Hilda group

normal and narrowed arteries

(Left) The Hildas Triangle against a background of all known asteroids up to Jupiter's orbit. (Right) The positions of the Hildas against a background of their orbits.

The Hilda group is a group of asteroids that define the outer edge of the main asteroid belt, about 4 astronomical units from the Sun. These asteroids have become locked into their present orbits by a gravitational resonance with Jupiter: a Hilda makes exactly three orbits of the Sun for every two that Jupiter makes.


The Hildas taken together constitute a dynamic triangular figure with slightly convex sides and trimmed apices in the triangular libration points of Jupiter—the "Hildas Triangle".


The prototype is 153 Hilda, discovered in 1875 by Johanna Palisa.


Data for 153 Hilda
diameter 171 km
spectral class P
semimajor axis 3.975 AU
perihelion 3.408 AU
aphelion 4.543 AU
eccentricity 0.143
inclination 7.84°
period 9.72 years