|Discovered by||Annibale de Gasparis|
|Discovery date||November 2, 1850|
|Minor planet category||Main belt|
|Epoch July 14, 2004 (JD 2453200.5)|
|Aphelion||417.953 Gm (2.794 AU)|
|Perihelion||352.719 Gm (2.358 AU)|
|Semi-major axis||385.336 Gm (2.576 AU)|
|Orbital period||1,509.977 d (4.13 a)|
|Average orbital speed||18.56 km/s|
|Longitude of ascending node||43.305°|
|Argument of perihelion||81.401°|
|Dimensions||207.6 ± 8.3 km (IRAS)
|Mean density||3.46±0.79 g/cm³|
|Equatorial surface gravity||~0.0580 m/s²|
|Escape velocity||~0.1098 km/s|
|Rotation period||0.2935 d
|Spectral type||G-type asteroid|
|Apparent magnitude||9.71 to 12.46|
|Absolute magnitude (H)||6.74|
13 Egeria is a large main-belt G-type asteroid. It was discovered by A. de Gasparis on November 2, 1850. Egeria was named by Urbain Le Verrier, whose computations led to the discovery of Neptune, after the mythological nymph Egeria of Aricia, Italy, the wife of Numa Pompilius, second king of Rome.
Egeria occulted a star on January 8, 1992. Its disc was determined to be quite circular (217×196 km). On January 22, 2008, it occulted another star, and this occultation was timed by several observers in New Mexico and Arizona, coordinated by the IOTA Asteroid Occultation Program. The result showed that Egeria presented an approximately circular profile to Earth of 214.8x192 km, well in agreement with the 1992 occultation. It has also been studied by radar.
In 1988 a search for satellites or dust orbiting this asteroid was performed using the UH88 telescope at the Mauna Kea Observatories, but the effort came up empty. Spectral analysis of Egeria shows it to be unusually high in water content, between 10.5-11.5% water by mass. This makes Egeria a prominent candidate for future water-mining ventures.
- "JPL Small-Body Database Browser: 13 Egeria". 2008-11-04 last obs. Retrieved 2008-11-25.
- Jim Baer (2008). "Recent Asteroid Mass Determinations". Personal Website. Retrieved 2008-11-28.
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- apmag 9.71 (2061-Nov-06) to 12.46 (1990-Mar-12) JPL Horizons daily output for 1950 to 2099
- Rivkin, A. S.; J. K. Davies, S. L. Ellison, L. A. Lebofsky. "High-resolution 2.5–3.5 M Observations of C-, B- and G-class asteroids." (PDF). Retrieved 2008-04-20.
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- Gradie, J.; Flynn, L. (March 1988), "A Search for Satellites and Dust Belts Around Asteroids: Negative Results", Abstracts of the Lunar and Planetary Science Conference 19: 405–406, Bibcode:1988LPI....19..405G.
- JPL Ephemeris
- "Elements and Ephemeris for (13) Egeria". Minor Planet Center. (displays Elong from Sun and V mag for 2011)