121 Hermione
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121 Hermione is a very large binary asteroid discovered in 1872. It orbits in the Cybele group in the far outer asteroid belt.<ref name=tanton/> 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.<ref name=tanton>Template:Cite book</ref>
Discovery
Hermione was discovered by J. C. Watson on 12 May 1872 from Ann Arbor, Michigan, in the United States,<ref name=tanton/> and named after Hermione, daughter of Menelaus and Helen in Greek mythology.<ref name="springer" />
Physical properties
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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.<ref name=MarKaaHom06/> 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.<ref name="MarHesDes05" /> 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.<ref name=MarHesDes05/> 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. Template:Infobox planet
Moon
A satellite of Hermione was discovered in 2002 with the Keck II telescope.<ref name=tanton/> It is about 8 miles (13 km) in diameter.<ref name=tanton/> 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.<ref name="Johnston"/><ref name=MarKaaHom06/>
Notes
References
External links
- 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)
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- Template:JPL small body
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