Ida was the second asteroid to be observed close-up by a spacecraft, when the Space Probe Galileo took pictures as it flew by on Aug 28, 1993. These pictures showed not only that Ida has a cratered surface, but also that it has a small moon, called Dactyl, which is about 1.6 x 1.2 km in diameter and orbiting 90 km away from the asteroid.
Source: tatoeba (6293894)