86 Semele
Semele (minor planet designation: 86 Semele) is a large and very dark main-belt asteroid with an orbital period of 5.5 years. It is rotating with a period of 16.6 hours, and varies in magnitude by 0.13 during each cycle. This object is classified as a C-type asteroid and is probably composed of carbonates.
Orbit of 86 Semele on 1 Jan 2009 | |
| Discovery | |
|---|---|
| Discovered by | Friedrich Tietjen |
| Discovery date | January 4, 1866 |
| Designations | |
MPC designation | (86) Semele |
| Pronunciation | /ˈsɛmɪlə/ |
Named after | Semele |
Minor planet category | Main belt |
| Adjectives | Semelean /sɛmɪˈleɪən/ |
| Orbital characteristics | |
| Epoch December 31, 2006 (JD 2454100.5) | |
| Aphelion | 562.652 Gm (3.761 AU) |
| Perihelion | 369.116 Gm (2.467 AU) |
Semi-major axis | 465.884 Gm (3.114 AU) |
| Eccentricity | 0.208 |
Orbital period (sidereal) | 2,007.366 d (5.50 a) |
Average orbital speed | 16.69 km/s |
Mean anomaly | 264.875° |
| Inclination | 4.822° |
Longitude of ascending node | 86.452° |
| 307.886° | |
| Physical characteristics | |
| Dimensions | 120.6 km |
| Mass | 1.8×1018 kg |
Equatorial surface gravity | 0.0337 m/s² |
Equatorial escape velocity | 0.0638 km/s |
Synodic rotation period | 16.641±0.001 h |
| 0.047 | |
| C | |
| 8.54 | |
Semele was discovered by German astronomer Friedrich Tietjen on January 4, 1866. It was his first and only asteroid discovery. It is named after Semele, the mother of Dionysus in Greek mythology.
The orbit of 86 Semele places it in a 13:6 mean motion resonance with the planet Jupiter. The computed Lyapunov time for this asteroid is only 6,000 years, indicating that it occupies a chaotic orbit that will change randomly over time because of gravitational perturbations of the planets. This Lyapunov time is the second lowest among the first 100 named minor planets.