86 Semele

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.^[4] This object is classified as a C-type asteroid and is probably composed of carbonates.

86 Semele

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/[1]
Named after	Semele
Minor planet category	Main belt
Adjectives	Semelean /sɛmɪˈleɪən/[2]
Orbital characteristics[3]
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°
Argument of perihelion	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[4]
Geometric albedo	0.047 [5]
Spectral type	C
Absolute magnitude (H)	8.54

Semele was discovered by German astronomer Friedrich Tietjen on January 4, 1866.^[6] 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.^[7]