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Crommlin Crater is an impact crater in the Oxia Palus quadrangle of Mars. It is located at 5.1° north and 10.2° west. It was named after Andrew C. Crommlin, a British astronomer (1865–1939).〔http://planetarynams.wr.usgs.gov〕 Parts of Crommlin crater display many thin layers. These may reflect different climates in the past--some of which were much wetter. Many places on Mars show rocks arranged in layers. Rock can form layers in a variety of ways. Volcanoes, wind, or water can produce layers. Many craters once contained lakes. 〔 Cabrol, N. and E. Grin. 2001. The Evolution of Lacustrine Environments on Mars: Is Mars Only Hydrologically Dormant? Icarus: 149, 291-328.〕 〔 Fassett, C. and J. Head. 2008. Open-basin lakes on Mars: Distribution and implications for Noachian surface and subsurface hydrology. Icarus: 198, 37-56.〕 〔 Fassett, C. and J. Head. 2008. Open-basin lakes on Mars: Implications of valley network lakes for the nature of Noachian hydrology. 〕 Because some crater floors show deltas, we know that water had to be present for some time. Dozens of deltas have been spotted on Mars. 〔 Wilson, J. A. Grant and A. Howard. 2013. INVENTORY OF EQUATORIAL ALLUVIAL FANS AND DELTAS ON MARS. 44th Lunar and Planetary Science Conference. 〕 Deltas form when sediment is washed in from a stream entering a quiet body of water. It takes a bit of time to form a delta, so the presence of a delta is exciting; it means water was there for a time, maybe for many years. Primitive organisms may have developed in such lakes; hence, some craters may be prime targets for the search for evidence of life on the Red Planet. 〔 Newsom H. , Hagerty J., Thorsos I. 2001. Location and sampling of aqueous and hydrothermal deposits in martian impact craters. Astrobiology: 1, 71-88.〕 Wikicrommlin.jpg|Crommlin Crater with important parts labeled, as seen by CTX camera (on Mars Reconnaissance Orbiter). Wikicrommlinlayers.jpg|Layers in mound of Crommlin Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter). Note: this is an enlargement of previous image. Image:Crommlin Crater.JPG|Crommlin Crater Layered Deposit, as seen by HiRISE. The color blue in the photo is a false color. Image:Moundshigh.jpg|Crommlin Crater contains a layered mound that is higher than its rim. This drawing shows how it was formed when much of the material was eroded away. ==Why are Craters important?== The density of impact craters is used to determine the surface ages of Mars and other solar system bodies. 〔 http://www.lpi.usra.edu/publications/slidesets/stones/ 〕 The older the surface, the more craters present. Crater shapes can reveal the presence of ground ice. The area around craters may be rich in minerals. On Mars, heat from the impact melts ice in the ground. Water from the melting ice dissolves minerals, and then deposits them in cracks or faults that were produced with the impact. This process, called hydrothermal alteration, is a major way in which ore deposits are produced. The area around Martian craters may be rich in useful ores for the future colonization of Mars. 〔http://www.indiana.edu/~sierra/papers/2003/Patterson.html.〕 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「Crommlin (crater)」の詳細全文を読む スポンサード リンク
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