# Rotational dynamics of planetary cores: instabilities driven by precession, libration and tides

## TL;DR

This paper investigates how gravitational interactions like precession, libration, and tides induce turbulent flows and instabilities in planetary cores, offering an alternative explanation for magnetic field generation beyond convection.

## Contribution

It introduces a new mechanism for dynamo action driven by tidally-induced instabilities, supported by recent nonlinear and dynamo simulation results.

## Key findings

- Instabilities can resonate inertial waves in planetary cores.
- Tidally-driven flows can sustain magnetic fields without convection.
- The mechanism explains the early Moon's magnetic field.

## Abstract

In this chapter, we explore how gravitational interactions drive turbulent flows inside planetary cores and provide an interesting alternative to convection to explain dynamo action and magnetic fields around terrestrial bodies. In the first section, we introduce tidal interactions and their effects on the shape and rotation of astrophysical bodies. A method is given to derive the primary response of liquid interiors to these tidally-driven perturbations. In the second section, we detail the stability of this primary response and demonstrate that it is able to drive resonance of inertial waves. As the instability mechanism is introduced, we draw an analogy with the parametric amplification of a pendulum whose length is periodically varied. Lastly, we present recent results regarding this instability, in particular its non-linear saturation and its ability to drive dynamo action. We present how it has proved helpful to explain the magnetic field of the early Moon.