Scattering of small bodies by planets: a potential origin for exozodiacal dust?

¹ Institute de Planétologie, Université Joseph Fourier, CNRS 414, Rue de la Piscine, Domaine Universitaire, BP 53, 38041 Grenoble Cedex 9, France
e-mail: bonsora@obs.ujf-grenoble.fr
² LESIA-Observatoire de Paris, CNRS, UPMC Univ. Paris 06, Univ. Paris-Diderot, France

Received: 12 July 2012
Accepted: 20 September 2012

Abstract

High levels of exozodiacal dust are observed around a growing number of main sequence stars. The origin of such dust is not clear, given that it has a short lifetime against both collisions and radiative forces. Even a collisional cascade with km-sized parent bodies, as suggested to explain outer debris discs, cannot survive sufficiently long. In this work we investigate whether the observed exozodiacal dust could originate from an outer planetesimal belt. We investigate the scattering processes in stable planetary systems to determine whether sufficient material could be scattered inwards in order to retain the exozodiacal dust at its currently observed levels. We use N-body simulations to investigate the efficiency of this scattering and its dependence on the architecture of the planetary system. The results of these simulations can be used to assess the ability of hypothetical chains of planets to produce exozodi in observed systems. We find that for older (>100 Myr) stars with exozodiacal dust, a massive, large radii (>20 AU) outer belt and a chain of tightly packed, low-mass planets would be required to retain the dust at its currently observed levels. This brings into question how many, if any, real systems possess such a contrived architecture and are therefore capable of scattering at sufficiently high rates to retain exozodi dust on long timescales.