Tiny moon spotted
orbiting asteroid
It was a special telescope atop
By Rod Thompson
Mauna Kea that enabled
the rare discovery
Star-BulletinHILO -- Using the Canada-France-Hawaii Telescope on Mauna Kea, astronomers have discovered a rare, tiny moon orbiting an asteroid between Mars and Jupiter.
The finding follows the recent announcement of three new moons with irregular orbits around the planet Uranus, also discovered with the CFH Telescope.
Astronomers had been searching for tiny moons around asteroids for about two decades, but the only one previously found was discovered by accident when the spacecraft Galileo flew by the asteroid Ida in 1983 and discovered the moon Dactyl.
The newest one, still unnamed and orbiting around the asteroid Eugenia, was discovered by astronomer Bill Merline from the Southwest Research Institute in Colorado.
About 300 asteroids were identified over a three-year period as being good candidates to look at, primarily because they were bright and relatively near Earth, Merline said.
Looking at an irregularly shaped asteroid called Eugenia in November of last year, Merline was able to distinguish a tiny point of light near it which was eventually confirmed to be orbiting the asteroid.
Merline described Eugenia as the similar in shaped to a potato that has been stepped on.
Although irregular in shape, it has an average diameter of 134 miles.
Astronomers weren't able to see a clear picture of the object orbiting about 7,745 miles from Eugenia. But they took an educated guess at its size -- about 8 miles across -- by comparing the amount of light Eugenia reflects to the amount of light coming from the moon.
The discovery was made possible because of a set of devices attached to the CFH Telescope that distort light to account for the Earth's atmosphere.
CFH Telescope astronomer Christian Veillet said the telescope is one of the few in the world with what's called an adaptive optics system. Merline said that's why his team came to Hawaii.
Light gathered from the telescope's 12-foot-wide main mirror of the CFH Telescope is compressed down to another mirror about 5 inches in diameter, Merline said. Computers then make tiny distortions in the small mirror to erase the distortion caused by the Earth's atmosphere.
A separate team of astronomers using the CFH Telescope discovered three new tiny moons around the planet Uranus this spring, Veillet said.
The moons discovered are all called "irregular" because their orbits are not round like normal satellite orbits, or they are steeply inclined to the equator of the plant, which is also unusual.
