31179 Gongju

31179 Gongju (provisional designation 1997 YR₂) is a stony Nysian asteroid from the inner regions of the asteroid belt, approximately 5 kilometers (3 miles) in diameter. It was discovered on 21 December 1997, by Japanese amateur astronomer Naoto Sato at his Chichibu Observatory near Tokyo, central Japan.^[1] The S-type asteroid has a rotation period of 4.8 hours and possibly an elongated shape.^[3] It was named for the South Korean city of Gongju.^[1]

31179 Gongju

Discovery[1]
Discovered by	N. Sato
Discovery site	Chichibu Obs.
Discovery date	21 December 1997
Designations
MPC designation	(31179) Gongju
Named after	Gongju[1] (South Korean city)
Alternative designations	1997 YR2 · 1989 TM9 1999 CS56
Minor planet category	main-belt[1][2] · (inner) Nysa[3][4]
Orbital characteristics[2]
Epoch 23 March 2018 (JD 2458200.5)
Uncertainty parameter 0
Observation arc	28.39 yr (10,369 d)
Aphelion	2.9123 AU
Perihelion	1.9732 AU
Semi-major axis	2.4427 AU
Eccentricity	0.1922
Orbital period (sidereal)	3.82 yr (1,394 d)
Mean anomaly	192.32°
Mean motion	0° 15m 29.52s / day
Inclination	3.4527°
Longitude of ascending node	81.303°
Argument of perihelion	248.25°
Physical characteristics
Mean diameter	4.675±0.152 km[5][6] 5.04 km (calculated)[3]
Synodic rotation period	4.829±0.001 h[7]
Geometric albedo	0.21 (assumed)[3] 0.353±0.028[5][6]
Spectral type	S (SDSS-MOC)[3][8]
Absolute magnitude (H)	13.4[6] 13.8[2][3]

Orbit and classification

Gongju is a member of the Nysa family (405),^[3][4] the largest asteroid family of the main belt, consisting of stony and carbonaceous subfamilies. The family, named after 44 Nysa, is located near the 3:1 orbital resonance with Jupiter, a depleted zone that separates the inner from the intermediate asteroid belt.^[9]

It orbits the Sun in the inner asteroid belt at a distance of 2.0–2.9 AU once every 3 years and 10 months (1,394 days; semi-major axis of 2.44 AU). Its orbit has an eccentricity of 0.19 and an inclination of 3° with respect to the ecliptic.^[2] The body's observation arc begins with its observations as 1989 TM₉ at ESO's La Silla Observatory in October 1989, more than 8 years prior to its official discovery observation at Chichibu.^[1]

Physical characteristics

Based on the Moving Object Catalog (MOC) of the Sloan Digital Sky Survey, Gongju has a spectral type of a stony S-type asteroid.^[8]

Rotation period

In October 2012, a rotational lightcurve of Gongju was obtained from photometric observations by American astronomer John Ruthroff at the Shadowbox Observatory in Indiana. Lightcurve analysis gave a well-defined rotation period of 4.829 hours with a high brightness amplitude of 0.80 magnitude, indicative of a non-spherical shape (U=3).^[7]

Diameter and albedo

According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Gongju measures 4.675 kilometers in diameter and its surface has an albedo of 0.353,^[5][6] while the Collaborative Asteroid Lightcurve Link assumes an albedo of 0.21 and calculates a diameter of 5.04 kilometers based on an absolute magnitude of 13.8.^[3]

Naming

This minor planet was named after the South Korean city of Gongju, located in Chungcheongnam Province. It has a population of approximately 120,000 and was the capital of Baekje dynasty in the 5th century AD and the seat of the provincial government until 1932.^[1] The official naming citation was published by the Minor Planet Center on 14 May 2014 (M.P.C. 88406).^[10]