Invited speaker: Stable stratification in planetary interiors: constraints coming from the magnetic field

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• Thomas Gastine (Institut de Physique du Globe de Paris)
• Thursday 01 December 2022, 10:00-10:45
• Seminar Room 1, Newton Institute.

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DY2W03 - Modeling, observing and understanding flows and magnetic fields in the Earth's core and in the Sun

Convective motions which develop in the Earth liquid outer core or in the deep interior of the gas giants planets are thought to be the main driver of planetary magnetic fields via dynamo action. These electrically-conducting  fluid regions are nevertheless not necessarily entirely convecting. In the case of the Earth core, corroborating evidences coming from seismic studies, mineral physics and thermal evolution models suggest the existence of a stably-stratified layer underneath the core–mantle boundary. Such a layer could find its physical origination either in compositional stratification due to the accumulation of light elements at the top or the core or in thermal stratification due to the heat flux becoming locally sub-adiabatic. In the case of gas giant planets, constraints coming from gravity measurements, ab-initio calculations and ring-seismology (in the case of Saturn) suggest an intricate internal structure with fluid regions where helium would segregate from hydrogen, forming a compositionally-stratified layer. Such stable layers can have crucial dynamical impacts on dynamo action. Because of the inhibition of the convective motions, a stable layer is expected to primarily act as a low-pass filter on the magnetic field, smoothing out the rapidly-varying and small-scale features by skin effect. This defines a magnetic constraint on the properties of stably-stratified layers in planetary  interiors. During this talk, I will present global numerical dynamo models of the geodynamo and of the gas giants planets which incorporate stably-stratified layers to quantify their impact on the magnetic field generation. ~                                                                

This talk is part of the Isaac Newton Institute Seminar Series series.

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