121 HERMIONE

'121 Hermione' is a very large asteroid of the dark C spectral type, orbiting in the Cybele group in the far outer main belt. As a C-type, it is probably composed of carbonaceous materials. Hermione 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. 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 . 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 . 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 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 . For the best-fit "snowman" model, the density is found to be 1.8 ± 0.2 g/cm³, giving a porosity of the order of 20%, and possibly indicating that the main components are fractured solid bodies, but that the asteroid is rather not a rubble pile. Occultations by Hermione have been successfully observed three times so far, the last time in February, 2004. Contents Satellite (S/2002 (121) 1) References External links Satellite (S/2002 (121) 1)

A satellite of Hermione was discovered in 2002 with the Keck II telescope. 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.

References

1. IAUC 7980
2. Assuming a similar density to the primary.
3. Discovery Circumstances: Numbered Minor Planets, Minor Planet Centre
4. [ftp://ftp.lowell.edu/pub/elgb/astorb.html ASTORB] orbital elements database, Lowell Observatory

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.

★ Data on (121) Hermione from Johnston's archive (maintained by W. R. Johnston)

★ ''Tally of Asteroids Harboring Moons Grows Beyond 30'' (Space.com, 3 October, 2002)