Magnetically driven outflows from Jovian circum-planetary accretion disks

Abstract

We discuss the possibility to launch outflows from the close vicinity of a protoplanetary core considering a scenario where the protoplanet surrounded by a circum-planetary accretion disk is located in a circum-stellar disk. For the circum-planetary disk accretion rate we assume 6x10^{-5} M_jup/yr, implying peak disk temperatures of about 2000K. The estimated disk ionization degree and Reynolds number allow for a sufficient coupling between the disk matter and the magnetic field. We find that the surface magnetic field strength of the protoplanet is probably not more than 10 G, indicating that the global planetary magnetosphere is dominated by the circum-planetary disk magnetic field below 50 G. The estimated field strength and mass flow rates allow for asymptotic outflow velocities of 60 km/s. The overall outflow geometry will resemble a hollow tube or cone perpendicular the disk. Outflows from circum-planetary disks may be visible in shock excited emission lines along a tube of diameter of the orbital radius and thickness of about 100 protoplanetary radii. Energetically, protoplanetary outflows cannot survive the interaction with a protostellar outflow. Due to the efficient angular momentum removal by the outflow, we expect the protoplanetary outflow to influence the early planet angular momentum evolution.