Effects of the Planetary Field on the Accretion Process of a Planet in the Final Stage of Giant Planet Formation

Abstract

Recent studies suggest that the magnetic field may play an important role in the formation of giant planets during the final stage of the formation process. In this paper, we construct a circumplanetary system around a planet that is in the final formation stage to investigate the effects of the planetary magnetic field on the accretion process of the planet at this stage. We find that at the early times of our magneto-hydrodynamic (MHD) simulation, the magnetic loops connecting the planet and the circumplanetary material inflate upward due to the build-up of the toroidal field pressure with magnetic islands forming inside the loops, which changes the flow pattern above the planet in comparison with the hydrodynamic case. We find that a low-density gap, which is produced by the strong magnetic pressure, appears along the disk’s surface and expands as the system evolves. Accompanied by the accretion flow above the disk surface, the disk surface field lines can reconnect with the magnetic loops anchored on the planet. Thus, the material above the disk’s surface can permeate into the loops anchored on the planet via reconnection and can be accreted to the planet through the loops. Comparing the results in the hydrodynamic and MHD simulations, we find that the mass accretion rate and the angular momentum transport rate from the infalling gas to the planet do not change apparently when the effects of the magnetic field are included, but these rates from the circumplanetary disk to the planet increase significantly by an order of magnitude.