The problem of split comets revisited

The results fromstudies ofD/Shoemaker–Levy9 and other recent split comets and comet pairs lead to the recognition of fundamental differences between breakupproducts of the tidally and the nontidally split comets and to the conclusive identification of the so-called dissipating comets as secondary nuclei of previously split comets, whose separately arriving principal nuclei had in most cases been missed. The primary attribute of the nontidally split comets is the leading position of the principal nucleus, with all the companion nuclei trailing behind, eventually along the orbit. No such configuration has been observed for the tidally split comets ofmore than two components. Dominant effects in the relativemotions of fragments derived from the tidal disruptions are due to separation velocities, while differential decelerations (due, presumably, to outgassing-driven nongravitational perturbations) prevail for fragments derived from the nontidal breakups. This diversity is interpreted in terms of major differences between the breakup mechanisms for the two categories of objects and between the resulting mass distributions of fragments.