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Asteroid 243, a member of the Koronis family, measuring 58 km by 23 km. Close-up images of Ida were obtained on 28 August 1993 by the Galileo spacecraft en route to Jupiter. Galileo discovered that Ida has a small satellite, subsequently named Dactyl, which measures about 1.6 km by 1.2 km. Observations of Dactyl's orbital motion made it possible to determine that Ida's density lies in the range 2.2-2.9 g/cm3. The two bodies do not have an identical composition, suggesting that the system may result from the collision and break-up of larger bodies that created the Koronis family. The surfaces of both bodies are heavily cratered.
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