Hermione was found 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 an odd shape, as evidenced by adaptive optics images, the first of which were taken in December 2003, with the Keck telescope. Of many proposed shape models that agreed with the images, a "snowman"-like shape was found to best fit the seen precession rate of Hermione's moon.
Observation of the moon's orbit has made possible a correct determination of Hermione's mass. For the best-fit "snowman" model, the density is found to be 1.8 ± 0.2 g/cm³. This gives a porosity of the order of 20%. This could be because the main asteroids are fractured solid bodies, but not a rubble pile (an asteroid that has been broken up by a collision and pulled back together by gravity).
Occultations by Hermione have been successfully seen three times so far, the last time in February 2004.
Moon (S/2002 (121) 1)[change | change source]
References[change | change source]
- F. Marchis; et al. (2006). "Shape, size and multiplicity of main-belt asteroids I. Keck Adaptive Optics survey". Icarus. 185: 39.
- F. Marchis; et al. (2005). "Mass and density of Asteroid 121 Hermione from an analysis of its companion orbit". Icarus. 178: 450.
- IAUC 7980[dead link]
- 121 Hermione and S/2002 (121) 1, orbit data website maintained by F. Marchis.
- Assuming a similar density to the primary.
- Discovery Circumstances: Numbered Minor Planets, Minor Planet Centre Archived 20 June 2007 at WebCite
- ASTORB orbital elements database, Lowell Observatory
- Using the "snowman" shape model, which best matches the value of J2 implied from precession.
- On the extremities of the long axis.
- IAUC 8264[dead link]
- Supplemental IRAS minor planet survey Archived 17 January 2010 at WebCite
- PDS node taxonomy database Archived 16 January 2010 at WebCite
Other websites[change | change source]
- 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)