121 Hermione
Encyclopedia : 1 : 12 : 121 : 121 Hermione
| Orbital characteristics [1] | |
|---|---|
| Orbit type | Main belt (Cybele) |
| Semimajor axis | 3.439 AU |
| Perihelion distance | 2.941 AU |
| Aphelion distance | 3.937 AU |
| Orbital period | 6.38 years |
| Inclination | 7.58° |
| Eccentricity | 0.145 |
| Physical characteristics [1] | |
| Diameter | 209 km |
| Mass | 9.3 × 1018 kg |
| Density | 1.8 g/cm³ |
| Rotation period | 9.238 hours |
| Spectral class | C |
| Abs. magnitude | 7.31 |
| Albedo [4] | 0.048 |
| History [2] | |
| Discoverer | J. C. Watson, 1872 |
| Satellites | |
| Designation | S/2002 (121) 1 |
121 Hermione is a very large and dark main belt asteroid. It is probably composed of carbonaceous materials.
It was discovered by J. C. Watson on May 12, 1872, and named after Hermione, daughter of Menelaus and Helen in Greek mythology.
Hermione is a Cybele asteroid and orbits beyond most of the main belt asteroids.
A satellite of Hermione was discovered in 2002 from the Keck II telescope. The satellite measures about 18 km in diameter and orbits at a distance of about 800 km. One revolution around the primary takes 1.63 days to complete. The satellite is currently designated S/2002 (121) 1. It has not yet been officially named, but "LaFayette" has been proposed by a group of astronomers in reference to the frigate used in secret by the Marquis de Lafayette to reach America to help the insurgents.
In December 2003, the adaptive optics of the Keck telescope were able to resolve the shape of Hermione. The bi-lobated shape of Hermione is easily perceived from the images.
The satellite discovery made possible an accurate measurement of mass and density of the asteroid. Early results indicate a very porous body, but further studies have cast doubt on this.
Occultations by Hermione have been successfully observed three times so far, the last time in February, 2004.
External links
- [Data from Johnston's Archive]
- [Space.com: Tally of Asteroids Harboring Moons Grows Beyond 30]
- [121 Planetary Society: Hermione has a Companion]
- [Bi-lobated Shape of 121 Hermione]
- [Orbit of "LaFayette" (Hermione's companion)]
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