45 Eugenia

Petit-Prince orbiting Eugenia

Petit-Prince orbiting Eugenia
Image credit: Canada-France-Hawaii Telescope.

45 Eugenia is a main-belt asteroid around which, in 1998, a satellite was discovered – the first such discovery using a ground-based telescope. The little moon, named Petit-Prince, is about 13 kilometers in diameter, and travels around Eugenia in a 5-day circular orbit at a distance of about 1,190 kilometers. The orbit of the moon yields the mass of the main asteroid and hence its density, which turns out to be surprisingly low – only about 1.2 times that of water. Two possible explanations exist for this low density: either the asteroid is made mostly of ice, or it is made of rocks with big gaps in between. Because most asteroids, including Eugenia, are very dark, they cannot have icy surfaces. Eugenia might, however, be the burned-out remains of a comet, with a dark coating and an icy interior. The more popular view, though, is that it is a rubble-pile asteroid – a highly porous jumble of fairly loose rocks.


diameter 226 km
spectral class FC
rotational period 5.699 hr
semimajor axis 2.721 AU
eccentricity 0.083
inclination 6.61°
period 4.49 years