Astronomers sight an asteroid's moon

October 06, 1999

Astronomers this week announced their discovery of a moon orbiting an asteroid, in the first images ever obtained of such an object from Earth. Only one satellite orbiting an asteroid had been seen before from space.

In work supported by the National Science Foundation (NSF) and NASA, an international team headed by William Merline of the Southwest Research Institute sighted a moon orbiting the asteroid (45) Eugenia, in the main asteroid belt between Mars and Jupiter. The images will be published in the October 7 issue of Nature.

"Making this discovery with the newly developed adaptive optics moves ground-based astronomy to the forefront in exploring neighboring objects in our solar system," said Vernon Pankonin, manager of NSF's planetary astronomy program.

Merline's team plans to sample about 200 asteroids for potential satellites using ground-based telescopes with adaptive optics, a recent technology that corrects for the distortions caused by the Earth's atmosphere. Eugenia's moon was found with the Canada-France-Hawaii telescope, fitted with adaptive optics, on Mauna Kea, Hawaii.

This discovery helps answer questions about the formation of objects in our solar system. Observing the moon and the asteroid's gravitational pull on it helped scientists determine that the asteroid was less dense than anticipated, indicating that asteroids may not be composed primarily of rock as once thought. The moon was probably created by a collision.

The only other sighting of an asteroid's satellite was by the interplanetary spacecraft Galileo, when it found a moon around asteroid (243) Ida in 1993.
Editors -- images of Eugenia's moon will be available at 2:00 p.m.EDT at:

National Science Foundation

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