More than 40 split comets have been observed over the past 150 years. Two of the split comets have disappeared completely; another one was destroyed during its impact on Jupiter. The analysis of the postsplitting dynamics of fragments suggests that nucleus splitting can occur at large heliocentric distances (certainly beyond 50 AU) for long-period and new comets and all along the orbit for short-period comets. Various models for split comets have been proposed, but only in one peculiar case, the break-up of Comet D/1993 F2 (Shoemaker-Levy 9) around Jupiter, has a splitting mechanism been fully understood: The nucleus of D/1993 F2 was disrupted by tidal forces. The fragments of split comets seem to be subkilometer in size. It is, however, not clear whether they are cometesimals that formed during the early formation history of the planetary system or are pieces from a heavily processed surface crust of the parent body. The two basic types of comet splitting (few fragments and many fragments) may require different model interpretations. Disappearing comets may represent rare cases of complete nucleus dissolution as suggested by the prototype case, Comet C/1999 S4 (LINEAR). At least one large family of split comets exists - the Kreutz group- but other smaller clusters of comets with common parent bodies are very likely. Comet splitting seems to be an efficient process of mass loss of the nucleus and thus can play an important role in the evolution of comets toward their terminal state. The secondary nuclei behave as comets of their own (with activity, coma, and tail) exhibiting a wide range of lifetimes. However, at present it is now known whether the fragments' terminal state is "completely dissolved" or "exhausted and inactive."
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