David Cébron

Host institution: National Centre for Scientific Research (CNRS)

Laboratory: LJK

Call for Projects: Starting (PE1)

Project name: THEIA – Topographic effects in planetary fluid cores: application to the Earth-Moon system

Amount:  1.44 M€


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 dissipations 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. My 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. I propose to investigate topographic effects in planetary fluid cores by combining theory, numerics and experiments. Using the largest turntable worldwide, I will build an experiment to study the dissipation of turbulent flows in the presence of rotation, density variations and topography. Building upon my recent advances in applied mathematics, I will develop new numerical models keeping only the relevant topographic effects. Using efficient spectral methods, I will reach unprecedented parameters, closer to planetary ones. Developing scaling laws, I will assess how planetary core dissipations and magnetic fields are modified by topographic effects. Beyond the Earth-Moon system, my models will also apply to fluid layers of other bodies, such as the subsurface oceans of the Jupiter icy moons, studied by future spatial missions (JUICE, Europa Clipper). This project is especially timely as the liquid core of Mars is studied by the on-going spatial mission InSight.

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