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Copernicus is a large crater on Mars, with a diameter close to 300 km. It is located south of the planet's equator in the heavily cratered highlands of Terra Sirenum in the Phaethontis quadrangle at 48.8°S and 191.2°E. Its name was approved in 1973, and it was named after Nicolaus Copernicus. The impact that formed Copernicus likely occurred more than 3 billion years ago. The crater contains smaller craters within its basin and is particularly notable for gully formations that are presumed to be indicative of past liquid water flows. Many small channels exist in this area; they are further evidence of liquid water. On the basis of their form, aspects, positions, and location amongst and apparent interaction with features thought to be rich in water ice, many researchers believed that the processes carving the gullies involve liquid water. However, this remains a topic of active research. As soon as gullies were discovered,〔Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.〕 researchers began to image many gullies over and over, looking for possible changes. By 2006, some changes were found.〔Malin, M., K. Edgett, L. Posiolova, S. McColley, E. Dobrea. 2006. Present-day impact cratering rate and contemporary gully activity on Mars. Science 314, 1573_1577.〕 Later, with further analysis it was determined that the changes could have occurred by dry granular flows rather than being driven by flowing water.〔Kolb, et al. 2010. Investigating gully flow emplacement mechanisms using apex slopes. Icarus 2008, 132-142.〕〔McEwen, A. et al. 2007. A closer look at water-related geological activity on Mars. Science 317, 1706-1708.〕〔Pelletier, J., et al. 2008. Recent bright gully deposits on Mars wet or dry flow? Geology 36, 211-214.〕 With continued observations many more changes were found in Gasa Crater and others.〔NASA/Jet Propulsion Laboratory. "NASA orbiter finds new gully channel on Mars." ScienceDaily. ScienceDaily, 22 March 2014. http://www.sciencedaily.com/releases/2014/03/140322094409.htm〕 With more repeated observations, more and more changes have been found; since the changes occur in the winter and spring, experts are tending to believe that gullies were formed from dry ice. Before-and-after images demonstrated the timing of this activity coincided with seasonal carbon-dioxide frost and temperatures that would not have allowed for liquid water. When dry ice frost changes to a gas, it may lubricate dry material to flow especially on steep slopes.〔http://www.jpl.nasa.gov/news/news.php?release=2014-226〕〔http://hirise.lpl.arizona.edu/ESP_032078_1420〕〔http://www.space.com/26534-mars-gullies-dry-ice.html?cmpid=557882〕 In some years frost, perhaps as thick as 1 meter. Wikicopernicus.jpg|Eastern edge of Copernicus Crater (Martian Crater), as seen by CTX camera (on Mars Reconnaissance Orbiter). Wikicopernicusdevils.jpg|Dust devil tracks on floor of Copernicus Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter). Note: this is an enlargement of the previous image of the eastern edge of Copernicus. Wikicopernicusgullies.jpg|Gullies in small crater on rim of Copernicus Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter). Note: this is an enlargement of a previous image of the eastern edge of Copernicus. Wikicopernicuschannels.jpg|Channels on the floor of Copernicus Crater, as seen by CTX Wikicopernicusdikes.jpg|Possible dikes on floor of Copernicus Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter). The straight lines may be dikes, faults, or joints. == See also == * Planetary nomenclature * Impact crater * List of craters on Mars * Water on Mars * Climate of Mars * Martian Gullies 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「Copernicus (Martian crater)」の詳細全文を読む スポンサード リンク
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