Eunomia family
The Eunomia or Eunomian family (Template:Small) 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.<ref name="Ferret" /><ref name="Nesvorny-2014" />Template:Rp
Characteristics
By far the largest member is 15 Eunomia, the largest of all the "stony" S-type asteroid, It is about 300 km across along its longest axis, has a 250 km mean radius, and lies close to the barycenter of the family. Eunomia has been estimated to contain about 70–75% of the matter from the original parent body. This had a mean diameter of about 280 km and was disrupted by the catastrophic impact that created the family.<ref name="Tanga 1999">Template:Cite journalTemplate:Dead linkTemplate:Cbignore</ref> 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.<ref name="Reed 1997">Template:Cite journalTemplate:Dead linkTemplate:Cbignore</ref><ref name="Lazzaro 1999">Template:Cite journal</ref><ref name="Nathues 2005">Template:Cite journalTemplate:Dead linkTemplate:Cbignore</ref> 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.<ref name="Michel 2004">Template:Cite journalTemplate:Dead linkTemplate:Cbignore</ref> 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.<ref name="Michel 2001">Template:Cite journal</ref>
The other Eunomian asteroids are quite regularly distributed in orbital space around Eunomia. The next largest member identified by the<ref name="Zappala 1995">Template:Cite journal</ref> 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).<ref name="Michel 2001" /><ref name="Michel 2002">Template:Cite journalTemplate:Dead linkTemplate:Cbignore</ref>
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.<ref name="Zappala 1995"/> determined a large group of 'core' family members, whose proper orbital elements lie in the approximate ranges
| ap | ep | ip | |
|---|---|---|---|
| min | 2.54 AU | 0.121 | 11.6° |
| max | 2.72 AU | 0.180 | 14.8° |
At the present epoch, the range of osculating orbital elements of these core members is
| a | e | i | |
|---|---|---|---|
| min | 2.53 AU | 0.078 | 11.1° |
| max | 2.72 AU | 0.218 | 15.8° |
The Zappalà 1995 analysis found 439 core members, while a search of a recent proper element database<ref name="AstDys">Template:Cite web</ref> 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.<ref name="Ferret" /><ref name="Nesvorny-2014" />Template:Rp
Interlopers
A number of interlopers have been identified, which share the same orbital elements as the true family members, but can not have come from the same breakup because of spectral (hence, compositional) differences. The following have been identified in a spectral survey: 85 Io, 141 Lumen, 546 Herodias.<ref name="Lazzaro 1999"/><ref name="Cellino-2002" />Template:Rp