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(367789) 2011 AG5
(also written 2011 AG5) is a near-Earth asteroid and potentially hazardous object.〔 It has a diameter of about .〔 It was removed from the Sentry Risk Table on 21 December 2012 and as such it now has a rating of 0 on the Torino Scale.〔
It was discovered on 8 January 2011 by the Mt. Lemmon Survey at an apparent magnitude of 19.6 using a reflecting telescope.〔 Pan-STARRS precovery images from 8 November 2010 extended the observation arc to 317 days.〔 Observations by the Gemini telescope at Mauna Kea recovered the asteroid on October 20, 21 and 27, 2012,〔 and extended the observation arc to 719 days.〔 The October 2012 observations have reduced the orbit uncertainties by more than a factor of 60, meaning that the Earth's position in February 2040 no longer falls within the range of possible future paths for the asteroid.〔 On 4 February 2040 the asteroid will pass no closer than (~2.3 LD) from Earth.〔 Until 21 December 2012 it was listed on the Sentry Risk Table with a rating on the Torino Scale of Level 1.〔 A Torino rating of 1 is a routine discovery in which a pass near the Earth is predicted that poses no unusual level of danger.〔 It is estimated that an impact would produce the equivalent of 100 megatons of TNT,〔 roughly twice that of the most powerful nuclear weapon ever detonated (Tsar Bomba). This is powerful enough to damage a region at least a hundred miles wide.
== Older risks ==
Virtual clones of the asteroid that fit the mid-2012 uncertainty region in the known trajectory showed four potential impacts between 2040 and 2047.〔 It had a 1 in 500 chance of impacting the Earth on 5 February 2040.〔 In September 2013, there was an opportunity to make additional observations of 2011 AG5 when it came within of Earth.〔 The 2013 observations allowed a further refinement to the known trajectory. The asteroid will also pass from the Earth on 3 February 2023.〔〔 The 2023 gravitational keyhole was 227 miles (365 kilometers) wide.〔 With a Palermo Technical Scale of -1.00,〔 the odds of impact by were about 10 times less〔 than the background hazard level of Earth impacts which is defined as the average risk posed by objects of the same size or larger over the years until the date of the potential impact.〔
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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