65 Cybele

65 Cybele

3D shape model of Cybele from ground-based observations.
Discovery
Discovered by	Ernst Wilhelm Tempel
Discovery date	March 8, 1861
Designations
Pronunciation	/ˈsɪbᵻliː/ SIB-əl-ee
Named after	Cybele
Alternative names
Minor planet category	outer main belt (Cybele)
Orbital characteristics
Epoch December 31, 2006 (JD 2454100.5)
Aphelion	567.544 Gm (3.794 AU)
Perihelion	459.654 Gm (3.073 AU)
Semi-major axis	513.599 Gm (3.433 AU)
Eccentricity	0.105
Orbital period	2323.521 d (6.36 a)
Average orbital speed	16.03 km/s
Mean anomaly	279.683°
Inclination	3.548°
Longitude of ascending node	155.808°
Argument of perihelion	105.757°
Physical characteristics
Dimensions	302×290×232 km 273.0±11.9 km 237.3 km IRAS
Mass	1.78×1019 kg
Mean density	0.99±0.20 g/cm³
Surface gravity	0.0663 m/s²
Escape velocity	0.1255 km/s
Rotation period	4.041 h
Albedo	0.050 ± 0.005 0.071
Temperature	~150 K
Spectral type	Xc/P
Apparent magnitude	10.67 to 13.64
Absolute magnitude (H)	6.62

65 Cybele is one of the largest asteroids in the Solar System and is located in the outer asteroid belt. It gives its name to the Cybele family of asteroids that orbit outward from the Sun from the 2:1 orbital resonance with Jupiter. Cybele is a X-type asteroid, meaning that it is dark in color and carbonaceous in composition. It was discovered in 1861 by Ernst Tempel and named after Cybele, the earth goddess.

Discovery and naming

Cybele was discovered on March 8, 1861, by Ernst Tempel from the Marseilles Observatory. A minor controversy arose from its naming process. Tempel had awarded the honour of naming the asteroid to Carl August von Steinheil in recognition of his achievements in telescope production. Von Steinheil elected to name it "Maximiliana" after the reigning monarch Maximilian II of Bavaria. At the time, asteroids were conventionally given classical names, and a number of astronomers protested this contemporary appellation. The name Cybele was chosen instead, referring to the Phrygian goddess of the earth.

Physical characteristics

The first Cybelian stellar occultation was observed on October 17, 1979 in the Soviet Union. The asteroid appeared to have an irregular shape, with the longest chord being measured as 245 km, closely matching the diameter of 237 km determined by the IRAS satellite in 1983. During the same 1979 occultation, a hint of a possible 11 km wide satellite was detected.

The diameter from IRAS observations in 1983 is 237±4 km. In 1985, Green estimated Cybele to have a diameter of 330 km. In 2004, Müller estimated Cybele using thermophysical modelling (TPM) to have dimensions of 302×290×232 km.

In 2007, David Weintraub suggested that it might be in hydrostatic equilibrium, but it this is no longer considered a possibility.

Spectrum

Examination of the asteroid's infrared spectrum shows an absorption feature that is similar to the spectrum of 24 Themis. This can be explained by the presence of water ice. The asteroid may be covered in a layer of fine silicate dust mixed with small amounts of water-ice and organic solids.

Recent occultations

On August 24, 2008, Cybele occulted 2UCAC 24389317, a 12.7-magnitude star in the constellation Ophiuchus which showed a long axis of at least 294 km. On October 11, 2009, Cybele occulted a 13.4-magnitude star in the constellation Aquarius.

External links

• Orbital simulation from JPL (Java) / Ephemeris