What are often called minor planets?
Minor planets are divided into groups and families based on their orbital characteristics. Apart from the broadest divisions, it is customary to name a group of asteroids after the first member of that group to be discovered (often the largest). While so-called groups are relatively loose dynamical associations, families are much “tighter” and result usually from the catastrophic breakup of a large parent asteroid sometime in the past. Families have only been recognized within the main asteroid belt. They were first recognised by Kiyotsugu Hirayama in 1918 and are often called Hirayama families in his honor.
