2015 YU9

2015 YU₉, also known as 2015 YB^[a] and WY032FF, is a sub-kilometer Hungaria asteroid from the inner region of the asteroid belt, approximately 350 meters in diameter. It was first observed on 16 December 2015, by the Catalina Sky Survey at Mount Lemmon Observatory in Arizona, United States.^[2]

2015 YU₉

Discovery[1][2]
Discovered by	CSS
Discovery site	Mount Lemmon Obs.
Discovery date	16 December 2015
Designations
MPC designation	2015 YU9
Alternative designations	2015 YB (deleted)[1][2][a] WY032FF
Minor planet category	main-belt (inner)[1] · Hungaria[3]
Orbital characteristics[1][4]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 5
Observation arc	(32 days)
Aphelion	2.0210 AU
Perihelion	1.7786 AU
Semi-major axis	1.8998 AU
Eccentricity	0.0638
Orbital period (sidereal)	2.62 yr (956 days)
Mean anomaly	231.75°
Mean motion	0° 22m 35.04s / day
Inclination	20.031°
Longitude of ascending node	236.54°
Argument of perihelion	208.74°
Physical characteristics
Dimensions	0.35 km (est. at 0.3)[5]
Absolute magnitude (H)	19.228[1]

Description

Orbit

2015 YU₉ is a member of the dynamical Hungaria group, which form the innermost dense concentration of bright asteroids in the Solar System.^[3] It orbits the Sun at a distance of 1.8–2.0 AU once every 2 years and 7 months (956 days). Its orbit has an eccentricity of 0.06 and an inclination of 20° with respect to the ecliptic.^[1]

Discovery

Precovery images were taken by Pan-STARRS on 8 December 2015.^[2][3] At the time of discovery the asteroid was 0.8 AU (120,000,000 km; 74,000,000 mi) from Earth which is close to the Earth minimum orbit intersection distance (MOID).^[4] The asteroid came to perihelion (closest approach to the Sun) around 28 December 2015.^[4]

When the asteroid was first detected and it had an observation arc less than 1 day, the asteroid was suspected of being a Near-Earth asteroid that would make a close approach to Earth on 19 December 2015.^[a] But that orbit solution used an erroneous observation from the Catalina Sky Survey causing an incorrect orbit determination.^[3] The asteroid is not a near-Earth object.

Diameter and albedo

With an absolute magnitude of 19.2, the inner main-belt asteroid is approximately 350 meters in diameter, based on an assumed albedo of 0.3 – a typical compromise value between 0.4 and 0.2, corresponding to the Hungaria asteroids both as family and orbital group.^[5]

Incorrect media reports

Initial mass media reports for the size of the asteroid were incorrectly based on the assumption the asteroid was 0.02 AU from Earth and not 0.8 AU from Earth.^{[citation needed]} On 31 December 2015 the asteroid received the provisional designation 2015 YU₉.

Notes

1. Archived JPL Small Body Data Base, of JPL solution #1 for asteroid 2015 YB on 17 December 2015 with an observation arc of less than a 1 day. This database entry has been deleted since.