Also found in: Wikipedia.
Themis family(th'ee -miss) A Hirayama family of asteroids located in the outer main belt at a distance of 3.2 AU from the Sun, most members having diameters less than 60 km. They all have low albedos, are of C-type, and correspond to different metamorphic grades of carbonaceous chondrite material. These are thought to have been produced by different layers of the parent body suffering differing degrees of heating. The different types of material were then revealed when this body suffered collisional fragmentation. The Themis family is one of the most highly populated, with more than 500 members known. It takes its name from the asteroid Themis, discovered in 1853 by the Italian astronomer Annibale de Gasparis.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006