Protostars and Planets VI, Heidelberg, July 15-20, 2013
Poster 2H029
Magnetic coupling in giant planet circumplanetary disks
Keith, Sarah L. (Macquarie University)
Wardle, Mark (Macquarie University)
Abstract:
During the final growth phase of giant planets, accretion is thought to be controlled by a surrounding
circumplanetary disk. Current accretion disk models rely on hydromagnetic turbulence (through the
magnetorotational instability) as the source of effective viscosity within the disk. However, whether the
circumplanetary disk is able to interact sufficiently with the magnetic field to produce this turbulence
remains a key uncertainty. Here, we examine the strength and nature of magnetic coupling in
circumplanetary disks to identify accreting regions. We model the disk as a standard alpha-disk
with a self-consistent opacity, and calculate the radial ionisation profile. We consider both turbulent
and large-scale vertical fields for driving accretion. By calculating the ohmic, hall and ambipolar
diffusivities, we find that the midplane is coupled out to only 30 Jupiter radii. Beyond this distance
thermal ionisation drops rapidly prohibiting coupling and accretion across the bulk of the disk. We
present an alternate model in which the entire midplane is thermally ionised, by allowing the viscosity
parameter, alpha, to vary radially. Although the entire disk is coupled and accreting, a high column
density is needed for the hot midplane (T ~ 1000K), such that the disk is self-gravitating at the outer
edge. We also discuss the effectiveness for cosmic ray surface ionisation and electric discharge as
additional ionising sources.
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