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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]
| Discovery [1] | |
|---|---|
| Discovered by | N. Sato |
| Discovery site | Chichibu Obs. |
| Discovery date | 21 December 1997 |
| Designations | |
| (31179) Gongju | |
Named after | Gongju [1] (South Korean city) |
| 1997 YR2 · 1989 TM9 1999 CS56 | |
| 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 |
| 2.4427 AU | |
| Eccentricity | 0.1922 |
| 3.82 yr (1,394 d) | |
| 192.32° | |
| 0° 15m 29.52s / day | |
| Inclination | 3.4527° |
| 81.303° | |
| 248.25° | |
| Physical characteristics | |
| 4.675±0.152 km[5][6] 5.04 km (calculated)[3] | |
| 4.829±0.001 h[7] | |
| 0.21 (assumed)[3] 0.353±0.028[5][6] | |
| S (SDSS-MOC)[3][8] | |
| 13.4[6] 13.8[2][3] | |
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]
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]
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]
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