It's around 50km long.  The asteroid has a moon called Dactyl that you can to the right that's about 1.5km in diameter and orbits it at around 90km.Â
Pictures taken in 1993 by the Galileo spacecraft en route to Jupiter. Â This is when Dactyl was discovered. Â Ida itself was discovered in 1884.
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Even asteroids have moons.