45 Eugenia

Eugenia (minor planet designation: 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.

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.
Discovery[1]
Discovered byH. Goldschmidt
Discovery date27 June 1857
Designations
(45) Eugenia
Pronunciation/juːˈdʒiːniə/[2]
Named after
Empress Eugénie
1941 BN
Main belt
AdjectivesEugenian
Orbital characteristics[3]
Epoch 26 November 2005 (JD 2453701.5)
Aphelion440.305 Gm (2.943 AU)
Perihelion373.488 Gm (2.497 AU)
406.897 Gm (2.720 AU)
Eccentricity0.082
1638.462 d (4.49 a)
45.254°
Inclination6.610°
147.939°
85.137°
Known satellitesPetit-Prince
S/2004 (45) 1
Physical characteristics
Dimensions232 × 193 × 161 km[4]
305 × 220 × 145 km[5][6]
Mean radius
107.3 ± 2.1 km[5]
Mass(5.69 ± 0.1) ×1018 kg[4]
(5.8 ± 0.2) ×1018 kg[7][8][9]
Mean density
1.1 ± 0.1 g/cm³[4]
1.1 ± 0.3 g/cm³[8]
Equatorial surface gravity
0.017 m/s²[10]
Equatorial escape velocity
0.071 km/s[10]
0.2375 d (5.699 h)[11]
117±10°
−30±10°[6]
124±10°
0.040±0.002[5]
F[12]
7.46[5]

    Discovery

    Eugenia was discovered on 27 June 1857 by the Franco-German amateur astronomer Hermann Goldschmidt.[13] His instrument of discovery was a 4-inch aperture telescope located in his sixth floor apartment in the 6th Arrondissement of Paris.[14] 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.[15]

    The asteroid was named by its discoverer after Empress Eugenia di Montijo, the wife of Napoleon III.[13] It was the first asteroid to be definitely named after a real person, rather than a figure from classical legend.[16]

    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.[17] Lightcurve analysis indicates that Eugenia's pole most likely points towards ecliptic coordinates (β, λ) = (-30°, 124°) with a 10° uncertainty,[6] which gives it an axial tilt of 117°. Eugenia's rotation is then retrograde, rotating backward to its orbital plane.

    Satellite system

    Petit-Prince
    Main article: Petit-Prince (moon)

    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.[18]

    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.[19] 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.[20] 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.[19]

    See also

    References
    1. "Discovery Circumstances: Numbered Minor Planets". IAU Minor Planet Center. Harvard-Smithsonian Center for Astrophysics. 9 February 2010. Archived from the original on 10 May 2008. Retrieved 12 August 2010.
    2. "Eugenia". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
    3. "ASTORB". Orbital elements database. Lowell Observatory.
    4. Baer, Jim (2008). "Recent Asteroid Mass Determinations". Personal Website. Archived from the original on 2 July 2013. Retrieved 7 December 2008.
    5. "Supplemental IRAS minor planet survey". Planetary Science Institute. Archived from the original on 17 August 2009.
    6. Kaasalainen, M.; et al. (2002). "Models of Twenty Asteroids from Photometric Data" (PDF). Icarus. 159 (2): 369–395. Bibcode:2002Icar..159..369K. doi:10.1006/icar.2002.6907.
    7. Marchis, F. "synthesis of several observations". Berkeley. Archived from the original on 13 September 2006.
    8. 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. Bibcode:2004DPS....36.4602M.
    9. Uncertainty calculated from uncertainties in the orbit of Petit-Prince.
    10. On the extremities of the long axis.
    11. "PDS lightcurve data". Planetary Science Institute. Archived from the original on 9 April 2009.
    12. "PDS node taxonomy database". Planetary Science Institute. Archived from the original on 5 August 2009.
    13. Schmadel, Lutz D. (2003). Dictionary of minor planet names. Physics and astronomy online library (5th ed.). Springer. p. 19. ISBN 3-540-00238-3.
    14. J. C. (1867). "Memoirs of the Royal Astronomical Society". Memoirs of the Royal Astronomical Society. Priestley and Weale. 36: 155. Retrieved 13 August 2010.
    15. Goldschmidt, H. (July 1857). "New Planet (45)". Monthly Notices of the Royal Astronomical Society. 17: 263–264. Bibcode:1857MNRAS..17..263G. doi:10.1093/mnras/17.9.263b.
    16. Tobin, William (2003). The life and science of Léon Foucault: the man who proved the earth rotates. Cambridge University Press. p. 301. ISBN 0-521-80855-3.
    17. A. S. Rivkin (2002). "Calculated Water Concentrations on C Class Asteroids" (PDF). Lunar and Planetary Institute. Retrieved 22 May 2008.
    18. William J. Merlin et al., "On a Permanent Name for Asteroid S/1998(45)1". 26 May 2000.
    19. Marchis, F.; Baek, M.; Descamps, P.; Berthier, J.; Hestroffer, D.; Vachier, F. (2007). "S/2004 (45) 1". IAU Circular. 8817. Bibcode:2007IAUC.8817....1M.
    20. "IMCCÉ Breaking News". Archived from the original on 27 September 2007. Retrieved 30 April 2019.

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