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Lockyer is a crater in the Elysium quadrangle of Mars, located at 28° North and 199.5° West. It is 71 km in diameter and was named after Joseph N. Lockyer, a British astronomer (1836-1920).〔http://planetarynames.wr.usgs.gov/〕 Lockyer is fairly easy to spot on Mars maps because it sits in the relatively young northern hemisphere, where there are few craters. It is close to Elysium Mons and Hecates Tholus, two large volcanoes. Impact craters generally have a rim with ejecta around them, in contrast volcanic craters usually do not have a rim or ejecta deposits. As craters get larger (greater than 10 km in diameter) they usually have a central peak.〔http://www.lpi.usra.edu/publications/slidesets/stones/〕 The peak is caused by a rebound of the crater floor following the impact. Wikilockyer.jpg|Lockyer, as seen by CTX camera (on Mars Reconnaissance Orbiter). Image:Lockyer Crater.JPG|Lockyer's central hills, as seen by HiRISE. Image:layers in Lockyer Crater.jpg|Layers in Lockyer, as seen by HiRISE under the HiWish program. ==Why are craters important?== The density of impact craters is used to determine the surface ages of Mars and other solar system bodies.〔 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「Lockyer (Martian crater)」の詳細全文を読む スポンサード リンク
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