 Ida has a moon named Dactyl , official designation ( 243 ) Ida I Dactyl ( / ˈdæktᵻl / DAK @-@ til ) . It was discovered in images taken by the Galileo spacecraft during its flyby in 1993 . These images provided the first direct confirmation of an asteroid moon . At the time , it was separated from Ida by a distance of 90 kilometres ( 56 mi ) , moving in a prograde orbit . Dactyl is heavily cratered , like Ida , and consists of similar materials . Its origin is uncertain , but evidence from the flyby suggests that it originated as a fragment of the Koronis parent body . 
