Gap Formation in Protoplanetary Discs

Abstract

In this thesis, we address a wide range of topics revolving around the interactions between a protoplanetary disc and a planet situated within. Initially, we present an overview of the background to protoplanetary disc physics. We then discuss our work, which is the body of this thesis and addresses three di erent problems that exist regarding planet-disc interactions. The rst of these problems is the signi cant di erence between the depth of gaps formed by planets in one dimensional and two dimensional numerical simulations. We investigate this by applying one dimensional gap forming potentials axisymmetrically across a two dimensional disc containing no planet and observe the results. We nd that the discrepancy between gap depths is reduced and the reason for this is the Rossby Wave Instability in two dimensions, which is not accounted for in one dimension. The second problem we address is that Type II planetary migration is too fast to explain the population of gas giant planets at larger orbital radii. Hence, we investigate a method which can slow down Type II migration, the heating of the outer edge of a giant planet gap by incident radiation from the central star. We nd this can reduce the net torque on the planet, potentially slowing or even reversing Type II migration. The third problem we investigate is more observational in nature. Almost any observed gap can have a planetary explanation if the viscosity of the disc and mass of the planet are unknown. Hence, we present a way to break this degeneracy, using the presence or absence of vortices to help constrain these parameters. We nd that often high mass planets can be ruled out in axisymmetric discs and that if discs are low viscosity, planets may not need to be particularly massive to form vortices.