Author: Harold F. Levison

Status: Invited review to in Completing the Inventory of the Solar System, eds. T. Rettig and G. Hahn.

Abstract: The current comet classification scheme is re-evaluated in terms of the most recent models of the origin and dynamical evolution of comets and is found to be wanting. After a review of the current theories of the origin of comets and of the results of recent numerical simulations, a new taxonomy is developed. The main division between comets is defined by the Tisserand parameter, T, which is a measure of the influence of Jupiter on the dynamics of the comets. Comets with T<2 are called `nearly-isotropic' comets because they have a fairly uniform inclination distribution. Comets with T>2 are designated as `ecliptic' comets because of their very flat inclination distribution. Long-term dynamical integrations by Levison & Duncan (1994) have shown that over 90% of comets with periods currently less than 200 years remain in one of these two classes throughout their dynamical lifetimes. These new classes are thus dynamically significant and probably reflect the origin of the comets they contain. These classes are further subdivided, as described below.

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