![]() ![]() In addition, we demonstrate torque and migration reversals induced by mid-plane magnetic stresses, with a bifurcation dependent on the disc surface density. ![]() In two regimes, the migration is approximately locked to the inward or outward radial gas flow, and in the other regimes the planet undergoes outward runaway migration that eventually settles to fast steady migration. Using simulations of laminar torqued discs containing migrating planets, we demonstrate the existence of the four distinct migration regimes predicted in Paper I. As shown in Paper I, a dynamical corotation torque arises due to the flow-induced asymmetric distortion of the corotation region and the evolving vortensity contrast between the librating horseshoe material and background disc flow. We examine the migration of low-mass planets in laminar protoplanetary discs, threaded by large-scale magnetic fields in the dead zone that drive radial gas flows. Flow-locked and runaway migration, and a torque prescription Low-mass planet migration in magnetically torqued dead zones - II. Finally, we use the simulation results to develop torque prescriptions for inclusion in population synthesis models of planet formation. We also develop an analytical model for the corotation torque at late times that includes viscosity, for application to discs that sustain modest turbulence. We develop a model for fast migration, and show why the outward runaway saturates to a steady speed, and examine phenomenologically its termination due to changing local disc conditions. In addition, we demonstrate torque and migration reversals induced by midplane magnetic stresses, with a bifurcation dependent on the disc surface density. We examine the migration of low mass planets in laminar protoplanetary discs, threaded by large scale magnetic fields in the dead zone that drive radial gas flows. Low mass planet migration in magnetically torqued dead zones - II. Furthermore, the magnetic field induced corotation torque and the dynamical corotation torque in a low viscosity disc can be regarded as one unified effect. Our results show that the corotation torque due to a laminar Hall-induced magnetic field in a dead zone behaves quite differently from that studied previously for a viscous disc. In this paper, we treat this effect by applying a symmetry argument to the previously studied case of a migrating planet in an inviscid disc. Hence, if the gas is torqued by a large-scale magnetic field so that it undergoes a net inflow or outflow past the planet, driving evolution of the vortensity and inducing asymmetry of the corotation region, the corotation torque can grow, leading to a positive torque. If there is relative radial motion between the disc gas and the planet, the librating streamlines will no longer be symmetrical. However, in such a low viscosity situation, the material on librating streamlines essentially preserves its vortensity. The corotation torque in an inviscid, isothermal, dead zone ought to saturate, with the libration region becoming both symmetrical and of a uniform vortensity, leading to fast inward migration driven by the Lindblad torques alone. Motivated by models suggesting that the inner planet forming regions of protoplanetary discs are predominantly lacking in viscosity-inducing turbulence, and are possibly threaded by Hall-effect generated large-scale horizontal magnetic fields, we examine the dynamics of the corotation region of a low-mass planet in such an environment. Paardekooper, Sijme-Jan Gressel, Oliver Lyra, Wladimir ![]() Low mass planet migration in magnetically torqued dead zones - I. ![]()
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