91 Aegina

91 Aegina (from Latin Aegīna, Aegīnēta)^[4] is a large main-belt asteroid. It was discovered by French astronomer Édouard Jean-Marie Stephan on 4 November 1866. It was his second and final asteroid discovery. The first was 89 Julia. The asteroid's name comes from Aegina, a Greek mythological figure associated with the island of the same name.

91 Aegina

Orbital diagram
Discovery
Discovered by	Édouard Stephan
Discovery date	4 November 1866
Designations
MPC designation	(91) Aegina
Pronunciation	/ɪˈdʒaɪnə/[1]
Named after	Aegina
Minor planet category	Main belt
Adjectives	Aeginetan /iːdʒɪˈniːtən/[2]
Orbital characteristics
Epoch 31 December 2006 (JD 2454100.5)
Aphelion	428.453 Gm (2.864 AU)
Perihelion	346.826 Gm (2.318 AU)
Semi-major axis	387.640 Gm (2.591 AU)
Eccentricity	0.105
Orbital period (sidereal)	1,523.536 d (4.171 yr)
Average orbital speed	18.45 km/s
Mean anomaly	183.458°
Inclination	2.109°
Longitude of ascending node	10.806°
Argument of perihelion	73.371°
Physical characteristics
Dimensions	109.8 km
Mass	1.4×1018 kg
Equatorial surface gravity	0.0307 m/s²
Equatorial escape velocity	0.0580 km/s
Synodic rotation period	6.03 hours
Geometric albedo	0.043 [3]
Spectral type	C
Absolute magnitude (H)	8.84

This body is orbiting the Sun with a period of 4.17 years and an eccentricity of 0.105. The orbit of this object brings it to within 4.9 Gm of the dwarf planet Ceres, and the resulting gravitational interaction has been used to produce mass estimates of the latter.^[5] The cross-section size of the asteroid is 110 km and it has a rotation period of six hours. The surface coloring of 91 Aegina is very dark and this C-type asteroid has probably a primitive carbonaceous composition. Observation of absorption bands at wavelengths of 0.7 and 3μm indicate the presence of hydrated minerals and/or ice grains on the surface.^[6]