Discovery date September 21, 2015 Observation arc 342 days Inclination 9.175° Mean anomaly 208.3767° | MPC designation 2015 SO2 Discovered 21 September 2015 Argument of perihelion 290.0678° Discovered by Črni Vrh Observatory | |
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Aphelion 1.10688036 AU (165.586945 Gm) Semi-major axis 0.99892124 AU (149.436491 Gm) Similar (33342) 1998 WT24, WISE J22460757‑0526350, Kepler‑440b, 22P/Kopff, 1566 Icarus | ||
2015 SO2 (also written 2015 SO2) is an Aten asteroid that is a temporary horseshoe companion to the Earth, the ninth known Earth horseshoe librator. Prior to its most recent close encounter with our planet (2015 September 30) it was an Apollo asteroid.
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Discovery
2015 SO2 was discovered on 2015 September 21 by B. Mikuž observing with the 0.6-m f/3.3 Cichocki telescope at the Črni Vrh Observatory in Slovenia. As of 30 November 2015, it has been observed 84 times with an observation arc of 9 days.
Orbit and orbital evolution
2015 SO2 is currently an Aten asteroid (Earth-crossing but with a period less than a year). Its semi-major axis (currently 0.999115 AU) is similar to that of Earth (0.99957 AU), but it has a relatively low eccentricity (0.108105) and moderate orbital inclination (9.181°). Gravitational interaction with Earth causes its orbit to change so that its average period is one year. It alternates between being an Aten asteroid and being an Apollo asteroid, changing dynamical status every 113 years approximately. As of 30 November 2015, this object is the 14th known Earth co-orbital and the 9th known object following a horseshoe path with respect to our planet. Its orbital evolution characterized by alternating horseshoe and quasi-satellite episodes.
Physical properties
With an absolute magnitude of 23.9 mag, it has a diameter in the range 50–111 meters (for an assumed albedo range of 0.04–0.20, respectively).