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Russell (Martian crater)
Russell Crater is a crater found in the Noachis quadrangle of Mars located at 54.9° south latitude and 347.6° west longitude. It is about 139.7 km in diameter and was named after Henry Norris Russell, an American astronomer (1877-1957). Debris flows have been observed on some of the dunes in this crater. Some researchers believe that they may be caused by liquid water. Liquid water could be stable for short periods of time in the summer in the southern hemisphere of Mars. These gully-like debris flows may be due to small amounts of ice melting.〔Reiss, D, R. Jaumann. 2003. Recent debris flows on Mars: Seasonal observations of the Russelll Crater dune field. Geophysical Research Letters: 30, 1321.〕 Another idea is that chunks of dry ice form on the dunes during the cold winter, then slide down in the spring when it is warmer. Experiments have demonstrated that carbon dioxide from the thawing dry ice forms a lubricating layer under pieces of dry ice, making it easy for the process to take place.〔http://www.jpl.nasa.gov/news/news.php?release=2013-200〕〔http://www.space.com/21539-mars-gullies-dry-ice-sleds.html〕
==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）』
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