DIX Planetary Science Seminar

Giant planets are known for their vivid and dynamic appearance. However, their beauty poses a challenge for measuring their bulk composition, as the optimal location representing the bulk metallicity is largely unknown – the key issue is turbulent mixing beneath their opaque clouds. I will show that the first-order estimation of this mixing can be constrained by balancing three processes: the hydrological cycle, the energy budget, and buoyancy forces characterized by the Richardson number. An active hydrological cycle transports heat from the deep reservoir to the cloud level through phase transition, known as the latent heat flux. This process limits the global mixing timescale to a few years on Jupiter and several decades on Saturn and Neptune. Then I will show that the nature of turbulent mixing on giant planets defies the simple dichotomy of stratified versus convective behavior. When radiative cooling weakens stratification, potential energy stored in the vertical wind shear can trigger large-scale storms as the Richardson number locally becomes supercritical due to the cooling of planets. Such instabilities manifest as periodic outbreaks near Jupiter's fastest eastward jet every four to five years and some giant storms on Saturn. These oscillations imply non-uniform chemical distributions and offer another approach to constrain the deep water abundance of giant planets.