Thinkshop 2020

Understanding the origins and dynamics of massive planets during the planet-formation process is essential to understanding how the structures of individual planetary systems came to be. Massive planets have the ability to open gaps in their host disk, and the radial movements of these gap-opening planets is typically referred to as type II migration. In the classical view, a protoplanetary disk accretes onto its star on a viscous timescale, carrying this gap inwards with the planet moving with the gap. This theory assumes that the planet remains in a state of quasi-equilibrium at the center of the gap. However, a non-zero torque from the disk must be applied to the planet for it to move radially, meaning the planet is not necessarily located at equilibrium. This implies that while the gap is in motion, and the planet is being dragged along with it, the location of the planet is not necessarily at the center of the gap. In addition, if we define the location of the gap center to be the radial position of a planet with a fixed orbit (i.e., a non-migrating planet), we also consider the possibility that the equilibrium position of the planet differs from this center. We explore these properties involving the gap-planet interaction of an evolving protoplanetary disk with 2D simulations using the FargOCA hydrodynamics code. We accomplish this by fixing the orbital radius of a massive planet ($M_p/M_* = 0.001$) until its disk has reached a steady state. At this stage we release the planet from its fixed orbit, and allow it to migrate freely. We then analyze the planet's displacement from equilibrium, as well as its displacement from the gap center, varying disk properties such as aspect ratio and viscosity, and explore their effects on the planet migration rate.