ERC project THEIA

• Title: Topographic effects in planetary fluid cores: application to the Earth–Moon system
• Period: 1 September 2020 – 31 August 2026 (completed)
• Overall budget: €1,448,493
• Principal investigator: David Cébron
• Funding: European Research Council Starting Grant, Horizon 2020, agreement 847433; CORDIS project record

Why topography?

Planetary cores are often modelled as fluids inside perfect spheres. Their boundaries are not perfectly smooth or spherical, however, and the resulting topography can change flows, dissipation and the torque on the surrounding mantle. THEIA studied these effects, with particular attention to the Earth and Moon and to their rotational and magnetic histories.

Theory, simulations and experiments

We combined local models of core–mantle coupling with studies of waves and flows in rotating, non-spherical interiors. The publications include work led by Rémy Monville on topographic drag, Vadim Giraud on inertial-wave drag, Paul Pružina on semiconvective dynamos and Paolo Personnettaz on inner-core damping. The numerics page links to the tools developed by team members and collaborators.

The one-metre THEIA apparatus was commissioned during the project and reached about 10 rpm. Initial spin-up experiments over flat and rough bottom topographies were performed in 2026. Their analysis was ongoing at the end of the grant; the experiments page describes the setup.

We are continuing to investigate how topography, stratification, waves and turbulence combine in boundary coupling, and how flows in non-spherical planetary cores relate to observations of rotation and magnetic fields.