Hirayama families

Hirayama families

(hee-rah-yah -mah) Groupings of asteroids whose members orbit at approximately the same distance from the Sun and have very similar orbital characteristics (period, eccentricity, inclination). More than 40 families are recognized, some containing more than 70 members. They are named after the Japanese astronomer Kiyotsugu Hirayama who discovered the first nine families in 1918. It is believed that each family represents debris resulting from a collision between larger asteroids in the past. In contrast, the Amor group and the Apollo group each comprise asteroids with a range of orbital characteristics. A large number of asteroids are members of Hirayama families.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006