45 Eugenia

Eugenia was discovered on 27 June 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 6th arrondissement of Paris.^[13] It was the 45th 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 Eugénie de 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]

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-degree uncertainty,^[6] which gives it an axial tilt of 117°. Eugenia's rotation is then retrograde, rotating backward to its orbital plane.

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. It orbits the asteroid at about ~700 km, with an orbital period of 4.7 days.^[18]

• Dactyl and Ida, another asteroid and asteroid moon system catalogued by astronomers
• Florence, another dual-moon asteroid confirmed only in September 2017