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The scattering of small bodies in planetary systems: constraints on the possible orbits of cometary material




The scattering of small bodies by planets is an important dynamical process in planetary systems. In this paper, we present an analytical model to describe this process using the simplifying assumption that each particle’s dynamics are dominated by a single planet at a time. As such the scattering process can be considered as a series of three-body problems during each of which the Tisserand parameter with respect to the relevant planet is conserved. This constrains the orbital parameter space into which a particle can be scattered. Such arguments have previously been applied to the process by which comets are scattered to the inner Solar system from the Kuiper belt. Our analysis generalizes this for an arbitrary planetary system. For particles scattered from an outer belt directly along a chain of planets, based on the initial value of the Tisserand parameter, we find that it is possible to (i) determine which planets can eject the particles from the system; (ii) define a minimum stellar distance to which particles can be scattered; and (iii) constrain a range of particle inclinations (and hence the disc height) at different distances. Applying this to the Solar system, we determine that the planets are close to optimally separated for scattering particles between them. Concerning warm dust found around stars that also have Kuiper belt analogues, we show that, if there is to be a dynamical link between the outer and inner regions, then certain architectures for the intervening planetary system are incapable of producing the observations. We speculate that the diversity in observed levels of warm dust may reflect the diversity of planetary system architectures. Furthermore, we show that for certain planetary systems, comets can be scattered from an outer belt, or with fewer constraints, from an Oort cloud analogue, on to star-grazing orbits, in support of a planetary origin to the metal pollution and dustiness of some nearby white dwarfs. In order to make more concrete conclusions regarding scattering processes in such systems, it is necessary to consider not only the orbits available to scattered particles, but also the probability that such particles are scattered on to the different possible orbits.