Also found in: Dictionary, Thesaurus.
planetesimals(plan-ĕ-tess -ă-mălz) Bodies, ranging in size from less than a millimeter to many kilometers, that are thought to have formed the planets of the Solar System by a process of accretion.
the tiny solid particles that were the material for the formation of the planets according to the cosmogonical hypothesis advanced at the turn of the century by the American scientists F. Moulton and T. Chamberlin. The hypothesis attributed the formation of planetesimals to the cooling and condensation of matter ejected by the sun. This assumption, however, is not valid, since it is incapable of explaining the large distances and specific angular momenta of the planets. The term “planetesimal” is sometimes used in modern cosmogonical hypotheses and theories that consider the formation of the planets from solid particles.