15 Eunomia
15 Eunomia is a very big asteroid in the closer part of the main asteroid belt. It is the biggest of the stony (S-type) asteroids, and somewhere between the 8th to 12th biggest Main Belt asteroid overall (unsure diameters make its ranking unsure). It is also the biggest member of the Eunomia family of asteroids.
| Discovery | |
|---|---|
| Discovered by | Annibale de Gasparis |
| Discovery date | July 29, 1851 |
| Designations | |
| none | |
| Main belt, (Eunomia family) | |
| Orbital characteristics | |
| Epoch June 14, 2006 (JD 2453900.5) | |
| Aphelion | 469.429 Gm (3.138 AU) |
| Perihelion | 321.429 Gm (2.149 AU) |
| 395.429 Gm (2.643 AU) | |
| Eccentricity | 0.187 |
| 1569.687 d (4.30 a) | |
Average orbital speed | 18.16 km/s |
| 286.102° | |
| Inclination | 11.738° |
| 293.273° | |
| 97.909° | |
| Physical characteristics | |
| Dimensions | 330×245×205[1][2][3] |
| Mass | 3.26±0.12×1019 kg[4] |
Mean density | 3.8±0.7 g/cm³ |
| 0.08 m/s² | |
| 0.16 km/s | |
| 0.2535 d (6.083 h)[5] | |
| Albedo | 0.209 (geometric)[1] |
| Temperature | ~166 K max: 260 K (-13 °C) |
Spectral type | S-type asteroid |
| 7.9[6] to 11.24 | |
| 5.28 | |
| 0.29" to 0.085" | |
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Eunomia was found 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.
Characteristics
As the biggest S-type asteroid (with 3 Juno being a very close second), Eunomia has attracted a moderate amount of scientific attention. It has a bit over one percent of the mass of the entire main belt.
Eunomia appears to be a stretched but fairly round body, with what appear to be four sides of differing curvature and noticeably different average compositions.[2] Its stretched shape led to the suggestion that Eunomia may be a binary object. However, this has been denied.[3] It is a retrograde rotator with its pole pointing towards ecliptic coordinates (β, λ) = (-65°, 2°) with a 10° uncertainty.[2][3] This gives an axial tilt of about 165°.
Like other true members of the family, its surface is made up 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 made up differently.
Eunomia has been seen occulting stars three times. It has a mean opposition magnitude of +8.5,[7] about equal to the mean brightness of Titan and can reach +7.9 at a near perihelion opposition.
References
- ↑ 1.0 1.1 Supplemental IRAS Minor Planet Survey
- ↑ 2.0 2.1 2.2 Nathues, A.; et al.; (2005); Spectral study of the Eunomia asteroid family - I. Eunomia, Icarus, Vol. 175, p. 452
- ↑ 3.0 3.1 3.2 Tanga, P.; et al.; (2003); Asteroid observations with the Hubble Space Telescope; Astronomy & Astrophysics, Vol. 401, p. 733
- ↑ Stoss, R. M; Vitagliano, A. (2006). "Astronomy & Astrophysics manuscript no. aa5760-06" (PDF). Archived from the original (PDF) on 2008-12-03.
- ↑ "Planetary Data System (PDS) lightcurve data". Archived from the original on 2006-06-14. Retrieved 2007-12-18.
- ↑ Donald H. Menzel and Jay M. Pasachoff (1983). A Field Guide to the Stars and Planets (2nd ed.). Boston, MA: Houghton Mifflin. p. 391. ISBN 978-0-395-34835-2.
- ↑ "The Brightest Asteroids". Archived from the original on 2010-01-17. Retrieved 2007-12-18.