Secondary fragmentation of the Solar and Heliospheric Observatory sungrazing comets at very large heliocentric distance

The temporal distribution of the Kreutz group of sungrazing comets has been known to have an episodic character on timescales from weeks to tens of ye ars. With the large number of minor members of this group being nowadays di scovered in images taken with the Solar and Heliospheric Observatory corona graphs, it has become apparent that the distribution of these faint comets is episodic on a much shorter timescale, with objects arriving in pairs dur ing a small fraction of a day. It is shown that the rate of these pairs is much too high for a random sample. Their existence is readily explained as a result of secondary, low-velocity, nontidal fragmentation episodes, which occur virtually spontaneously at very large heliocentric distances and inv olve the products of near-perihelion splitting of progenitor fragments duri ng their previous return to the Sun. In fact, the pairs are merely extreme manifestations of larger clusters of such subnuclei, with a complex hierarc hy of fragments. Each cluster is an outcome of a sequence of nontidal fragm entation events, which begins-after the initial tidal breakup-at some point along the outbound leg of the orbit and then continues episodically to and past aphelion. A similar scenario of posttidal progressive disintegration was firmly established for comet Shoemaker-Levy 9, based on extensive obser vations of its secondary and tertiary nuclei during many months preceding t he comet's collision with Jupiter. Also, there are similarities with the me chanism proposed recently for the formation of striations in the dust tail of comet Hale-Bopp, and a logical extension of this process is the evolutio n of comet dust trails.