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2011 BT15
(also written 2011 BT15) is a near-Earth asteroid and potentially hazardous object.〔 In 2013 it had the 5th highest impact threat on the Palermo Technical Impact Hazard Scale.〔 It was discovered on 24 January 2011 by Pan-STARRS at an apparent magnitude of 22 using a Ritchey–Chrétien telescope.〔 It has an estimated diameter of .〔 It was removed from the Sentry Risk Table on 17 June 2013.〔
Before the 2013 recovery it had an observation arc of 41 days with an uncertainty parameter of 7. Due to precovery images from 2007 it now has an observation arc of more than 5 years.〔 It makes close approaches to Earth and Mars.〔 While listed on the Sentry Risk Table, virtual clones of the asteroid that fit the uncertainty region in the known trajectory showed a 1 in 71,000 chance that the asteroid could impact Earth on 5 January 2080.〔 With a 2080 Palermo Technical Scale of −3.58,〔 the odds of impact by in 2080 were about 3800 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.〔 JPL Horizons shows that the nominal pass will be on 17 January 2080 at a distance of from Earth.〔 passed from Earth on 28 December 2013.〔 The December 2013 passage was studied by the Goldstone Deep Space Network and further refined the orbit.〔
== References ==
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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