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45 Eugenia
Discovery
Discovered by H. Goldschmidt
Discovery date 27 June 1857
Designations
1941 BN
Main belt
Orbital characteristics
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)
18.03 km/s
45.254°
Inclination 6.610°
147.939°
85.137°
Known satellites Petit-Prince
S/2004 (45) 1
Physical characteristics
Dimensions 305×220×145 km
Mean radius
107.3 ± 2.1 km
Mass 5.8 ± 0.2 ×1018 kg
Mean density
1.1 ± 0.3 g/cm³
Equatorial surface gravity
0.017 m/s²
Equatorial escape velocity
0.071 km/s
0.2375 d (5.699 h)
117 ± 10°
Pole ecliptic latitude
-30 ± 10°
Pole ecliptic longitude
124 ± 10°
0.040 ± 0.002
Surface temp. min mean max
Kelvin ~171 253
Celsius -22°
F
7.46

45 Eugenia is a big Main belt asteroid. It is famous because it is 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

Eugenia was found in 1857 by Hermann Goldschmidt. It was named after Empress Eugenia di Montijo, the wife of Napoleon III, and was the first asteroid to be named after a real person, rather than a figure from classical legend (although there had been controversy about whether 12 Victoria was really named for the mythological figure or for Queen Victoria).

Physical characteristics

Eugenia is a big 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) made up of carbonate. Like Mathilde, its density appears to be unusually low, indicating that it may be a loosely-packed rubble pile (an asteroid that has been broken apart by a collision and pulled back together by gravity).

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

Moons

Petit-Prince

In November 1998, astronomers at the Canada-France-Hawaii Telescope on Mauna Kea, Hawaii, found a small moon orbiting Eugenia. This was the first time a moon orbiting an asteroid had been found by a ground-based telescope. Eugenia's moon has been named (45) Eugenia I Petit-Prince, after Empress Eugenia's son, the Prince Imperial. The moon is much smaller than Eugenia, about 13 km in diameter, and takes five days to complete an orbit around it.

S/2004 (45) 1

A second, smaller (estimated diameter of 6 km) moon that orbits closer to Eugenia than Petit-Prince has since been found and provisionally named S/2004 (45) 1. It was found 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. The discovery was announced in IAUC 8817, on 7 March 2007 by Franck Marchis and his IMCCE collaborators.

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