Planet Formation in Radiatively Inefficient Protoplanetary Discs.

Abstract

I examine the effects on planetary system formation of radiatively inefficient disc models where positive corotation torques may counter the rapid inward migration of low-mass planets driven by Lindblad torques. I use N-body simulations coupled with algorithms to model the evolution of the gas disc, type I migration, gap formation and type II migration, planetary atmospheres that enhance the probability of planetesimal accretion by protoplanets, gas accretion on to forming planetary cores and gas disc dispersal. The inclusion of entropy and vorticity related corotation torques can lead to a net positive torque thus giving rise to outward migration of planets. This can allow larger planets to survive for a longer period of time, allowing some planets to accrete enough gas within the lifetime of the disc to undergo runaway gas accretion thus forming gas giant planets. I review the current status of extrasolar planet observations and the methods with which these observations are made, and provide a contextual review of the theory of planet formation. Using these models, I have successfully formed a number of gas giant planets with semi-major axes ranging from 0.1 AU up to 75 AU and masses from 100 Earth masses through to 700 Earth masses, as well as a large number of terrestrial sized planets. In later simulations, a large number of super-Earth, Neptune-mass and gas planets that are too small to be considered giants were formed also.