The Eunomia or Eunomian family () is a large asteroid family of S-type asteroids named after the asteroid 15 Eunomia. It is the most prominent family in the intermediate asteroid belt and the 6th-largest family with nearly six thousand known members, or approximately 1.4% of all asteroids in the asteroid belt. It is likely that the parent body was at least partly differentiated, because the surface of Eunomia and spectra of the smaller family members show some variation. This notwithstanding, other studies have indicated that the body that was definitively shattered by the impact that created the family was probably already somewhat fragmented by previous smaller collisions. The impactor was probably a smaller, yet still very substantial asteroid of 50 km diameter (or so) that hit at a speed of about 22,000 km/h.
The other Eunomian asteroids are quite regularly distributed in orbital space around Eunomia. The next largest member identified by the analysis was 258 Tyche of 65 km diameter. However, its orbit lies at the very margin of what can be considered the family region, and it may well be an interloper. The largest clear family members are about 30 km diameter, with several asteroids in this size range.
Spectroscopic studies have shown that the family members span a noticeable range of compositions, although all remain within the S spectral class. As such they are of generally stony (rather than icy) surface composition that includes silicates and some nickel-iron, and are quite bright for their size.
The family contains relatively large numbers of small objects. Since most of these smaller objects are "eroded" away over time due to secondary collisions, gravitational perturbations, and the Yarkovsky effect, this indicates that the Eunomia family was created relatively recently (on an astronomical timescale).
The Cassini-Huygens spacecraft flew by 2685 Masursky, a small family member, in 2000. However, the encounter distance
of about one million kilometers was too large for surface features to be resolved.
Location and size
The Eunomia family is located between the 3:1 and 8:3 resonances with Jupiter, at relatively high inclinations.
A HCM numerical analysis by Zappalà, et al. for 96944 minor planets in 2005 yielded 4649 objects lying within the rectangular-shaped region defined by the first table above. By 2014, Nesvorný identified at total of 5,670, or approximately 1.4% of all asteroids, using the Hierarchical Clustering Method.
</references> <!-- end of reflist -->