20461 Dioretsa

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20461 Dioretsa
Discovery [1]
Discovered by LINEAR
Discovery site Lincoln Lab ETS
Discovery date 8 June 1999
MPC designation (20461) Dioretsa
Pronunciation /d.əˈrɛtsə/ dy-ə-RET-sə
Named after
(spelled backwards)[2]
1999 LD31
centaur[1] · damocloid[citation needed]
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 2
Observation arc 2.54 yr (927 days)
Aphelion 45.320 AU
Perihelion 2.4113 AU
23.866 AU
Eccentricity 0.8990
116.59 yr (42,585 days)
0° 0m 30.6s / day
Inclination 160.42°
Jupiter MOID 0.1887 AU
TJupiter -1.5500
Physical characteristics
Dimensions 14±3 km[3]

20461 Dioretsa (/d.əˈrɛtsə/ dy-ə-RET-sə), provisional designation 1999 LD31, is a distant, comet-like minor planet, classified as a highly eccentric centaur with a retrograde orbit, approximately 14 kilometers in diameter.

This centaur was discovered on 8 June 1999, by members of the LINEAR team at the Lincoln Laboratory Experimental Test Site near Socorro, New Mexico, United States.[3][4] It was named Dioretsa, the word "asteroid" spelled backwards.

Classification and orbit[edit]

Dioretsa orbits the Sun at a distance of 2.4–45.3 AU once every 116 years and 7 months (42,585 days). Its orbit has an eccentricity of 0.90 and an inclination of 160° with respect to the ecliptic.[1]

Its observation arc begins 12 months prior to its official discovery observation, with a precovery taken by Spacewatch at Steward Observatory in June 1998.[4] Currently, its orbit still has an uncertainty of 2.[1]

Retrograde orbit[edit]

An inclination of greater than 90° means that a body moves in a retrograde orbit. Dioretsa's orbit is otherwise similar to that of a comet. This has led to speculation that Dioretsa was originally an object from the Oort cloud.[citation needed]

Physical characteristics[edit]

Diameter and albedo[edit]

According to observations made with the 10-meter Keck Telescope, Dioretsa measures 14 kilometers in diameter and its surface has a low albedo of 0.03.[3] It has an absolute magnitude of 13.8.[1]


As of 2017, Dioretsa's spectral type as well as its rotation period and shape remain unknown.[1][5]


The minor planet's name "Dioretsa" is the word "asteroid" spelled backwards, and is the first numbered of currently more than 20 known minor planets with a retrograde motion in the Solar System.[2] The approved naming citation was published by the Minor Planet Center on 1 May 2003 (M.P.C. 48396).[6]


  1. ^ a b c d e f g h "JPL Small-Body Database Browser: 20461 Dioretsa (1999 LD31)" (2000-12-29 last obs.). Jet Propulsion Laboratory. Retrieved 27 June 2017. 
  2. ^ a b Schmadel, Lutz D. (2006). Dictionary of Minor Planet Names – (20461) Dioretsa, Addendum to Fifth Edition: 2003–2005. Springer Berlin Heidelberg. p. 152. ISBN 978-3-540-34360-8. Retrieved 4 April 2016. 
  3. ^ a b c d Harris, Alan W.; Delbó, Marco; Binzel, Richard P.; Davies, John K.; Roberts, Julie; Tholen, David J.; et al. (October 2001). "Visible to Thermal-Infrared Spectrophotometry of a Possible Inactive Cometary Nucleus". Icarus. 153 (2): 332–337. Bibcode:2001Icar..153..332H. doi:10.1006/icar.2001.6687. Retrieved 4 April 2016. 
  4. ^ a b "20461 Dioretsa (1999 LD31)". Minor Planet Center. Retrieved 4 April 2016. 
  5. ^ "LCDB Data for (20461) Dioretsa". Asteroid Lightcurve Database (LCDB). Retrieved 27 June 2017. 
  6. ^ "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 20 May 2016. 

External links[edit]