While en route to Jupiter, NASA’s Galileo spacecraft performed a flyby of the asteroid Ida in 1993. On 17 February 1994 examination of the images from the flyby revealed Ida, which is 53.6 km along its longest axis, has its own natural satellite. Dactyl measures just 1.6 x 1.4 x 1.2 km in diameter and orbits Ida once every 20 hours.