| Minorplanet: | yes |
| 4959 Niinoama | |
| Background: |
|
| Discovery Ref: |   |
| Discovered: | 15 August 1991 |
| Mpc Name: | (4959) Niinoama |
| Alt Names: | 1958 TZ 1966 CB1968 MC 1972 EB 1984 OO1985 OD |
| Named After: | Taira no Tokiko |
| Orbit Ref: |   |
| Epoch: | 4 September 2017 (JD 2458000.5) |
| Uncertainty: | 0 |
| Observation Arc: | 67.15 yr (24,528 days) |
| Perihelion: | 3.1272 AU |
| Semimajor: | 3.1516 AU |
| Eccentricity: | 0.0077 |
| Period: | 5.59 yr (2,044 days) |
| Mean Motion: | / day |
| Inclination: | 8.9913° |
| Asc Node: | 128.79° |
| Arg Peri: | 320.53° |
| Mean Diameter: | km km km km |
| Albedo: | 0.1081 |
| Abs Magnitude: | 10.810.9 |
4959 Niinoama (prov. designation:) is a dark background asteroid from the outer regions of the asteroid belt. It was discovered by Japanese astronomers Akira Natori and Takeshi Urata at JCPM Yakiimo Station on 15 August 1991. The presumed carbonaceous C-type asteroid has a rotation period of 4.7 hours and measures approximately 36km (22miles) in diameter. It was named after Taira no Tokiko (1126–1185) of the Imperial House of Japan during the Heian period.
Niinoama is a non-family asteroid of the main belt's background population when applying the hierarchical clustering method to its proper orbital elements. It orbits the Sun in the outer main-belt at a distance of 3.1–3.2 AU once every 5 years and 7 months (2,044 days). Its orbit has an eccentricity of 0.01 and an inclination of 9° with respect to the ecliptic. A first precovery was taken at Palomar Observatory in May 1950, extending the body's observation arc by more than 41 years prior to its official discovery observation at Yakiimo.
This minor planet was named after Taira no Tokiko (1126–1185), second wife of military leader Taira no Kiyomori and grandmother of Emperor Antoku after whom is named. According to the Tale of the Heike, she drowned herself during the Battle of Dan-no-ura together with the boy-Emperor Antoku in her arms.[1] The was published by the Minor Planet Center on 10 November 1992 .
Niinoama is an assumed C-type asteroid.
Photometric observations of Niinoama collected during 2008 show a rotation period of hours with a brightness variation of 0.32 ± 0.04 magnitude, superseding an early measurement that gave hours .
According to the surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite, and NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Niinoama measures between 26.50 and 42.51 kilometers in diameter and its surface has an albedo of 0.079. The Collaborative Asteroid Lightcurve Link adopts a diameter of 27.96 kilometers from IRAS, and derives an albedo of 0.1082 based on an absolute magnitude of 10.8.