121 Hermione facts for kids

121 Hermione is a very big asteroid of the dark C spectral type, orbiting in the Cybele group in the farther part of the main belt. As a C-type, it is probably made of carbonate.

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)