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2007 WD5
is an Apollo asteroid some in diameter〔(【引用サイトリンク】url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2007wd5 )〕 and a Mars-crosser asteroid discovered on November 20, 2007, by Andrea Boattini of the Catalina Sky Survey. Early observations of 2007 WD5 caused excitement amongst the scientific community when it was estimated as having as high as a 1 in 25 chance of colliding with Mars on January 30, 2008.〔 However, by January 9, 2008, additional observations allowed NASA's Near Earth Object Program (NEOP) to reduce the uncertainty region resulting in only a 1-in-10,000 chance of impact.〔 most likely passed Mars at a distance of 6.5 Mars radii. Due to this relatively small distance and the uncertainty level of the prior observations, the gravitational effects of Mars on its trajectory are unknown and, according to Steven Chesley of NASA's Jet Propulsion Laboratory Near-Earth Object program, is currently considered 'lost' (see lost asteroids).
==Discovery==
The asteroid was discovered on November 20, 2007 by Andrea Boattini of the NASA-funded Catalina Sky Survey on Mount Lemmon, near Tucson, Arizona, USA, using a 1.5-meter telescope. It was discovered in the constellation Taurus at an apparent magnitude of +20. This is about 400,000 times fainter than most people can see with the naked eye on a dark night far from city lights.〔 It was discovered nineteen days after passing near the Earth. By the time it arrived at Mars it had an apparent magnitude of roughly +26 and therefore appeared over 100x fainter than at the time of discovery.〔Horizons Brightness Difference between 11-20-07 and 01-30-08: (5th root of 100) ^ (@marsJan30th APmag 25.9 - DiscoveryNov20th APmag 20.2) = 190x〕
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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