121 Hermione
Hermione (minor planet designation: 121 Hermione) is a very large binary asteroid discovered in 1872. It orbits in the Cybele group in the far outer asteroid belt. As an asteroid of the dark C spectral type, it is probably composed of carbonaceous materials. In 2002, a small moon was found to be orbiting Hermione.
121 Hermione and its moon | |
| Discovery | |
|---|---|
| Discovered by | James Craig Watson |
| Discovery date | 12 May 1872 |
| Designations | |
MPC designation | (121) Hermione |
| Pronunciation | /hɜːrˈmaɪ.əniː/ |
Named after | Hermione (Greek mythology) |
Alternative designations | A872 JA; 1970 VE |
Minor planet category | main-belt · Cybele |
| Adjectives | Hermionean /hɜːrmaɪ.əˈniːən/ |
| Orbital characteristics | |
| Epoch 23 March 2018 (JD 2458200.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 145.96 yr (53,312 d) |
| Aphelion | 3.9067 AU |
| Perihelion | 2.9889 AU |
Semi-major axis | 3.4478 AU |
| Eccentricity | 0.1331 |
Orbital period (sidereal) | 6.40 yr (2,338 d) |
Mean anomaly | 157.08° |
Mean motion | 0° 9m 14.4s / day |
| Inclination | 7.5975° |
Longitude of ascending node | 73.127° |
| 298.18° | |
| Known satellites | S/2002 (121) 1 |
| Physical characteristics | |
| Dimensions | 268 × 186 × 183 km (254 ± 4) × (125 ± 9) km |
Mean radius | 95 km |
| Volume | (3.0±0.4)×106 km3 |
| Mass | (5.381±5%)×1018 kg |
Mean density | 1.8 ± 0.2 g/cm3 |
Equatorial surface gravity | 0.022 m/s2 |
Equatorial escape velocity | 0.075 km/s |
Sidereal rotation period | 0.2313 d (5.551 h) |
| 73° | |
Pole ecliptic latitude | +10 ± 2° |
Pole ecliptic longitude | 1.5 ± 2° |
| 0.0482 ± 0.002 | |
| C | |
| 7.31 | |
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