Planetesimal Dynamics in the Presence of a Giant Planet
Authors: Kangrou Guo, Eiichiro Kokubo
Standard models of planet formation explains 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 about 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. When the orbits of two objects are aligned, they encounter on tangential trajectories with low relative velocities, which lead to a higher chance of accumulation. The typical velocity dispersion for identical-mass planetesimals is of the order 10 m 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.
Link to the paper (arXiv): https://arxiv.org/abs/2106.06240
Figure 1: Schematic illustration of alignment of orbits. The dashed curves indicate parts of the orbits that are below the reference plane (yellow). (a): non-aligned orbits, m1 and m2 encounter with high relative velocity. (b): aligned orbits, m1 and m2 encounter on almost tangential orbits and with low relative velocity. This figure shows that even when two particles are on eccentric and inclined orbits, they can encounter with a low relative velocity when their orbits are well-aligned.
Figure 9 (b): Color maps of relative velocities at about 0.5 million years near 12 au. The relative velocity increases with increasing mass ratio. The typical relative velocity of identical-mass particles is on the order of 10 m/s.
Figure 10: Comparison of growth timescales in the aligned case (yellow) and non-aligned case (red) at different orbital distances. When the orbits are aligned, the growth timescale is significantly shorter – the growth of another planetary core outside the giant planet perturber can be accelerated under the coupling effect of secular perturbation and nebula gas drag.
Contact: Kangrou Guo (carol.kwok@grad.nao.ac.jp)
