Magnetic Turbulence in Giant Planet Formation
Sarah Keith
Magnetic Fields Workshop 2012
Accretion onto Giant Planets
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•Planets grow through accretion
•Accretion requires viscosity
•Viscosity from magnetic turbulence is currently the only viable source
•Magnetic turbulence requires a
magnetic field – disk coupling
Does magnetic turbulence occur?
Do circumplanetary disks couple to magnetic fields?
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Outline
Model Disk Temperature, Density
Degree of Ionisation
Magnetic Field
Magnetic Diffusivity
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Disk model
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Calculating disk profiles
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Opacity Law
We solve for the opacity using the measured Bell & Lin 1994 opacity
law
Ice Grains Metal Grains
Molecules
H-Scattering
Bound-free & free-free
Electron Scattering
Be
ll &
Lin
19
94
Disk Profiles
Midplane Temperature
Scale Height
Surface Density
Opacity
Temperature Profile
Standard parameter set
Ionisation Fraction
SOURCE : Thermal ionisation
Potassium –low ionising potential
Hydrogen – abundant
SINK : Dust grains
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Ionisation Model
Hydrogen
Potassium
Dust grains
Magnetic Field
Magnetic Diffusivity
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Magnetic Diffusivity
Poorly coupled Well coupled
Ohmic
Hall Ambipolar
Coupling Threshold
Conclusions
The disk couples out to 40 Jupiter radii
but the rest of the disk is does not couple
No accretion across most of disk
- Other ionising sources?
- Accretion in layers above midplane?
- Viscosity prescription using MHD simulations?
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