Libration-driven flow in planetary cores and subsurface oceans.

In the present study, we investigate the flow driven by longitudinal libration in the liquid layer of planetary bodies via a coupled experimental-numerical approach. Extending the work of [7], we consider the case of a non-axisymmetric container to account for the topographic coupling between the fluid and the solid shell that arises naturally in planets in low order spin-orbit resonance such as Mercury, Io, Titan, Europa, the Earth’s moon or Ganymede. We show that depending on the libration frequency, laminar or turbulent flows can develop in the system as the result of growth and collapse of an elliptical instability. An analytical expression of the growth rate of the instability is obtained using a WKB analysis further validated by series of numerical simulations. Extrapolation of our findings to planetary conditions suggest that some librating planets may be subject to elliptical instabilities, therefore to turbulence in the liquid layer leading to significant energy dissipation [5].