Magnetically driven outflows from Jovian circum-planetary accretion disks

Institut für Physik, Universität Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany 
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany

Corresponding author: cfendt@aip.de

Received: 1 August 2003
Accepted: 6 October 2003

Abstract

We discuss the possibility to launch an outflow from the close vicinity of a protoplanetary core considering a model 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 implying peak disk temperatures of about 2000 K. 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 of 50 G. The existence of a gap between circum-planetary disk and planet seems to be unlikely. The estimated field strength and mass flow rates allow for asymptotic outflow velocities of . The overall outflow geometry will be governed by the orbital radius, resembling a hollow tube or cone perpendicular the disk. The length of the outflow built up during one orbital period is about 100 AU, depending on the outflow velocity. 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. We derive particle densities of 3000  in this layer. 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. If this is true, planets which have produced an outflow in earlier times will rotate slower at later times. The mass evolution of the planet is, however, hardly affected as the outflow mass loss rate will be small compared to the mass accumulated by the protoplanetary core.