An adaptive optics system was used with the CFHT, located atop Mauna Kea, Hawaii, to counteract the blurring effect of Earth's atmosphere making possible this premier discovery from a ground-based telescope. Only one other asteroid-moon system is known. Dactyl, moon of the asteroid Ida, was discovered by the Galileo spacecraft during a 1993 flyby. Eugenia's moon has a nearly circular orbit with a radius of 1,190 kilometers which it completes once in 4.7 days. Knowing the moon's orbit allows astronomers to calculate the asteroid's mass.
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