Discoverer

H. Goldschmidt - 1857

Diameter (km)

214

Mass (kg)

6.1*10^{^15}

Rotation period (hrs)

5.699

Orbital period (yrs)

4.49

Semimajor axis (AU)

2.72086

Orbital eccentricity

0.08308

Orbital Inclination (deg)

6.61052

Albedo

0.04

Type

FC

Named by the discoverer in honor of the French empress and Spanish noble- woman Eugenia de Montijo, wife of Napoleon III. This is the first example of assigning the name of a human being to a minor planet. Satellite provisional designation was S/1998(45)1, the first Satellite of asteroid 45 that was discovered during 1998. Now is named Petit-Prince after the son of Eugenie.

An international team of astronomers has discovered a moon orbiting the asteroid 45 Eugenia. The pictures, taken with the Canada-France-Hawaii Telescope (CFHT) on Mauna Kea, Hawaii, are the first images of an asteroidal satellite taken from Earth. In addition, ground-based astronomers have a growing list of asteroids whose light curves look like eclipsing binaries. The strongest cases involve three other small Earth-crossers, 3671 Dionysus, 2000 DP107, 1996 FG3 and main belt asteroids: 90 Antiope, 762 Pulcova. Solar-system specialists nowsuspect that asteroid satellites are hardly rare and may in fact be common.

Previous attempts to photograph such satellites, using both ground-based telescopes and the Hubble Space Telescope, found no satellites. The only other such picture came from an interplanetary spacecraft, Galileo, when it discovered the small moon, now known as Dactyl, around asteroid 243 Ida in 1993. The observations could only be accomplished because of a new technique, called adaptive optics, that reduces the blurring caused by the Earth's atmosphere.

A surprising result of this discovery is the very low density of the primary asteroid only about 20 percent denser than water. Most asteroids appear dark and were thought to be composed primarily of rock, which is about three times denser than water.

A recent flyby of the NEAR spacecraft confirmed that another asteroid, 253 Mathilde, also has a low density. These objects are highly porous rubble-piles of rock, or they are mostly water ice.

The presence of a moon allows scientists to determine the mass of an asteroid because of the effect of the primary asteroid's gravity on its small moon. The size of most asteroids is known from standard astronomical studies. If both the mass and the size are known, researchers can learn the asteroid's density. The density then gives a clue to the asteroid's makeup either in terms of composition or structure. Except for a few of the very largest asteroids, this is the only way that asteroid densities can be determined other than by spacecraft flybys. The results are the first from a program to search for satellites around nearly 200 asteroids.

It is almost certain that the satellite was formed by a collision.As we know from the formation of our own moon and the craters on planetary surfaces, collisions played a large role in the formation of our solar system. Satellites of asteroids give us a window into these collisions, and help us understand how and why our solar system looks like it does.

The light from stars and other celestial objects is distorted by the atmosphere, much as water distorts our view of an underwater object. The new technique, pioneered at the University of Hawaii by team member Dr. Francois Roddier, analyzes the distortions and corrects the light beam by means of what is essentially a "fun-house mirror" back into its previous, undistorted form. "CFHT's exceptional site, telescope, and adaptive optics now allow us to see far sharper detail through the Earth's atmosphere. In many cases we can now compete with the clarity of space-based telescopes," said Roddier. The instrument used was built by the CFHT Corporation.

Previously, faint and close satellites would have been lost in the glare of the primary asteroid.

Eugenia orbits the sun in the main asteroid belt, a collection of thousands of asteroids that exists between the orbits of Mars and Jupiter. Asteroids are thought to be bodies that never formed a planet; the gravity of the giant planet Jupiter may have stirred up the bodies enough that they collided with each other at fast speeds, perhaps either fragmenting or forming satellites, rather than colliding gently, adhering, and gradually building up a planet.

Researchers estimate that the diameter of the satellite is about 13 kilometers. Eugenia's diameter is about 215 kilometers. The researchers have determined that the satellite has a circular orbit about 1,190 km away from Eugenia. It orbits about once every five days.

Images of Eugenia