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Playfair Crater is an impact crater in the Mare Australe quadrangle of Mars, located at 78.1°S latitude and 126.2°W longitude. It is 64.2 km in diameter and was named after John Playfair, and the name was approved in 1973 by the International Astronomical Union (IAU) Working Group for Planetary System Nomenclature (WGPSN). This picture was taken in the spring season on Mars when the temperature was rising. During the winter, much frost accumulates. When the temperature goes up in the spring, the frost disappears in the thin Martian atmosphere and leaves behind the dark ground. The surface appears covered with dark spots when this defrosting process is occurring.〔http://www.jpl.nasa.gov/news/news.php?release=2013-034〕 The dark spots can be seen in some of the pictures below. Wikiplayfair.jpg|Playfair (Martian crater), as seen by CTX camera (on Mars Reconnaissance Orbiter). Dark dots are places where frost has disappeared. Wikiplayfairdefrosting.jpg|Defrosting going on in Playfair crater, as seen by CTX camera (on Mars Reconnaissance Orbiter). Dark areas are where frost has disappeared thereby showing dark ground. Note: this is an enlargement of the previous image of Playfair crater. ==Why craters are 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. 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「Playfair (Martian crater)」の詳細全文を読む スポンサード リンク
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