(415029) 2011 UL21
Apollo class asteroid
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(415029) 2011 UL21, provisional designation 2011 UL21, is an Apollo class potentially hazardous asteroid discovered on 17 October 2011, by the Catalina Sky Survey project.[1] 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.[4] 2011 UL21 is the largest asteroid ever to be rated above a 0 on the Torino Scale.
| |
| Discovery[1] | |
|---|---|
| Discovered by | Catalina Sky Srvy. |
| Discovery site | Catalina Stn. |
| Discovery date | 17 October 2011 |
| Designations | |
| (415029) 2011 UL21 | |
| 2011 UL21 | |
| Apollo · NEO · PHA[2] | |
| Orbital characteristics[2] | |
| Epoch 13 January 2016 (JD 2457400.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 9379 days (25.68 yr) |
| Aphelion | 3.5091 AU (524.95 Gm) |
| Perihelion | 0.73606 AU (110.113 Gm) |
| 2.1226 AU (317.54 Gm) | |
| Eccentricity | 0.65323 |
| 3.09 yr (1129.5 d) | |
| 110.19° | |
| 0° 19m 7.392s / day | |
| Inclination | 34.845° |
| 275.60° | |
| 284.74° | |
| Known satellites | 1 moonlet discovered |
| Earth MOID | 0.0185982 AU (2.78225 Gm) |
| Physical characteristics | |
| 2.5 km[3] | |
| Mass | 2.1Ã1013 kg (assumed)[3] |
| 15.8[2] | |
Description
2011 UL21 briefly had about a 1 in a million chance of impacting in 2029.[5] 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.[6] 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.[7]
With an absolute magnitude of 15.8,[2] it is one of the brightest and therefore largest potentially hazardous asteroids (PHA) detected since (242450) 2004 QY2.[8] The next largest PHA (based on absolute magnitude) discovered in 2011 is 2011 WO41 with an absolute magnitude of 16.8.[8]
On 27 June 2024 it had a relatively close fly-by with the Earth, reaching a minimum distance of 0.044 AU (6,600,000 km; 4,100,000 mi) from it.[9][10] It was revealed to be orbited by a moonlet.[11]
| PHA | Date | Approach distance in lunar distances | Abs. mag (H) |
Diameterâ(C) (m) |
Refâ(D) | ||
|---|---|---|---|---|---|---|---|
| Nominalâ(B) | Minimum | Maximum | |||||
| (143651) 2003 QO104 | 1981-05-18 | 2.761 | 2.760 | 2.761 | 16.0 | 1333â4306 | data |
| 2014 LJ21 | 1989-08-01 | 7.034 | 6.843 | 7.224 | 16.0 | 1333â4306 | data |
| 4179 Toutatis | 1992-12-08 | 9.399 | 9.399 | 9.399 | 15.30 | 2440â2450 | data |
| 4179 Toutatis | 2004-09-29 | 4.031 | 4.031 | 4.031 | 15.30 | 2440â2450 | data |
| (159857) 2004 LJ1 | 2038-11-16 | 7.719 | 7.719 | 7.719 | 15.4 | 1746â4394 | data |
| (4953) 1990 MU | 2058-06-05 | 8.986 | 8.984 | 8.988 | 14.1 | 3199â10329 | data |
| 4179 Toutatis | 2069-11-05 | 7.725 | 7.724 | 7.725 | 15.30 | 2440â2450 | data |
| (52768) 1998 OR2 | 2079-04-16 | 4.611 | 4.611 | 4.612 | 15.8 | 1462â4721 | data |
| (415029) 2011 UL21 | 2089-06-25 | 6.936 | 6.935 | 6.938 | 15.7 | 1531â4944 | data |
| 3200 Phaethon | 2093-12-14 | 7.714 | 7.709 | 7.718 | 14.6 | 4900â5300 | data |
| (52768) 1998 OR2 | 2127-04-16 | 6.536 | 6.510 | 6.563 | 15.8 | 1462â4721 | data |
| (A) This list includes near-Earth approaches of less than 10 lunar distances (LD) of objects with H brighter than 16. (B) Nominal geocentric distance from the center of Earth to the center of the object (Earth has a radius of approximately 6,400 km). (C) Diameter: estimated, theoretical mean-diameter based on H and albedo range between X and Y. (D) Reference: data source from the JPL SBDB, with AU converted into LD (1 AUâ390 LD) (E) Color codes: unobserved at close approach observed during close approach upcoming approaches | |||||||
See also
- 2024 MK â a near-Earth object that made a close approach on 29 June 2024
