15 Eunomia
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A three-dimensional model of 15 Eunomia based on its light curve
|
|
| Discovery | |
|---|---|
| Discovered by | Annibale de Gasparis |
| Discovery date | July 29, 1851 |
| Designations | |
| MPC designation | (15) Eunomia |
| Pronunciation | /jʊˈnoʊmiə/ ew-NOH-mee-ə |
|
Named after
|
Eunomia |
| none | |
| Main belt, (Eunomia family) | |
| Orbital characteristics | |
| Epoch June 14, 2006 (JD 2453900.5) | |
| Aphelion | 3.138 AU (469.429 Gm) |
| Perihelion | 2.149 AU (321.429 Gm) |
| 2.643 AU (395.429 Gm) | |
| Eccentricity | 0.187 |
| 4.30 yr (1569.687 d) | |
|
Average orbital speed
|
18.16 km/s |
| 286.102° | |
| Inclination | 11.738° |
| 293.273° | |
| 97.909° | |
| Physical characteristics | |
| Dimensions |
(357×255×212)±15 km |
| Mass | 3.12 ×1019 kg |
|
Mean density
|
3.14 ± 0.53 g/cm³ 3.8±0.7 g/cm³ (based on IRAS diameter of 255km) |
| 0.08 m/s² | |
| 0.16 km/s | |
| 0.2535 d (6.083 h) | |
| Albedo | 0.209 (geometric) |
| Temperature | ~166 K max: 260 K (-13 °C) |
|
Spectral type
|
S-type asteroid |
| 7.9 to 11.24 | |
| 5.28 | |
| 0.29" to 0.085" | |
(357×255×212)±15 km
268 km (mean)
330×245×205
15 Eunomia is a very large asteroid in the inner asteroid belt. It is the largest of the stony (S-type) asteroids, and somewhere between the 8th-to-12th-largest main-belt asteroid overall (uncertainty in diameters causes uncertainty in its ranking). It is the largest Eunomian asteroid, and is estimated to contain 1% of the mass of the asteroid belt.
Eunomia was discovered by Annibale de Gasparis on July 29, 1851, and named after Eunomia, one of the Horae (Hours), a personification of order and law in Greek mythology.
As the largest S-type asteroid (with 3 Juno being a very close second), Eunomia has attracted a moderate amount of scientific attention. It contains slightly over one percent of the mass of the entire asteroid belt.
Eunomia appears to be an elongated but fairly regularly shaped body, with what appear to be four sides of differing curvature and noticeably different average compositions. Its elongation led to the suggestion that Eunomia may be a binary object, but this has been refuted. It is a retrograde rotator with its pole pointing towards ecliptic coordinates (β, λ) = (−65°, 2°) with a 10° uncertainty. This gives an axial tilt of about 165°.
Like other true members of the family, its surface is composed of silicates and some nickel-iron, and is quite bright. Calcium-rich pyroxenes and olivine, along with nickel-iron metal, have been detected on Eunomia's surface. Spectroscopic studies suggest that Eunomia has regions with differing compositions: A larger region dominated by olivine, which is pyroxene-poor and metal-rich, and another somewhat smaller region on one hemisphere (the less pointed end) that is noticeably richer in pyroxene, and has a generally basaltic composition.
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