Migrating low-mass planets in inviscid dusty protoplanetary discs, Hsieh, H.-F., Lin, M.-K., MNRAS, in press
Planets are born in protoplanetary disks. However, their survival is often threatened by rapid inwards migration and loss to the central star. It is then difficult to explain the enormous population of exoplanets discovered (more than 4200 as of this post). A key question in planet formation theory is, therefore, how to save planets or planetary cores so that they may evolve into the planetary systems we observe today.
In this new paper lead by Dr. He-Feng Hsieh at the Institute of Astronomy at National Tsing Hua University, we study how low-mass planets migrate in dust-rich protoplanetary disks, as opposed to the purely gaseous or nearly-dust free disks considered in previous works. There are several ways a protoplanetary disk can become enriched with dust, e.g. wind removal of gas and dust pile-ups so this is a natural limit to consider. We conducted a series of high-resolution, 2D numerical simulations using the FARGO3D code run on Graphics Processing Units (GPUs) on high-performance computing servers hosted by NTHU, ASIAA, and NCHC.
We uncovered a new regime of orbital migration applicable to disks loaded with large dust grains. In this case, planet migration becomes stochastic as illustrated in the movie above. The planet starts off migrating inwards smoothly, but around 200 orbits the disk begins to develop numerous dust vortices that continuously scatter the planet, causing its migration to become stochastic, effectively stopping the initial inwards migration, and even reverse it. These dust vortices likely originate from instabilities associated with thin dust rings around the gap opened by the planet (Huang et al., 2020) and have previously been observed in simulations with non-migrating planets (Yang & Zhu, 2020).
Our study shows that planets formed in dust-rich disks are less likely to be lost due to orbital migration.
Related works: Chen & Lin (2018), Pierens, Lin, and Raymond (2019).