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 km in diameter, and travels around Eugenia in a 5-day circular
orbit at a distance of about 1,190 km. 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.
|Petit-Prince orbiting Eugenia
Image credit: Canada-France-Hawaii Telescope
ASTEROIDS, CENTAURS, AND KUIPER BELT OBJECTS