2020-7-22

Planetesimal dynamics in the presence of a giant planet

Speaker: Carol Kwok (Univ. of Tokyo, *Student talk)

Abstract:

The standard models of planet formation describe how planets form in axisymmetric, unperturbed disks in single star systems. When there is a massive companion perturbing the disk while planetary bodies start to form, however, the story might alter. For example, it is possible that giant planets could have already formed when other planetary embryos start to grow. In this case, the early evolution of planetesimals can be affected by strong perturbations from the massive planets in the system, and thus deviate from the standard scenario. Using N-body simulations, we investigate the dynamics of planetesimals, including the distribution and evolution of their orbital elements, in a system with the presence of nebular gas and a giant planet perturber at 5.2 AU. We aim at finding out the impact of the perturber on the formation of giant planet cores exterior to the orbit of the perturber. While confirming the results from Kortenkamp and Wetherill (2000), who studied the effect of the perturbation on the orbits of planetesimals interior to the perturber, we find that the orbits of particles distributed in ∼ 9 − 15 AU, except for the MMR locations, are generally aligned, and the typical velocity dispersions of identical-mass particles are on the order of ∼ 10 m/s in this disk region. As a follow-up of our previous work on the same topic, we narrowed the mass range of particles in order to minimize the effect of self-gravity of planetesimals. Meanwhile, we performed the simulations on a much longer timescale to cover the effect of gas drag on particles with larger masses. With long enough time (t >~ tau_gas), the particles of neighboring mass on the larger end on the mass spectrum become better aligned, resulting in lower encounter velocities among them. Within a reasonable degree of approximation and uncertainty, our results show that the dynamical features of planetesimals displayed in certain parts of the disk makes them ”accretion-friendly” regions where planetary growth is accelerated.