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(415029) 2011 UL21
Discovery [1]
Discovered by Catalina Sky Srvy.
Discovery site Catalina Stn.
Discovery date17 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 arc9379 days (25.68 yr)
Aphelion3.5091  AU (524.95  Gm)
Perihelion0.73606 AU (110.113 Gm)
2.1226 AU (317.54 Gm)
Eccentricity0.65323
3.09 yr (1129.5 d)
110.19 °
0° 19m 7.392s / day
Inclination34.845°
275.60°
284.74°
Earth  MOID0.0185982 AU (2.78225 Gm)
Physical characteristics
Mean diameter
2.5 km [3]
Mass2.1×1013 kg (assumed) [3]
15.8 [2]

(415029) 2011 UL21, provisional designation 2011 UL21, is an Apollo class potentially hazardous asteroid discovered on October 17, 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 October 27, 2011, with an observation arc of 9.6 days. [4]

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] 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). [8]

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. [9] The next largest PHA (based on absolute magnitude) discovered in 2011 is 2011 WO41 with an absolute magnitude of 16.8. [9]

Chronology of close approaches of large near-Earth objects since 1981 (A)
PHA Date Approach distance in lunar distances Abs. mag
( H) 		Diameter (C)
( m) 		Ref (D)
Nominal (B) Minimum Maximum
(143651) 2003 QO104 1981-05-18 2.761 2.760 2.761 16.0 1333–4306 data
2014 LJ21 1989-08-01 7.034 6.843 7.224 16.0 1333–4306 data
4179 Toutatis 1992-12-08 9.399 9.399 9.399 15.30 2440–2450 data
4179 Toutatis 2004-09-29 4.031 4.031 4.031 15.30 2440–2450 data
(159857) 2004 LJ1 2038-11-16 7.719 7.719 7.719 15.4 1746–4394 data
(4953) 1990 MU 2058-06-05 8.986 8.984 8.988 14.1 3199–10329 data
4179 Toutatis 2069-11-05 7.725 7.724 7.725 15.30 2440–2450 data
(52768) 1998 OR2 2079-04-16 4.611 4.611 4.612 15.8 1462–4721 data
(415029) 2011 UL21 2089-06-25 6.936 6.935 6.938 15.7 1531–4944 data
3200 Phaethon 2093-12-14 7.714 7.709 7.718 14.6 4900–5300 data
(52768) 1998 OR2 2127-04-16 6.536 6.510 6.563 15.8 1462–4721 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 AU≈390 LD)
(E) Color codes:   unobserved at close approach   observed during close approach   upcoming approaches

References

  1. ^ a b "MPEC 2011-U39 : 2011 UL21". IAU Minor Planet Center. 28 October 2011. Retrieved 1 November 2011.
  2. ^ a b c d "JPL Small-Body Database Browser: (2011 UL21)". Jet Propulsion Laboratory. Retrieved 8 April 2016. 2012-04-18 last obs (arc=22 years)
  3. ^ a b "Earth Impact Risk Summary: 2011 UL21". NASA/JPL Near-Earth Object Program Office. Archived from the original on 2 November 2011. Retrieved 1 November 2011.
  4. ^ "Observations of small Solar-System bodies". hohmanntransfer. 27 October 2011. Archived from the original on 29 November 2014. Retrieved 4 September 2013. ( 1.5e-06 = 1 in 667,000 chance)
  5. ^ David Morrison (26 October 2011). "Should we be concerned about 2011 UL21". NASA Ask An Astrobiologist. Retrieved 6 November 2011.[ dead link]
  6. ^ "Date/Time Removed". NASA/JPL Near-Earth Object Program Office. Retrieved 6 November 2011.
  7. ^ "2011 UL21 Orbit". Minor Planet Center. Retrieved 17 May 2012. 2012 04 18 (arc=22 years)
  8. ^ "JPL Close-Approach Data: (2011 UL21)". Retrieved 17 May 2012. 2012-04-18 last obs (arc=22 years)
  9. ^ a b "JPL Small-Body Database Search Engine: PHAs and H < 17 (mag)". JPL Solar System Dynamics. Retrieved 20 November 2011.

External links

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