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P218The viscosity of Super-Earths and
implications for their magnetic field generation
Vlada Stamenković, Doris Breuer and Tilman SpohnJoint Planetary Interior Physics Research Group
of The University of Münster and the IPR DLR Berlin
PROBLEM:
• We want to model the thermal evolution of Super-Earths!– Processes: Plate tectonics, Magnetic fields, etc
• But have only thermal properties, especially viscosity, for small pressures.• Viscosity controls the thermal evolution of planets and depends on
temperature T and pressure P!
• PRESSURE IS EXTREMELY IMPORTANT FOR SUPER-EARTHS AND HAS BEEN IGNORED SO FAR!
( , ) exp effE P VP T
RT
P218
PROBLEM:
• We want to model the thermal evolution of Super-Earths!– Processes: Plate tectonics, Magnetic fields, etc
• But have only thermal properties, especially viscosity, for small pressures.• Viscosity controls the thermal evolution of planets and depends on
temperature T and pressure P!
• PRESSURE IS EXTREMELY IMPORTANT FOR SUPER-EARTHS AND HAS BEEN IGNORED SO FAR!
*
( , ) exp effE P VP T
RT
THEREFORE:We include pressure dependence!
& Implications for mantle convection and dynamos!
P218
RESULTS 1: Viscosity
• NOW WE GET:– Large mantle viscosities and increasing with depth (adiabate)
Old
New
P218
RESULTS 2: NO convection
• Due to the large viscosity we get:– Super-Earths are not fully convecting planets!
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NO CONVECTION
RESULTS 2: NO convection
• Due to the large viscosity we get: – Super-Earths are not fully convecting planets!
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NO CONVECTION
CONTRARY TO ALL OLDER MODELS,
WHERE FULL CONVECTION ASSUMED!
RESULTS 3: NO magnetic fields?
• High viscosity and Low-lid thermally insulate the core• There is not enough power Φ to drive the magnetic dynamo!
P218
0(8 10 )Gyrs
Earth Super-Earth
0
B
