An MHD-based model for wind-driven disc-planet interactions

Abstract: Hydrodynamic simulations of protoplanetary discs with planets typically assume that the disc is viscously driven, even though magnetic disc winds are now considered the primary driver of angular momentum transport through the disc. Magnetic disc winds are typically left out of hydrodynamic simulations because they require a magneto-hydrodynamic (MHD) treatment and an entire 3D domain, both of which are computationally expensive. Some studies have attempted to incorporate disc winds into disc-planet simulations without full MHD by adding a torque to mimic the effects of a disc wind. However, these studies predate any explicit 3D MHD simulations of planets in the presence of a disc wind. In light of recent MHD studies of disc winds beginning to include a planet, we develop a new disc wind prescription based on these studies and test its efficacy. With three main components, namely (i) excess torque in the planetary gap region, (ii) an MHD-based radial profile for the background torque, and (iii) a moderate level of viscosity, we find that we can essentially reproduce planetary gap profiles for planets above the thermal mass. With lower-mass planets, however, we find it more difficult to reproduce their gap structure. Lastly, we explore the planet's migration path and find that the planet rapidly migrates inwards due to the excess torque in the gap.