Following anomalous sightings during an occultation of the star SAO 1220774 in 1978 , Herculina became the first asteroid to be `` confirmed '' to have an asteroid moon , with the parent asteroid estimated at a 216km diameter and a moon of about 45km orbiting at a distance of around 1,000 km . Following anomalous observations during an occultation of the star SAO 120774 in 1978 , Herculina became the first asteroid to be `` confirmed '' to have an asteroid moon , with the parent asteroid estimated at a 216 km diameter and a satellite of about 45 km orbiting at a distance of around 1,000 km .