Saving planets with stochastic migration in dust-laden discs

Migrating Low-Mass Planets in Inviscid Dusty Protoplanetary Discs, Hsieh, H.-F., Lin, M.-K. 2020, MNRAS, 497, 2425

Planets are born in protoplanetary discs. However, in gas-dominated discs, low-mass planets undergo rapid inwards migration and are lost to the central star. It is then difficult to explain the enormous population of exoplanets discovered so far. A key challenge in planet formation theory is, therefore, how to slow down the migrating planets or even reverse their migration directions, so that they could evolve into the planetary systems we observed.

In collaboration with Dr. Min-Kai Lin at the Academia Sinica Institute of Astronomy and Astrophysics, we study how low-mass planets migrate in dust-rich protoplanetary discs. We conducted a series of high-resolution, two-dimensional two-fluid hydrodynamic simulations using the FARGO3D code run on high-performance computing clusters hosted by NTHU, ASIAA, and NCHC.

We uncovered a new regime of stochastic migration applicable to discs with abundant large dust grains, as illustrated in the movie above. In this case, the planet starts off migrating inwards smoothly. But after 200 orbits, numerous dust vortices formed in the disc continuously scatter the planet, causing its migration become stochastic, effectively halt the initial inwards migration, and even reverse the migration direction.