According to astronomers Mike Brown and Konstantin Batygin, the discovery of 2013 SY99 provides additional evidence for the existence of Planet Nine, but Michele Bannister(see 10463), one of the astronomers who reported the discovery of this object, disputes this due to the orientation of the orbit.[1][11]
Its existence was announced in 2016, but the observations were kept private until 2017. It was listed at the Minor Planet Center and the JPL Small-Body Database on 6 April 2017[8] with a three-year observation arc and an epoch 2017 heliocentric orbital period of 17,500 years.[3]Barycentric orbital solutions, however, are more stable for objects on multi-thousand year orbits, and the barycentric period for 2013 SY99 is 19,700 years.[4][n 1]
As of April 2019, its perihelion distance of q=50.029±0.056 AU and semi-major axis a=690±22 AU make 2013 SY99 a possible sednoid, according to the most common definition of the term (q>50 AU, a>150 AU). It is listed as a sednoid by some.[12] However, 2013 SY99 is usually considered to be an extreme trans-Neptunian object and not a sednoid, due to its high eccentricity which makes the heliocentric orbit unstable.[13][n 1] In the heliocentric reference frame, the perihelion is currently rising, and the nominal orbit has a perihelion distance above 50 AU only since October 2018.[14]
2013 SY99 is estimated to be about 250 km (160 mi) in diameter and moderately red in color.[7] In 2052 it will be roughly 20.3 AU (3.04 billion km) from Neptune. It will come to perihelion (closest approach to the Sun) around 2055 when it will be 50 AU (7.5 billion km) from the Sun.[3]
^ abcdeHeliocentric solutions are unstable due to the changing position of Jupiter over Jupiter's 12 year orbit which perturbs the eccentricity of the two-body solution of the Sun+asteroid. Barycentric solutions are more stable for objects that take thousands of years to orbit the Sun. Between epoch 2017 and epoch 2029, the heliocentric orbital period varies from a low of 17400 years "PR= 6.364×106 d (epoch 2017-Nov-16)" to a high of 26100 years "PR= 9.538×106 d (epoch 2023-Nov-16)".
^Bannister, Michele T.; Chen, Ying-Tung; Jakubik, Marian; et al. (October 2016). A new high-perihelion a ~ 700 AU object in the distant Solar System. 48th Meeting of the Division for Planetary Sciences. 16–21 October 2016. Pasadena, California. Bibcode:2016DPS....4811308B. 113.08.
