Discovered by Mount Lemmon Survey MPC designation 2015 XX169 Semi-major axis 1.00097 AU Aphelion 1.19 m Argument of perihelion 283.587° Asteroid group Apollo asteroid | Discovery date December 9, 2015 Observation arc 363 days Discovered 9 December 2015 Inclination 7.64° Mean anomaly 345.528° Discoverer Mount Lemmon Survey | |
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Minor planet category Apollo asteroid,
Earth crosser | ||
2015 XX169 (also written 2015 XX169) is an Apollo asteroid that is a temporary horseshoe companion to the Earth, the tenth known Earth horseshoe librator. A close encounter with the Earth on 2015 December 14 caused the value of the semi-major axis of 2015 XX169 to drift slowly upwards, and the object evolved from an Aten asteroid to an Apollo asteroid about a year after this close approach.
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Discovery
2015 XX169 was discovered on 2015 December 9 by R. G. Matheny observing with the 1.5-m reflector telescope at the Mount Lemmon Survey. As of 6 December 2016, it has been observed 47 times with an observation arc of 363 days.
Orbit and orbital evolution
2015 XX169 is currently an Apollo asteroid (Earth-crossing but with a period greater than a year). Its semi-major axis (currently 1.00096 AU) is similar to that of Earth (1.00074 AU), but it has a relatively low eccentricity (0.18431) and moderate orbital inclination (7.640°). It alternates between being an Apollo asteroid and being an Aten asteroid, changing dynamical status every 130 years approximately. As of 9 March 2016, this object is the 15th known Earth co-orbital and the 10th known object following a horseshoe path with respect to our planet. Asteroid 2015 XX169 follows an asymmetrical horseshoe path with respect to our planet; the value of its relative mean longitude oscillates about 180°, but enclosing 0°.
Physical properties
With an absolute magnitude of 27.4 mag, it has a diameter in the range 9–22 meters (for an assumed albedo range of 0.20–0.04, respectively).