Named in honor of Isamu Hirabayashi (b. 1941), amateur astronomer who founded the Japan Lunar and Planetary Observers Network when he was a high-school student in 1959 and who has been its president ever since. This organization soon became one of the most active groups of lunar and planetary observers and theorists in Japan. He also served as director of the Jupiter-Saturn Section of the Oriental Astronomical Association from 1971 to 1989. Name proposed by the discoverers following a suggestion by T. Sato and A. Fujii.