15 Eunomia

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15 Eunomia Astronomical symbol for 15 Eunomia
Discovery
Discovered by Annibale de Gasparis
Discovery time July 29, 1851
Names
Other names none
Group Main belt, (Eunomia family)
Orbit
Reference date June 14, 2006 (JD 2453900.5)
Longest distance from the Sun 469.429 Gm (3.138 AU)
Shortest distance from the Sun 321.429 Gm (2.149 AU)
Longest distance from the center of its orbital path
("semi-major axis")
395.429 Gm (2.643 AU)
How egg-shaped its orbit is
("eccentricity")
0.187
How long it takes to complete an orbit 1569.687 d (4.30 a)
Average speed 18.16 km/s
Mean anomaly 286.102°
Angle above the reference plane
("inclination")
11.738°
Longitude of where it comes up through the reference plane 293.273°
Angle between its shortest distance from what it orbits around and where it comes up through the reference plane
("argument of periapsis")
97.909°
Size and Other Qualities
Measures 330×245×205[1][2][3]
Mass 3.26±0.12×1019 kg[4]
Average density 3.8±0.7 g/cm³
Gravity at its surface 0.08 m/s²
Slowest speed able to escape into space
("escape velocity")
0.16 km/s
How long it takes to turn around one time 0.2535 d (6.083 h)[5]
How much light it reflects 0.209 (geometric)[1]
Avg. surface temp. ~166 K
max: 260 K (-13 °C)
Light-band group
("spectral type")
S-type asteroid
Seeming brightness
("apparent magnitude")
7.9[6] to 11.24
True brightness
("absolute magnitude")
5.28
Seeming size
("angular diameter")
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.
  7. The Brightest Asteroids Archived 17 January 2010 at WebCite

Other websites[change | change source]