13 Egeria
Egeria (minor planet designation: 13 Egeria) is a large main-belt G-type asteroid. It was discovered by Annibale 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.
| Discovery | |
|---|---|
| Discovered by | Annibale de Gasparis |
| Discovery site | Naples Obs. |
| Discovery date | 2 November 1850 |
| Designations | |
MPC designation | (13) Egeria |
| Pronunciation | /ɪˈdʒɪəriə/ |
Named after | Egeria |
Minor planet category | Main belt |
| Adjectives | Egerian |
| Symbol | (historical) |
| Orbital characteristics | |
| Epoch 13 January 2016 (JD 2457400.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 60342 days (165.21 yr) |
| Aphelion | 2.7927 AU (417.78 Gm) |
| Perihelion | 2.36115 AU (353.223 Gm) |
Semi-major axis | 2.57690 AU (385.499 Gm) |
| Eccentricity | 0.083726 |
Orbital period (sidereal) | 4.14 yr (1510.9 d) |
Average orbital speed | 18.56 km/s |
Mean anomaly | 261.863° |
Mean motion | 0° 14m 17.736s / day |
| Inclination | 16.539° |
Longitude of ascending node | 43.239° |
| 80.294° | |
| Earth MOID | 1.43999 AU (215.419 Gm) |
| Jupiter MOID | 2.35966 AU (353.000 Gm) |
| TJupiter | 3.364 |
| Physical characteristics | |
| Dimensions | c/a = 0.76±0.06 214.8×192 |
Mean diameter | 202±3 km 207.6 ± 8.3 km (IRAS) |
Mean radius | 103.82 ± 4.15 km |
| Mass | (9.2±2.1)×1018 kg (15.9±4.4)×1018 kg |
Mean density | 2.13±0.49 g/cm3 3.4±1.0 g/cm3 |
Equatorial surface gravity | ≈0.0580 m/s2 |
Equatorial escape velocity | ≈0.1098 km/s |
Synodic rotation period | 0.2935 d (7.045 h) |
| 0.087 0.0825 ± 0.007 | |
| Temperature | ~174 K |
| G-type asteroid | |
| 9.71 to 12.46 | |
| 6.74 | |
The historical symbol for Egeria was a buckler. It is in the pipeline for Unicode 17.0 as U+1CEC6 ().
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 214.8×192 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, 10.5–11.5% water by mass. This makes Egeria a prominent candidate for future water-mining ventures.