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
Discovery[1] and designation
Discovered by	H. Goldschmidt
Discovery date	27 June 1857
Designations
Pronunciation	/juːˈdʒiːniə/ ew-JEE-nee-ə
Named after	Empress Eugénie
Alternative names	1941 BN
Minor planet category	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)
Semi-major axis	406.897 Gm (2.720 AU)
Eccentricity	0.082
Orbital period	1638.462 d (4.49 a)
Average orbital speed	18.03 km/s
Mean anomaly	45.254°
Inclination	6.610°
Longitude of ascending node	147.939°
Argument of perihelion	85.137°
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]
Axial tilt	117 ± 10°
Pole ecliptic latitude	-30 ± 10°[5]
Pole ecliptic longitude	124 ± 10°
Geometric albedo	0.040 ± 0.002[4]
Surface temp. min mean max Kelvin ~171 253 Celsius -22°
Spectral type	F[11]
Absolute magnitude (H)	7.46[4]

45 Eugenia is a large main-belt asteroid. 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

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.^{[citation needed]}

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

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.^[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.

See also

• Dactyl and Ida, another asteroid and asteroid moon system catalogued by astronomers

References

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)