15 Eunomia

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15 Eunomia Astronomical symbol for 15 Eunomia
Discovered byAnnibale de Gasparis
Discovery dateJuly 29, 1851
Main belt, (Eunomia family)
Orbital characteristics
Epoch June 14, 2006 (JD 2453900.5)
Aphelion469.429 Gm (3.138 AU)
Perihelion321.429 Gm (2.149 AU)
395.429 Gm (2.643 AU)
1569.687 d (4.30 a)
18.16 km/s
Physical characteristics
Mass3.26±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]
Albedo0.209 (geometric)[1]
Temperature~166 K
max: 260 K (-13 °C)
Spectral type
S-type asteroid
7.9[6] to 11.24
0.29" to 0.085"

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.

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[change | change source]

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[change | change source]

  1. 1.0 1.1 Supplemental IRAS Minor Planet Survey
  2. 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. 3.0 3.1 3.2 Tanga, P.; et al.; (2003); Asteroid observations with the Hubble Space Telescope; Astronomy & Astrophysics, Vol. 401, p. 733
  4. Stoss, R. M.; Vitagliano, A.; (2006); New mass determination of (15) Eunomia based on a very close encounter with (50278) 2000 CZ12; Astronomy & Astrophysics manuscript no. aa5760-06
  5. Planetary Data System (PDS) lightcurve data[dead link]
  6. Donald H. Menzel and Jay M. Pasachoff (1983). A Field Guide to the Stars and Planets (2nd edition ed.). Boston, MA: Houghton Mifflin. p. p. 391. ISBN 978-0-395-34835-2.CS1 maint: Extra text (link)
  7. The Brightest Asteroids Archived 17 January 2010 at WebCite

Other websites[change | change source]