45 Eugenia

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45 Eugenia
45 Eugenia VLT (2021), deconvolved.pdf
Discovery [1]
Discovered by H. Goldschmidt
Discovery date27 June 1857
(45) Eugenia
Pronunciation /jˈniə/ [2]
Named after
Empress Eugénie
1941 BN
Main belt
Adjectives Eugenian
Orbital characteristics [3]
Epoch 26 November 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)
Inclination 6.610°
Known satellites Petit-Prince
S/2004 (45) 1
Physical characteristics
Dimensions232 × 193 × 161 km [4]
305 × 220 × 145 km [5] [6]
Mean radius
94±1 km [7]
107.3±2.1 km [5]
Mass (5.8±0.1)×1018 kg [7]
(5.69±0.1)×1018 kg [4]
(5.8±0.2)×1018 kg [8] [9] [10]
Mean density
1.66±0.07 g/cm3 [7]
1.1±0.1 g/cm3 [4]
1.1±0.3 g/cm3 [9]
Equatorial surface gravity
0.017 m/s² [11]
Equatorial escape velocity
0.071 km/s [11]
Sidereal rotation period
0.2375 d (5.699 h) [12]
−30±10° [6]
0.065 (calculated) [7]
0.040±0.002 [5]
F [13]
7.46 [5]

    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 was also the second triple asteroid to be discovered, after 87 Sylvia.



    Eugenia was discovered on 27 June 1857 by the Franco-German amateur astronomer Hermann Goldschmidt. [14] His instrument of discovery was a 4-inch aperture telescope located in his sixth floor apartment in the 6th Arrondissement of Paris. [15] 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. [16]

    The asteroid was named by its discoverer after Empress Eugenia di Montijo, the wife of Napoleon III. [14] It was the first asteroid to be definitely named after a real person, rather than a figure from classical legend. [17]

    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. [18] 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


    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. [19]

    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. [20] 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. [21] 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. [20]

    See also

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