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Main Crater is an impact crater in the Mare Australe quadrangle of Mars, located at 76.6°S latitude and 310.9°W longitude. It is 109.0 km in diameter and was named after Rev. Robert Main, and the name was approved in 1973 by the International Astronomical Union (IAU) Working Group for Planetary System Nomenclature (WGPSN). The floor of Main shows dark portions which are caused by pressurized carbon dioxide blowing dust in the atmosphere in the spring when the temperature goes up. Some of the dust is shaped into streaks if there is a wind.
Many ideas have been advanced to explain these features. These features can be seen in some of the pictures below.
Close up views of these features often reveal fuzzy features that have been named "spiders."