Trapping of Low-Mass Planets Outside the Truncated Inner Edges of Protoplanetary Discs

We investigate the migration of a low-mass ($\lesssim 10 M_\oplus$) planet near the inner edge of a protoplanetary disc using two-dimensional viscous hydrodynamics simulations. We employ an inner boundary condition representing the truncation of the disc at the stellar corotation radius. As described by Tsang (2011), wave reflection at the inner disc boundary modifies the Type I migration torque on the planet, allowing migration to be halted before the planet reaches the inner edge of the disc. For low-viscosity discs ($\alpha \lesssim 10^{-3}$), planets may be trapped with semi-major axes as large as $3-5$ times the inner disc radius. In general, planets are trapped closer to the inner edge as either the planet mass or the disc viscosity parameter $\alpha$ increases, and farther from the inner edge as the disc thickness is increased. This planet trapping mechanism may impact the formation and migration history of close-in compact multiplanet systems.