Comet Splitting — Observations and Model Scenarios

Abstract

Splitting events affect cometary nuclei to a different level of severity ranging from complete disruption of the nucleus (e.g., C/1999 S4 LINEAR) to separation of major fragments (e.g., 73P/Schwassmann—Wachmann 3) and spill-offs of smaller boulders (e.g., C/2001 A2 LINEAR). Fragmentation of comets produces secondary products over a wide range of sizes (from cometesimals to sub-micron dust). It is detectable through the presence of fragments (with own comae and tails) in the coma of the parent nucleus, through outbursts in its activity and through arc-lets (“coma wings”) associated with fragments. The secondaries have different lifetimes and show different non-gravitational forces. Nucleus splitting is also considered to generate whole families of comets (Kreutz group) or — if gravitational bound — multiple nuclei (e.g., C/1995 O1 Hale—Bopp). It may explain the striae phenomena seen in dust tails of bright comets (C 1995 O1 Hale—Bopp) and the detection of chains of impact craters on other bodies in the solar system. As process of significant mass loss it is relevant for the scenario of nucleus extinction, at the same time it also plays a role for the number statistics of existing (observable) comets and for the size distribution of comet nuclei. Various model scenarios for nucleus splitting are proposed: tidal disruption, rotational splitting, break-up due to internal gas pressure, fragmentation due to collision with other bodies. Only in one case, Comet D/1993 F1 Shoemaker—Levy 9, the physical process of fragmentation could be undoubtedly identified. In any case, comet splitting provides important insights in the internal structure, surface layering and chemistry of comet nuclei.