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Images sent back from the Galileo spacecraft provide hard evidence that asteroids can have satellites, according to a letter published in Nature magazine Wednesday.

Clark R. Chapman, of the Planetary Science Institute in Tucson, Arizona, and colleagues have studied images of the asteroid 243 Ida and found a satellite, named Dactyl, with a diameter of one mile, around it.The scientists said astronomical observations at the time a star is eclipsed by an asteroid suggested asteroids might be circled by satellites, but up to now there has been little hard evidence to back this up.

They said that Dactyl physically resembles Ida and other members of the Koronis asteroid family some 280 million miles from the sun and may have been formed when the Koronis parent body broke up.

Dactyl is slightly less red than the Ida asteroid, but the color differences are of a similar magnitude to variations among various Koronis family members, they said.