45 Eugenia

**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.

### 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.

## Other websites

- Johnston Archive data
- Astronomical Picture of Day 14 October 1999
- SwRI Press Release
- Orbit of Petit-Prince, companion of Eugenia
- IAUC 8177
- Shape model derived from lightcurve (on page 17)

## Infobox (planet)

- **bgcolour**: #FFFFC0
- **minorplanet**: yes
- **name**: 45 Eugenia
- **discoverer**: Hermann Mayer Salomon Goldschmidt, H. Goldschmidt
- **discovered**: 27 June 1857
- **alt names**: 1941 BN
- **mp category**: Main belt
- **epoch**: November 26, 2005 (Julian day, JD 2453701.5)
- **semimajor**: 406.897 Giga, Gmetre, m (2.720 Astronomical unit, AU)
- **perihelion**: 373.488 Gm (2.497 AU)
- **aphelion**: 440.305 Gm (2.943 AU)
- **eccentricity**: 0.082
- **period**: 1638.462 day, d (4.49 Julian year (astronomy), a)
- **inclination**: 6.610degree (angle), °
- **asc node**: 147.939°
- **arg peri**: 85.137°
- **mean anomaly**: 45.254°
- **avg speed**: 18.03 km/second, s
- **satellites**: Petit-Prince (moon), Petit-Prince
S/2004 (45) 1
- **dimensions**: 305×220×145 km
- **mean radius**: 107.3 ± 2.1 km
- **mass**: 5.8 ± 0.2  kilogram, kg
- **density**: 1.1 ± 0.3 gram, g/cubic centimetre, cm³
- **surface grav**: 0.017 m/s²
- **escape velocity**: 0.071 km/s
- **sidereal day**: 0.2375 d (5.699 hour, h)
- **axial tilt**: 117 ± 10°
- **pole ecliptic lat**: -30 ± 10°
- **pole ecliptic lon**: 124 ± 10°
- **temp name1**: Kelvin
- **mean temp 1**: ~171
- **max temp 1**: 253
- **temp name2**: Celsius
- **max temp 2**: -22°
- **albedo**: 0.040 ± 0.002
- **spectral type**: F-type asteroid, F
- **abs magnitude**: 7.46