Discovery date 17 October 2011 Discovered 17 October 2011 | MPC designation 2011 UL21 Observation arc 9379 days (25.68 yr) Absolute magnitude 15.8 | |
Discovered by Catalina Sky Survey (703)0.68-m Schmidt + CCD Aphelion 3.5091 AU (524.95 Gm) (Q) Similar (144898) 2004 VD17, (410777) 2009 FD, 2013 TV135, (308635) 2005 YU55, (29075) 1950 DA | ||
(415029) 2011 UL21 (provisionally known as 2011 UL21) is an Apollo class potentially hazardous asteroid (PHA) discovered on October 17, 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 October 27, 2011 with an observation arc of 9.6 days. (415029) 2011 UL21 briefly had about a 1 in a million chance of impacting in 2029. Its cumulative impact probability was dropped to 1 in 71 million by 2 November 2011 with an observation arc of 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 1.6AU. Palomar Observatory precovery images from 1989 and 1990 have extended the observation arc to 22 years. Its next notable close approach to the Earth will be on June 27, 2024 at a distance of 0.044 AU (6,600,000 km; 4,100,000 mi).
With an absolute magnitude (H) of 15.8, it is potentially the largest/brightest potentially hazardous asteroid 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.