Jupiter has a lot of asteroids accompanying it in its orbit. The most famous, and most numerous, of these are the Trojan asteroids, swarms of thousands of asteroids orbiting in Jupiter's L4 and L5 points. The Hilda family of asteroids are an orbiting ring of 1,000+ asteroids that orbit slightly inside of Jupiter's orbit.

These asteroids are in a 3:2 orbital resonance with Jupiter; the largest asteroid, 153 Hilda, takes 7.9 years to orbit the sun, while Jupiter takes 11.9 years. The orbits of these asteroids generally lie just inside of Jupiter's orbit. They pass regularly by Jupiter, past Jupiter's L4 point, and slowly around until they pass Jupiter's L5 point. Despite the gravitational forces acting on them as they pass by Jupiter and the clouds of asteroids swarming the Lagrangian points, the Hildas are fairly stable in their orbits -- the effects of instabilities are estimated over the course of billions of years.

In the early 1980s Joachim Schubart noted that there appeared to be at least two distinct groups of Hilda asteroids, as determined through looking at their current orbits and groupings and working back to attempt to determine their collisional histories. The groups are named after the first, and largest, asteroid discovered in each group, giving us the Hilda family and the Schubart family (as Wikipedia had erroneously named this the 'Scubart' family, either spelling is now fairly common on the internet). Both groups follow approximately the same elliptical orbits, and to avoid confusion, you may see the asteroids as a group referred to as the 'J 3/2 population' (3/2 referring to the orbital resonance they all share). There are a number of additional asteroids that follow this orbit that do not appear to belong to either family.

We are talking about fairly large asteroids here. 1911 Schubart has a diameter of 80 km, while 153 Hilda has a hefty diameter of 170 km. As of 1993 there were 1267 asteroids identified within the J 3/2 population, and there are certainly many that we have not observed yet, although they will be smaller, less impressive asteroids. These asteroids are quite widely spread out, with the asteroidal stream being 1 AU to 1.4 AU in width.

Unlike the Trojans, the Hildas have not given their name to other groups of analogous asteroids; the only other planet in out solar system with identified asteroids in 3/2 resonance is Neptune, which has its attendant plutinos.

Further reading: Asteroid families in the first order resonances with Jupiter (.pdf)

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