Minor planet category
9 September 2007
8154 days (22.32 yr)
39.20412 AU (5.864853 Tm)
21.11597 AU (3.158904 Tm)
(309239) 2007 RW10, also written (309239) 2007 RW10, is a temporary quasi-satellite of Neptune. Observed from Neptune, it would appear to go around it during one Neptunian year but it actually orbits the Sun, not Neptune.
Discovery, orbit and physical properties
(309239) 2007 RW10 was discovered by the Palomar Distant Solar System Survey on September 9, 2007. At the time of discovery, this minor body was believed to be a Neptune trojan, but it is no longer listed as such. The Jet Propulsion Laboratory classifies (309239) 2007 RW10 as trans-Neptunian object but the Minor Planet Center includes the object among centaurs. It moves in an orbit with an inclination of 36.1°, a semi-major axis of 30.32 AU, and an eccentricity of 0.2996. Herschel-PACS observations indicate that it has a diameter of 247 km.
Quasi-satellite dynamical state and orbital evolution
(309239) 2007 RW10 is currently following a quasi-satellite loop around Neptune. It has been a quasi-satellite of Neptune for about 12,500 years and it will remain in that dynamical state for another 12,500 years. Prior to the quasi-satellite dynamical state, (309239) 2007 RW10 was an L5 trojan and it will go back to that state soon after leaving its current quasi-satellite orbit. Its orbital inclination is the largest among known Neptune co-orbitals. It is also possibly the largest known object trapped in the 1:1 mean-motion resonance with any major planet.
(309239) 2007 RW10 is a dynamically hot (both, high eccentricity and inclination) object that is unlikely to be a primordial Neptune co-orbital. It probably originated well beyond Neptune and was later temporarily captured in the 1:1 commensurability with Neptune.