Dynamics in the interior of giant planets and ex-oplanets: the new revolution

Supervisors: Isabelle Baraffe and Thomas Guillet

Exquisite data recently obtained by the space missions Cassini and Juno provide new constraints on the interior structure of our Giant planets Jupiter and Saturn. These data have revolutionised the standard picture of homogeneously mixed planets. The structure of these giant planets appears to be much more complex than previously thought with a succession of convective regions separated by stably stratified layers with a gradient of chemical composition. Compositional gradients in the deep interior of these plaets may originate at very early stages of the planet formation process or may be due to the erosion of a solid core during the planet's evolution over billion of years. Combined with fast rotation, which characterises our giant planets (rotation rates of typically 10 hours), the presence of such gradients can generate instabilities known as double-diffusive instabilities and can significantly affect the efficiency of convective heat transport and chemical mixing. 

The general goal of this project is to analyse the impact of compositional gradients and rotation on the transport properties of convection. The first goal is to understand why Jupiter and Saturn are not fully mixed. The second goal is to determine the origin of the compositional gradients. These are two unsolved problems in the field. The study will be extended to giant exoplanets with different masses and rotation rates, in order to determine whether the inefficiency of mixing processes in giant planets of our Solar System is characteristic of giant exoplanets in other planetary systems.

The project will rely on sophisticated numerical simulations based on a fully compressible, time implicit hydrodynamical code MUSIC (MUlti-dimensional Stellar Implicit Code) developed by our team. We plan to explore realistic Jupiter/Saturn-like conditions based on the microphysics (equation of state, transport coefficients) appropriate for the description of giant planet interiors. This project will develop the very first multi-dimensional models of dynamical processes in realistic Jupiter and Saturn interiors.

This PhD project will allow the candidate to develop a solid understanding of the physics and fluid dynamics processes characterising the deep interior of giant planets. The candidate will also gain extended training in multi-dimensional numerical simulations, high-performance-computing and advanced data analysis techniques.