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Hilda family


The Hilda or Hildian asteroids are a dynamical group of asteroids in a 3:2 orbital resonance with Jupiter. The namesake is the asteroid 153 Hilda. Hildas move in their elliptical orbits so that their aphelia put them opposite Jupiter, or 60 degrees ahead of or behind Jupiter at the L4 and L5 Lagrangian points. Over three successive orbits each Hilda asteroid approaches all of these three points in sequence. A Hilda's orbit has a semi-major axis between 3.7 AU and 4.2 AU (the average over a long time span is 3.97), an eccentricity less than 0.3, and an inclination less than 20°. Two collisional families exist within the Hilda group: the Hilda family and the Schubart family. The namesake for the latter family is 1911 Schubart. There are more than 1,100 known Hilda asteroids including unnumbered objects.

Hildas' surface colors often correspond to the low-albedo D-type and P-type; however, a small portion are C-type. D-type and P-type asteroids have surface colors, and thus also surface mineralogies, similar to those of cometary nuclei. This implies that they share a common origin.

The asteroids of the Hilda group (Hildas) are in 3:2 mean-motion resonance with Jupiter. That is, their orbital periods are 2/3 that of Jupiter. They move along the orbits with a semimajor axis near 4.0 AU and moderate values of eccentricity (up to 0.3) and inclination (up to 20°). Unlike the Jupiter trojans they may have any difference in longitude with Jupiter, nevertheless avoiding dangerous approaches to the planet.


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