Hilda Family
The Hilda or Hildian asteroids are a dynamical group of asteroids in a 3:2 orbital resonance with Jupiter. 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 passes through all of these three points in sequence. Consequently, a Hilda's orbit has a semi-major axis between 3.7 AU and 4.2 AU, an eccentricity less than 0.3, and an inclination less than 20°. They do not form a true asteroid family, in the sense that they do not descend from a common parent object. The namesake is 153 Hilda, discovered by Johann Palisa in 1875. 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.
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