2015 YQ₁ (also written 2015 YQ1) is an Apollo asteroid that is a temporary horseshoe companion to the Earth, the twelfth known Earth horseshoe librator.^[6] It experienced a close encounter with the Earth on 2015 December 22 at 0.0037 AU.

Discovery

2015 YQ₁ was discovered on 2015 December 19 by A. D. Grauer observing with the 1.5-m reflector telescope at the Mount Lemmon Survey.^[7] As of 9 March 2016, it has been observed 64 times with an observation arc of 3 days.^[2]

Orbit and orbital evolution

2015 YQ₁ is currently an Apollo asteroid (Earth-crossing but with a period greater than a year). Its semi-major axis (currently 1.00134 AU) is similar to that of Earth (1.00074 AU), but it has a relatively high eccentricity (0.40398) and low orbital inclination (2.4865°). It alternates between being an Aten asteroid and being an Apollo asteroid. As of 9 March 2016, this object is the 17th known Earth co-orbital and the 12th known object following a horseshoe path with respect to our planet. Asteroid 2015 YQ₁ follows an asymmetrical horseshoe path with respect to our planet; the value of its relative mean longitude oscillates about 180°, but enclosing 0°; its orbital evolution is rather unstable.^[6]

Physical properties

With an absolute magnitude of 28.1 mag, it has a diameter in the range 7–16 meters (for an assumed albedo range of 0.04–0.20, respectively).