ERC project THEIA

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Abstract

Understanding planetary core flows is crucial as they generate planetary magnetic fields and modify planetary rotation. However, their study is an outstanding challenge involving geomagnetism, geodesy and fluid mechanics. Notably, present models fail to explain two puzzling observations. First, geodesy constrains the Earth and Moon core dissipation to values exceeding those of current theoretical models. Second, lunar paleomagnetism gives an early Moon magnetic field too intense for the current planetary dynamo paradigm, based on convection.

This project tackles these issues by going beyond the present planetary core simulations, performed in exact spheres. Planetary core boundaries are actually not spherical, being affected by large-scale and small-scale deformations. This topography, although advocated for a long time to play a role for the core dynamics, has been largely overlooked in core flow models.

We will this investigate topographic effects in planetary fluid cores by combining theory, simulations and experiments. We will build an experiment to study the dissipation of turbulent flows in the presence of rotation, density variations and topography. Building upon our recent advances in applied mathematics, we will develop new numerical models keeping only the relevant topographic effects. Using efficient spectral methods, we will reach unprecedented parameters, closer to planetary ones. Developing scaling laws, we will assess how planetary core dissipation and magnetic fields are modified by topographic effects. Beyond the Earth-Moon system, these models will also apply to fluid layers of other bodies, such as the subsurface oceans of the Jupiter icy moons.

Precession driven dynamo in spheroidal-like geometry
Preliminary XSHELLS simulation (grey colors for the flow, and magnetic lines)
David Cebron / ISTerre / OSUG