieved 30 August 2010.〕 Because the mountain is so large, with complex structure at its edges, allocating a height to the structure is difficult. It stands above the Mars global datum, and its local relief, from the foot of the cliffs which form its margin to the northwest to its peak, is nearly 〔 (a little over twice 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 (collapse craters) forming an irregular depression × across〔Mouginis-Mark, P.J.; Harris, A.J.L.; Rowland, S.K. (2007). Terrestrial Analogs to the Calderas of the Tharsis Volcanoes on Mars in ''The Geology of Mars: Evidence from Earth-Based Analogs,'' M. Chapman, Ed.; Cambridge University Press: Cambridge, UK, p. 84〕 and up to deep.〔Carr, M.H. (2006). The Surface of Mars; Cambridge University Press: Cambridge, UK, p. 51.〕 The volcano's outer edge consists of an escarpment, or cliff, up to tall, a feature unique among the shield volcanoes of Mars. Olympus Mons covers an area approximately the size of Arizona, or about .〔Frankel, C.S. (2005). ''Worlds on Fire: Volcanoes on the Earth, the Moon, Mars, Venus and Io;'' Cambridge University Press: Cambridge, UK, p. 132. ISBN 978-0-521-80393-9.〕 Being a shield volcano, Olympus Mons has a very low profile. The average slope on the volcano's flanks is only 5°.〔 Slopes are highest near the middle part of the flanks and grow shallower toward the base, giving the flanks a concave upward profile. The shape of Olympus Mons is distinctly unsymmetrical. Its flanks are shallower and extend out further from the summit in the northwestern direction than they do to the southeast. The volcano's shape and profile have been likened to a "circus tent" held up by a single pole that is shifted off center.〔''ScienceDaily'' (2009). Volcanic Spreading And Lateral Variations In Structure Of Olympus Mons, Mars, Feb. 15. http://www.sciencedaily.com/releases/2009/02/090203175343.htm.〕 Because of the size of Olympus Mons and its shallow slopes, an observer standing on the Martian surface would be unable to view the entire profile of the volcano, even from a great distance. The curvature of the planet and the volcano itself would obscure such a synoptic view.〔Hanlon, M. (2004). ''The Real Mars;'' Constable & Robinson: London, p. 22. ISBN 1-84119-637-1.〕 Similarly, an observer near the summit would be unaware of standing on a high mountain, as the slope of the volcano would extend beyond the horizon, a mere 3 kilometers away.〔(Martian Volcanoes on HST Images ) How Far Could I See Standing on Olympus Mons, "2.37 miles", Jeff Beish, Former A.L.P.O. Mars Recorder 〕 The typical atmospheric pressure at the top of Olympus Mons is 72 pascal, about 12% of the average Martian surface pressure of 600 pascal.〔(Public Access to Standard Temperature-Pressure Profiles ) Standard Pressure Profiles measured by MGS Radio Science team at range from approx 30 to 50 pascals. 〕〔(Late Martian Weather! ) ''stanford.edu'' temperature/pressure profiles 1998 to 2005〕 Both are exceedingly low by terrestrial standards. By comparison, the atmospheric pressure at the summit of Mount Everest is 32,000 pascals, or about 32% of Earth's sea level pressure.〔 〕 Even so, high-altitude orographic clouds frequently drift over the Olympus Mons summit, and airborne Martian dust is still present.〔Hartmann, W.K. ''A Traveler’s Guide to Mars: The Mysterious Landscapes of the Red Planet.'' Workman: New York, 2003, pp. 300.〕 Although the average Martian surface atmospheric pressure is less than one percent of Earth's, the much lower gravity on Mars increases the atmosphere's scale height; in other words, Mars's atmosphere is expansive and does not drop off in density with height as sharply as Earth's. Olympus Mons is an unlikely landing location for automated space probes in the near future. The high elevations preclude parachute-assisted landings because of insufficient atmospheric thickness to slow the spacecraft down. Moreover, Olympus Mons stands in one of the dustiest regions of Mars. A mantle of fine dust covers much of the terrain, obscuring the underlying bedrock (rock samples might be hard to come by). The dust layer would also likely cause severe maneuvering problems for rovers. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Olympus Mons」の詳細全文を読む スポンサード リンク
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