Hilda asteroid in the context of Semi-major axis

The Jupiter trojans, commonly called trojan asteroids or simply trojans, are a large group of asteroids that share the planet Jupiter's orbit around the Sun. Relative to Jupiter, each trojan librates around one of Jupiter's stable Lagrange points: either L₄, existing 60° ahead of the planet in its orbit, or L₅, 60° behind. Jupiter trojans are distributed in two elongated, curved regions around these Lagrangian points with an average semi-major axis of about 5.2 AU.

The first Jupiter trojan discovered, 588 Achilles, was spotted in 1906 by German astronomer Max Wolf. More than 15,300 Jupiter trojans have been found as of October 2025. By convention, they are each named from Greek mythology after a figure of the Trojan War, hence the name "trojan". The total number of Jupiter trojans larger than 1 km in diameter is believed to be about 1 million, approximately equal to the number of asteroids larger than 1 km in the asteroid belt. Like main-belt asteroids, Jupiter trojans form families.

The Hilda family (001) is an ancient collisional asteroid family of at least 409 known asteroids, named for its largest member, the 170-kilometre (110 mi)-across asteroid 153 Hilda. It lies within the larger dynamical group of Hilda asteroids, a group of asteroids in the 3:2 orbital resonance with Jupiter. All members of the family are dark P-type asteroids with albedos of around 0.06. Another asteroid family in the Hilda dynamical group is the Schubart family, named for its largest member, 1911 Schubart.

An asteroid family is a group of physically related asteroids usually created by a collision with an original larger asteroid, with the fragments continuing on similar orbits to the original. This is distinct from a dynamical group in that the members of a dynamical group only share similar orbits because of gravitational interactions with planets, which concentrate asteroids in a particular orbital range. Members of the Hilda family are both part of the wider Hilda dynamical group, and fragments of 153 Hilda. The family is considered a non-catastrophic asteroid family because 153 Hilda, its largest member, makes up nearly 3/4 of the family's total mass, rather than simply being the largest of a number of fragments each making up a small fraction of the original destroyed asteroid.

The Schubart family (002) is a collisional asteroid family of at least 353 known asteroids, named for its largest member, the 67-kilometre (42 mi)-across asteroid 1911 Schubart. It lies within the larger dynamical group of Hilda asteroids, a group of asteroids in the 3:2 orbital resonance with Jupiter. Like its namesake, it's named after the largest member, 1911 Schubart. All members of the family are dark P-type asteroids with albedos of around 0.04. Another asteroid family in the Hilda dynamical group is the Hilda family, named for its largest member, 153 Hilda.

An asteroid family is a group of physically related asteroids usually created by a collision with an original larger asteroid, with the fragments continuing on similar orbits to the original. This is distinct from a dynamical group in that the members of a dynamical group only share similar orbits because of gravitational interactions with planets, which concentrate asteroids in a particular orbital range. Members of the Schubart family are both part of the wider Hilda dynamical group, and fragments of a single original asteroid. The family is considered a catastrophic asteroid family because even its largest member, 1911 Schubart, does not make up a majority of the family's mass.

A Kirkwood gap is a gap or dip in the distribution of the semi-major axes (or equivalently of the orbital periods) of the orbits of main-belt asteroids. They correspond to the locations of orbital resonances with Jupiter. The gaps were first noticed in 1866 by Daniel Kirkwood, who also correctly explained their origin in the orbital resonances with Jupiter while a professor at Jefferson College in Canonsburg, Pennsylvania.

For example, there are very few asteroids with semimajor axis near 2.50 AU, period 3.95 years, which would make three orbits for each orbit of Jupiter (hence, called the 3:1 orbital resonance). Other orbital resonances correspond to orbital periods whose lengths are simple fractions of Jupiter's. The weaker resonances lead only to a depletion of asteroids, while spikes in the histogram are often due to the presence of a prominent asteroid family (see List of asteroid families).