_Niinoama.png) Shape model ofNiinoama from itslightcurve | |
| Discovery [1] | |
|---|---|
| Discovered by | A. Natori T. Urata |
| Discovery site | JCPM Yakiimo Stn. |
| Discovery date | 15 August 1991 |
| Designations | |
| (4959) Niinoama | |
Named after | Taira no Tokiko (Imperial House of Japan)[2] |
| 1991 PA1 · 1958 TZ 1966 CB · 1968 MC 1972 EB · 1979 OU13 1980 TG1 · 1980 TS8 1984 OO · 1985 OD 1986 VS1 · 1989 FE1 | |
| main-belt · (outer) [3] background | |
| Orbital characteristics [1] | |
| Epoch 4 September 2017 (JD 2458000.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 67.15 yr (24,528 days) |
| Aphelion | 3.1759AU |
| Perihelion | 3.1272 AU |
| 3.1516 AU | |
| Eccentricity | 0.0077 |
| 5.59yr (2,044 days) | |
| 129.49° | |
| 0° 10m 34.32s / day | |
| Inclination | 8.9913° |
| 128.79° | |
| 320.53° | |
| Physical characteristics | |
| 26.50±0.73 km[4] 27.96±2.4 km[5] 35.842±0.117 km[6] 36.21±0.80 km[7] 42.507±0.576 km[8] | |
| 4.73±0.01 h[9] | |
| 0.0468±0.0109[8] 0.066±0.003[7] 0.079±0.010[6] 0.1081(derived)[3] 0.1082±0.021[5] 0.120±0.014[4] | |
| C(assumed)[3] | |
| 10.8[3][4][5][7][8] · 10.9[1] | |
4959 Niinoama (prov. designation:1991 PA1) is a darkbackground asteroid from the outer regions of theasteroid belt. It was discovered by Japanese astronomersAkira Natori andTakeshi Urata atJCPM Yakiimo Station on 15 August 1991.[10] The presumed carbonaceousC-type asteroid has arotation period of 4.7 hours and measures approximately 36 kilometers (22 miles) in diameter. It was named afterTaira no Tokiko (1126–1185) of the Imperial House of Japan during theHeian period.
Niinoama is a non-family asteroid of the main belt'sbackground population when applying thehierarchical clustering method to itsproper orbital elements. It orbits the Sun in theouter main-belt at a distance of 3.1–3.2 AU once every 5 years and 7 months (2,044 days). Its orbit has aneccentricity of 0.01 and aninclination of 9° with respect to theecliptic.[1] A firstprecovery was taken atPalomar Observatory in May 1950, extending the body'sobservation arc by more than 41 years prior to its official discovery observation at Yakiimo.[10]
Thisminor planet was named afterTaira no Tokiko (1126–1185), second wife of military leaderTaira no Kiyomori and grandmother ofEmperor Antoku after whom3686 Antoku is named. According to theTale of the Heike, she drowned herself during theBattle of Dan-no-ura together with the boy-Emperor Antoku in her arms.[2][11] Theofficial naming citation was published by theMinor Planet Center on 10 November 1992 (M.P.C. 21132).[12]
Niinoama is an assumedC-type asteroid.[3]
Photometric observations ofNiinoama collected during 2008 show arotation period of4.73±0.01 hours with a brightness variation of 0.32 ± 0.04magnitude (U=3),[9] superseding an early measurement that gave4.725±0.002 hours (U=1+).[13]
According to the surveys carried out by the Infrared Astronomical SatelliteIRAS, the JapaneseAkari satellite, and NASA'sWide-field Infrared Survey Explorer with its subsequentNEOWISE mission,Niinoama measures between 26.50 and 42.51 kilometers in diameter and its surface has analbedo of 0.079.[5][7][8][4] TheCollaborative Asteroid Lightcurve Link adopts a diameter of 27.96 kilometers from IRAS, and derives an albedo of 0.1082 based on anabsolute magnitude of 10.8.[3]
