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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