Asteroid Ida and its Dactyl moon

243 Ida is the second asteroid visited by a spacecraft and the first found to have its own moon. Its close encounter happened on 29 August 1993 as Galileo flew by at a distance of about 1,500 miles (about 2,400 kilometers) en route to Jupiter. (The spacecraft flew by another asteroid, Gaspra, on Oct. 29, 1991.) A little more than five months later, scientists studying the images Galileo sent back to Earth noticed that a tiny moon accompanied the asteroid.