On the interaction between embedded planets and the corotation region of protoplanetary discs

Abstract

Disc material in the corotation region librates with respect to low-mass planets on horseshoe trajectories. The exchange of angular momentum associated with this libration gives rise to the non-linear corotation torque (the horseshoe drag). For the first project described herein, we ran a suite of high-resolution 2D hydrodynamic simulations of low-mass (5 Earth mass) planets, at eccentricities 0 e < 0.3, embedded in both viscous protoplanetary discs with entropy relaxation and inviscid discs without. The attenuation of the corotation torque was obtained from these simulations and found to be well-fitted by an exponential decay with a characteristic ‘e-folding eccentricity’ that scales linearly with disc scale height. These results were tested with different disc scale heights between 0.03 and 0.1 and with a 10 Earth mass planet. In the second project in this thesis we sought to extend on these results by examining the case of an embedded 5 Earth mass planet in three dimensional discs. We found that our scaling relation held in this new case, confirming that it is possible to use 2D simulations with a softening parameter to capture the behaviour of the corotation torque. We investigated the time-averaged horseshoe width as a function of altitude and found that the corotation region extends from the midplane to around three scale heights, changing most near the midplane for eccentric planets. The final project looked at 3D radiative discs, under the influence of stellar irradiation, with more massive embedded planets capable of triggering gap formation. We use the pluto code to simulate a Jupiter mass planet at 5 AU in a protoplanetary disc. We describe our progress in understanding the process of gap formation in a case study of this class of hitherto undescribed disc.