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Discovering Dactyl

When the Galileo spacecraft flew past Ida in 1993, no one expected to find a moon. Its discoverer recalls how it happened.
Editor's note: On August 28, 1993, the Galileo spacecraft — on its way toward Jupiter to begin a successful 8-year mission — flew past asteroid 243 Ida. It was Galileo's second asteroid flyby, following an October 1991 encounter with 951 Gaspra. But Ida had a big surprise: a 1-mile-wide (1.6 kilometer) moon was found orbiting the 35-mile-diameter (56 km) main-belt asteroid. Ann Harch, an assistant science coordinator on Galileo's imaging team, discovered the moon. This is her story.

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