121 Hermione
.png) A three-dimensional model of 121 Hermione based on its light curve. | |||||||||||||
| Discovery[1] | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Discovered by | James Craig Watson | ||||||||||||
| Discovery date | 1872-05-12 | ||||||||||||
| Designations | |||||||||||||
| MPC designation | (121) Hermione | ||||||||||||
| Pronunciation | /hɜːrˈmaɪ.əni/ hur-MY-ə-nee | ||||||||||||
Named after | Hermione | ||||||||||||
| 1970 VE | |||||||||||||
Main belt  (Cybele) | |||||||||||||
| Orbital characteristics[2] | |||||||||||||
| Epoch December 31, 2006 (JD 2454100.5) | |||||||||||||
| Aphelion | 588.328 Gm (3.933 AU) | ||||||||||||
| Perihelion | 446.029 Gm (2.982 AU) | ||||||||||||
| 517.179 Gm (3.457 AU) | |||||||||||||
| Eccentricity | 0.138 | ||||||||||||
| 2347.854 d (6.43 a) | |||||||||||||
Average orbital speed | 15.94 km/s | ||||||||||||
| 248.068° | |||||||||||||
| Inclination | 7.604° | ||||||||||||
| 73.209° | |||||||||||||
| 296.215° | |||||||||||||
| Known satellites | S/2002 (121) 1 | ||||||||||||
| Physical characteristics | |||||||||||||
| Dimensions |
268×186×183 km[3] 254±4 × 125±9 km[4] | ||||||||||||
Mean radius | 95 km[4] | ||||||||||||
| Mass |
5.38 ± 0.3 ×1018 kg[3] 5.4 ± 0.3×1018 kg[5] | ||||||||||||
Mean density |
1.13 ± 0.3 g/cm³[3] 1.8 ± 0.2 g/cm³[5][6] | ||||||||||||
Equatorial surface gravity | 0.022 m/s²[7] | ||||||||||||
Equatorial escape velocity | 0.075 km/s[7] | ||||||||||||
Sidereal rotation period | 0.2313 d (5.551 h)[8] | ||||||||||||
| 73° | |||||||||||||
Pole ecliptic latitude | +10 ± 2°[5] | ||||||||||||
Pole ecliptic longitude | 1.5 ± 2° | ||||||||||||
| 0.0482 ± 0.002[9] | |||||||||||||
| |||||||||||||
| C [10] | |||||||||||||
| 7.31[9] | |||||||||||||
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121 Hermione is a very large asteroid discovered in 1872. It orbits in the Cybele group[11] in the far outer asteroid belt. As an asteroid of the dark C spectral type, it is probably composed of carbonaceous materials. In 2002, a small moon was found to be orbiting Hermione.[11]
Hermione is a Cybele asteroid and orbits beyond most of the main-belt asteroids.
Discovery[edit]
Hermione was discovered by J. C. Watson on May 12, 1872, from Ann Arbor,[11] and named after Hermione, daughter of Menelaus and Helen in Greek mythology.
Physical properties[edit]
The asteroid has a bi-lobed shape, as evidenced by adaptive optics images, the first of which were taken in December 2003 with the Keck telescope.[4] Of several proposed shape models that agreed with the images, a "snowman"-like shape was found to best fit the observed precession rate of Hermione's satellite.[5] In this "snowman" model, the asteroid's shape can be approximated by two partially overlapping spheres of radii 80 and 60 km, whose centers are separated by a distance of 115 km. A simple ellipsoid shape was ruled out.
Observation of the satellite's orbit has made possible an accurate determination of Hermione's mass.[5] For the best-fit "snowman" model, the density is found to be 1.8 ± 0.2 g/cm³, giving a porosity on the order of 20%, and possibly indicating that the main components are fractured solid bodies, rather than the asteroid being a rubble pile.
Occultations by Hermione have been successfully observed three times so far, the last time in February 2004.
| Discovery[12] | |
|---|---|
| Discovered by |
W. J. Merline, P. M. Tamblyn, C. Dumas, L. M. Close, C. R. Chapman, F. Menard, W. M. Owen, and D. C. Slater |
| Discovery date | 2002-09-28 |
| Designations | |
| LaFayette | |
|
Main belt (Cybele) | |
| Orbital characteristics[13] | |
| 768 ± 11 km | |
| Eccentricity | 0.001 ± 0.001 |
| 2.582 ± 0.002 d | |
Average orbital speed | 22 m/s |
| Inclination |
3 ± 2° with respect to Hermione pole |
| Satellite of | 121 Hermione |
| Physical characteristics | |
| Dimensions | 12 ± 4 km[4] |
| Mass | ~1.6×1015 kg[14] |
Equatorial escape velocity | ~ 6 m/s |
| 13.0[4] | |
|
| |
Moon[edit]
A satellite of Hermione was discovered in 2002 with the Keck II telescope.[11] It is about 8 miles (13 km) in diameter.[11] The satellite is provisionally 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.[citation needed]
References[edit]
- ^ Discovery Circumstances: Numbered Minor Planets, Minor Planet Centre
- ^ ASTORB orbital elements database, Lowell Observatory
- ^ a b c Jim Baer (2008). "Recent Asteroid Mass Determinations". Personal Website. Retrieved 2008-12-07.
- ^ a b c d e F. Marchis; et al. (2006). "Shape, size and multiplicity of main-belt asteroids I. Keck Adaptive Optics survey". Icarus. 185 (1): 39–63. Bibcode:2006Icar..185...39M. doi:10.1016/j.icarus.2006.06.001. PMC 2600456
. PMID 19081813.
- ^ a b c d e F. Marchis; et al. (2005). "Mass and density of Asteroid 121 Hermione from an analysis of its companion orbit". Icarus. 178 (2): 450. Bibcode:2005Icar..178..450M. doi:10.1016/j.icarus.2005.05.003.
- ^ Using the "snowman" shape model, which best matches the value of J2 implied from precession.
- ^ a b On the extremities of the long axis.
- ^ IAUC 8264
- ^ a b Supplemental IRAS minor planet survey Archived 2010-01-17 at WebCite
- ^ PDS node taxonomy database Archived 2010-01-17 at WebCite
- ^ a b c d e Linda T. Elkins-Tanton - Asteroids, Meteorites, and Comets (2010) - Page 96 (Google Books)
- ^ IAUC 7980 Archived 2006-05-01 at the Wayback Machine.
- ^ 121 Hermione and S/2002 (121) 1, orbit data website maintained by F. Marchis.
- ^ Assuming a similar density to the primary.
External links[edit]
- 121 Hermione and S/2002 (121) 1, orbit data website maintained by F. Marchis. Includes adaptive optics images, orbit diagrams, and shape models.
- (121) Hermione, datasheet, johnstonsarchive.net
- Asteroids with Satellites, Robert Johnston, johnstonsarchive.net
- Tally of Asteroids Harboring Moons Grows Beyond 30 (Space.com, 3 October 2002)
- 121 Hermione at AstDyS-2, Asteroids—Dynamic Site
- 121 Hermione at the JPL Small-Body Database
