Dynamical Simulations of the Planetary System HD 69830

Abstract

The planetary system of HD 69830 is uniquely constrained by observations of (i) an infrared excess indicative of a debris disk with warm dust and (ii) radial velocity variations indicative of three planets. This presents a valuable opportunity to test planet formation models by integrating dynamical models of planetary formation and migration with those for the sculpting of a dust-producing planetesimal disk. We perform n-body simulations and investigate the excitation of both planet and planetesimal eccentricities, the accretion of planetesimals onto the planets, and the clearing of a planetesimal disk by the planets as they grow in mass and migrate through the disk. In simulations tuned to closely follow previous semi-analytic models for the growth and migration of the planets, we find that the inner planet accretes significantly more planetesimals than previously estimated. We find that eccentricity excitation due to mutual planetary perturbations during and after the migration do not naturally produce the observed eccentricities. Our simulations suggest that this discrepancy may be reduced or possibly reconciled if the planets are significantly more massive than expected (possible if the planetary system's angular momentum were nearly parallel to our line of sight). Even if the planets are significantly more massive than previously assumed, we find that the migrating planets are inefficient at clearing the outer planetesimal disk and that a significant fraction of the planetesimal population beyond 1 AU remains bound on moderately eccentric and inclined orbits. While much of the remaining planetesimal belt would have eroded via a collisional cascade and radiation pressure, we explore whether some of the highly excited planetesimals may be able to persist over the age of the central star, producing the dust observed in the HD 69830 system.