(612095) 1999 OJ4

(612095) 1999 OJ₄ (provisional designation 1999 OJ₄) is a trans-Neptunian object and binary system from the classical Kuiper belt, located in the outermost region of the Solar System. The bright cubewano belongs to the cold population and measures approximately 75 kilometers (47 miles) in diameter. It was first observed at Mauna Kea Observatory on 18 July 1999. Discovered in 2005, its moon is just 3 kilometers smaller than its primary and has an orbital period of 84 days.^[1][6]

(612095) 1999 OJ₄

Orbital diagram of 1999 OJ4
Discovery[1]
Discovered by	Mauna Kea Obs.
Discovery site	Mauna Kea Obs.
Discovery date	18 July 1999
Designations
MPC designation	(612095) 1999 OJ4
Alternative designations	1999 OJ4
Minor planet category	TNO[2] · cubewano[3][4][5] cold
Orbital characteristics[2]
Epoch 27 April 2019 (JD 2458600.5)
Uncertainty parameter 4
Observation arc	9.21 yr (3,363 d)
Aphelion	39.013 AU
Perihelion	37.200 AU
Semi-major axis	38.107 AU
Eccentricity	0.0238
Orbital period (sidereal)	235.24 yr (85,921 d)
Mean anomaly	294.62°
Mean motion	0° 0m 15.12s / day
Inclination	3.9954°
Longitude of ascending node	127.44°
Argument of perihelion	285.68°
Known satellites	1 (D: 72 km; P: 84.12 d)[6]
Physical characteristics
Mean diameter	75 km[3]
Mass	(0.4045±0.0063)×1018 kg (system)[7]
Geometric albedo	0.1 (assumed)[8] 0.225[3][9]
Spectral type	B–V = 1.68[3][4] V–R = 0.682[4]
Absolute magnitude (H)	7.1[1][2]

Orbit and classification

1999 OJ₄'s orbit characterizes it as a classical Kuiper Belt object, or cubewano. Due to its nearly circular orbit and low inclination, it is also in the "cold" population of cubewanos. As a result, it is likely reddish in color.^[10][11]

Satellite

1999 OJ₄ has one moon. This moon was discovered by the Hubble Space Telescope^[9] on 5 October 2013. It orbits 3306±17 km away from 1999 OJ₄, completing one orbit every 84.1147±0.0050 d. The orbit has an eccentricity of 0.3683±0.0038.^[7]

At about 72 km, it is nearly the same size as 1999 OJ₄. From the surface of 1999 OJ₄, it would have an apparent diameter of roughly 8.11°,^[a] over fourteen times the apparent size of the Sun from Earth.

Notes

1. Calculated by solving ${\displaystyle \scriptstyle {\mathrm {tan} \left({\frac {\theta }{2}}\right)={\frac {\mathrm {radius~of~moon} }{\mathrm {distance~from~surface~of~asteroid~to~center~of~moon} }}}}$.