(415029) 2011 UL21
an Apollo class asteroid
(415029) 2011 UL21 is an Apollo-class potentially hazardous asteroid discovered on 17 October 2011, by the Catalina Sky Survey project. The asteroid is estimated to have a diameter of 2.5 kilometres (1.6 mi). It was rated at Torino scale 1 on 27 October 2011, with an observation arc of 9.6 days. 2011 UL21 is the largest asteroid ever to be rated above a 0 on the Torino scale.
Description
2011 UL21 briefly had about a 1 in a million chance of impacting in 2029. Its cumulative impact probability dropped to 1 in 71 million by 2 November 2011 when the observation arc reached 15 days. It was removed from the Sentry risk table on 4 November 2011 when all impact scenarios for the next 100 years or more were ruled out. During 2029, the closest approach to Earth is 1.6 AU. Palomar Observatory precovery images from 1989 and 1990 have extended the observation arc to 22 years.
With an absolute magnitude of 15.8, it is one of the brightest and therefore largest potentially hazardous asteroids (PHA) detected since (242450) 2004 QY2. The next largest PHA (based on absolute magnitude) discovered in 2011 is 2011 WO41 with an absolute magnitude of 16.8.
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This entry incorporates text from “(415029) 2011 UL21” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.