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2014 AA was a small near-Earth asteroid roughly 2–4 meters in diameter that struck Earth on 2 January 2014.〔 It was discovered on 1 January 2014 by Richard Kowalski at the Mount Lemmon Survey at an apparent magnitude of 19 using a reflecting telescope at Mount Lemmon Observatory.〔 2014 AA was only observed over a short observation arc of about 70 minutes,〔 and entered Earth's atmosphere about 21 hours after discovery.〔 ==Entry== Using a poorly determined orbit, the JPL Small-Body Database listed a 3-sigma solution with impact occurring around 2 January 2014 02:33 UT ± 1 hour and 5 minutes.〔 The Minor Planet Center listed impact as occurring around 2 January 2014 05:00 UT ± 10 hours.〔 Independent calculations by Bill Gray, the Minor Planet Center and Steve Chesley at the Jet Propulsion Laboratory have verified that impact was virtually certain.〔 The impactor would have been roughly the size of , which exploded above the Nubian Desert in Sudan on 7 October 2008. Calculations by Chesley suggest the impactor fell somewhere on an arc extending from Central America to East Africa, with a best-fit location just off the coast of West Africa.〔 Calculations by Pasquale Tricarico using the nominal orbit show that 2014 AA entered Earth's shadow cone approximately 40 minutes before entering the atmosphere.〔 Infrasound was detected by three stations of the Comprehensive Nuclear-Test-Ban Treaty Organization.〔 Peter Brown and Petrus Jenniskens located weak signals from infrasound stations in Bolivia, Brazil and Bermuda.〔 2014 AA entered Earth's atmosphere around 04:02 UT〔 3,000 km from Caracas, Venezuela, far from any landmass.〔 No ships or planes have reported witnessing the event.〔 Kowalski previously discovered , the first asteroid discovered before Earth impact, using the same telescope in October 2008.〔 There are about a billion near-Earth objects in the size range of 2014 AA, and impacts of comparably-sized objects occur several times each year.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「2014 AA」の詳細全文を読む スポンサード リンク
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