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45 Eugenia

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45 Eugenia

45 Eugenia
CFHT time-lapse image of Eugenia and Petit-Prince, showing five stages in the moon's orbit. The 'flare' around them is an imaging artifact
Discovered by H. Goldschmidt
Discovery date 27 June 1857
Named after
Empress Eugénie
1941 BN
Main belt
Orbital characteristics[2]
Epoch November 26, 2005 (JD 2453701.5)
Aphelion 440.305 Gm (2.943 AU)
Perihelion 373.488 Gm (2.497 AU)
406.897 Gm (2.720 AU)
Eccentricity 0.082
1638.462 d (4.49 a)
Average orbital speed
18.03 km/s
Inclination 6.610°
Known satellites Petit-Prince
S/2004 (45) 1
Physical characteristics
Dimensions 232 × 193 × 161 km[3]
305 × 220 × 145 km[4][5]
Mean radius
107.3 ± 2.1 km[4]
Mass (5.69 ± 0.1) ×1018 kg[3]
(5.8 ± 0.2) ×1018 kg[6][7][8]
Mean density
1.1 ± 0.1 g/cm³[3]
1.1 ± 0.3 g/cm³[7]
Equatorial surface gravity
0.017 m/s²[9]
Equatorial escape velocity
0.071 km/s[9]
Sidereal rotation period
0.2375 d (5.699 h)[10]
117 ± 10°
-30 ± 10°[5]
124 ± 10°
0.040 ± 0.002[4]
Surface temp. min mean max
Kelvin ~171 253
Celsius -22°

45 Eugenia is a large asteroid of the asteroid belt. It is famed as one of the first asteroids to be found to have a moon orbiting it. It is also the second known triple asteroid, after 87 Sylvia.


  • Discovery 1
  • Physical characteristics 2
  • Satellite system 3
    • Petit-Prince 3.1
    • S/2004 (45) 1 3.2
  • See also 4
  • References 5
  • External links 6


Eugenia was discovered on June 28, 1857 by the Franco-German amateur astronomer Hermann Goldschmidt.[12] His instrument of discovery was a 4-inch aperture telescope located in his sixth floor apartment in the Latin Quarter of Paris.[13] It was the forty-fifth minor planet to be discovered. The preliminary orbital elements were computed by Wilhelm Forster in Berlin, based on three observations in July, 1857.[14]

The asteroid was named by its discoverer after Empress Eugenia di Montijo, the wife of Napoleon III.[12] It was the first asteroid to be definitely named after a real person, rather than a figure from classical legend,[15] although there was some controversy about whether 12 Victoria was really named for the mythological figure or for Queen Victoria.

Physical characteristics

Eugenia is a large asteroid, with a diameter of 214 km. It is an F-type asteroid, which means that it is very dark in colouring (darker than soot) with a carbonaceous composition. Like Mathilde, its density appears to be unusually low, indicating that it may be a loosely-packed rubble pile, not a monolithic object. Eugenia appears to be almost anhydrous.[16] Lightcurve analysis indicates that Eugenia's pole most likely points towards ecliptic coordinates (β, λ) = (-30°, 124°) with a 10° uncertainty,[5] which gives it an axial tilt of 117°. Eugenia's rotation is then retrograde.

Satellite system


In November 1998, astronomers at the Canada-France-Hawaii Telescope on Mauna Kea, Hawaii, discovered a small moon orbiting Eugenia. This was the first time an asteroid moon had been discovered by a ground-based telescope. The moon is much smaller than Eugenia, about 13 km in diameter, and takes five days to complete an orbit around it.

The discoverers chose the name "Petit-Prince" (formally "(45) Eugenia I Petit-Prince"). This name refers to Empress Eugenia's son, the Prince Imperial. However, the discoverers also intended an allusion to the children's novella The Little Prince by Antoine de Saint-Exupéry, which is about a young prince who lives on an asteroid.[17]

S/2004 (45) 1

A second, smaller (estimated diameter of 6 km) satellite that orbits closer to Eugenia than Petit-Prince has since been discovered and provisionally named S/2004 (45) 1.[18] It was discovered by analyses of three images acquired in February 2004 from the 8.2 m VLT "Yepun" at the European Southern Observatory (ESO) Cerro Paranal, in Chile.[19] The discovery was announced in IAUC 8817, on 7 March 2007 by Franck Marchis and his IMCCE collaborators. It orbits the asteroid at about ~700 km, with an orbital period of 4.7 days.[18]

See also


  1. ^ "Discovery Circumstances: Numbered Minor Planets". IAU Minor Planet Center. Harvard-Smithsonian Center for Astrophysics. February 9, 2010. Archived from the original on 17 August 2010. Retrieved 2010-08-12. 
  2. ^ "ASTORB". Orbital elements database.  
  3. ^ a b c Baer, Jim (2008). "Recent Asteroid Mass Determinations". Personal Website. Retrieved 2008-12-07. 
  4. ^ a b c d "Supplemental IRAS Minor Planet Survey". 
  5. ^ a b c Kaasalainen, M.; et al. (2002). "Models of Twenty Asteroids from Photometric Data" (PDF). Icarus 159 (2): 369–395.  
  6. ^ Marchis, F. "synthesis of several observations". Berkeley. 
  7. ^ a b Marchis, F.; et al. (2004). "Fine Analysis of 121 Hermione, 45 Eugenia, and 90 Antiope Binary Asteroid Systems With AO Observations". Bulletin of the American Astronomical Society 36: 1180.  
  8. ^ Uncertainty calculated from uncertainties in the orbit of Petit-Prince.
  9. ^ a b On the extremities of the long axis.
  10. ^ "PDS lightcurve data". Planetary Science Institute. 
  11. ^ "PDS node taxonomy database". Planetary Science Institute. 
  12. ^ a b Schmadel, Lutz D. (2003). Dictionary of minor planet names. Physics and astronomy online library (5th ed.). Springer. p. 19.  
  13. ^ J. C. (1867). "Memoirs of the Royal Astronomical Society". Memoirs of the Royal Astronomical Society (Priestley and Weale) 36: 155. Retrieved 2010-08-13. 
  14. ^ Goldschmidt, H. (July 1857). "New Planet (45)".  
  15. ^ Tobin, William (2003). The life and science of Léon Foucault: the man who proved the earth rotates. Cambridge University Press. p. 301.  
  16. ^ A. S. Rivkin (2002). "Calculated Water Concentrations on C Class Asteroids" (PDF). Lunar and Planetary Institute. Retrieved 2008-05-22. 
  17. ^ William J. Merlin et al, "On a Permanent Name for Asteroid S/1998(45)1". May 26, 2000.
  18. ^ a b IAUC 8817
  19. ^ IMCCÉ Breaking News

External links

  • Johnston Archive data
  • Astronomical Picture of Day 14 October 1999
  • SwRI Press Release
  • Orbit of Petit-Prince, companion of Eugenia
  • Shape model derived from lightcurve (on page 17)
  • 14 frames of (45) Eugenia primary taken with the Keck II AO from Dec 2003 to Nov 2011 (Franck Marchis)
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