Planetesimal Dynamics in the Presence of a Giant Planet

Abstract: Standard models of planet formation explain how planets form in axisymmetric, unperturbed disks in single star systems. However, it is possible that giant planets could have already formed when other planetary embryos start to grow. We investigate the dynamics of planetesimals under the perturbation of a giant planet in a gaseous disk. Our aim is to understand the effect of the planet's perturbation on the formation of giant planet cores outside the orbit of the planet. We calculate the orbital evolution of planetesimals ranging from $10^{13}$ to $10^{20}$g, with a Jupiter-mass planet located at 5.2 au. We find orbital alignment of planetesimals distributed in $\simeq 9$-15 au, except for the mean motion resonance (MMR) locations. The degree of alignment increases with increasing distance from the planet and decreasing planetesimal mass. Aligned orbits lead to low encounter velocity and thus faster growth. The typical velocity dispersion for identical-mass planetesimals is $\sim \mathcal{O}(10)$ $\rm{m\text{ } s}^{-1}$ except for the MMR locations. The relative velocity decreases with increasing distance from the planet and decreasing mass ratio of planetesimals. When the eccentricity vectors of planetesimals reach equilibrium under the gas drag and secular perturbation, the relative velocity becomes lower when the masses of two planetesimals are both on the larger end of the mass spectrum. Our results show that with a giant planet embedded in the disk, the growth of another planetary core outside the planet orbit might be accelerated in certain locations.