20461 Dioretsa ( dy-ə-RET-sə), provisional designation 1999 LD 31 , is a centaur and damocloid on a retrograde, cometary-like orbit from the outer Solar System. It 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.[1] The highly eccentric unusual object measures approximately 14 kilometers (8.7 miles) in diameter.[4][6] It was named Dioretsa, the word "asteroid" spelled backwards.[1]

Classification and orbit [ edit ]

Dioretsa is a member of the damocloids,[4] with a retrograde orbit and a negative T Jupiter of −1.547. It is also a centaur, as its orbit has a semi-major axis in between that of Jupiter (5.5 AU) Neptune (30.1 AU).[3] The Minor Planet Center lists it as a critical object and (other) unusual minor planet due to an orbital eccentricity of more than 0.5.[5]

It orbits the Sun at a distance of 2.4–45.4 AU once every 116 years and 10 months (42,686 days; semi-major axis of 23.9 AU). Its orbit has an eccentricity of 0.90 and an inclination of 160° with respect to the ecliptic.[3] Its observation arc begins 12 months prior to its official discovery observation, with a precovery taken by Spacewatch at Steward Observatory in June 1998.[1] Currently, its orbit still has an uncertainty of 2.[3]

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]

Naming [ edit ]

The minor planet's name "Dioretsa" is the word "asteroid" spelled backwards, and is the first numbered of currently 99 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).[7]

Physical characteristics [ 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.[6] It has an absolute magnitude of 13.8.[3] As of 2018, Dioretsa's spectral type as well as its rotation period and shape remain unknown.[3][8]