The Effects of Nested Dynamos in the Gas Giants

Gravity measurements of the gas giants, as well as ring seismology in the case of Saturn, have led to increasingly complex structure models for both planets. The latest interior models for Jupiter and Saturn include a dilute, diffuse, or fuzzy core at their centres (e.g., Mankovich & Fuller 2021; Militzer et al. 2022). However, the dynamical nature of this central region and its effects on the dynamo process are not well constrained. Some hypothesise that the deep interior takes the form of a fully stably stratified dilute core while others argue for a convecting (inner) dilute core and a stably stratified transitional envelope atop. Either of these models will act to alter the geometry of the convective dynamo region considerably, especially in combination with likely additional stably stratified layers at mid-depths, due to helium rain.

Here we use 3D numerical MHD simulations to explore the effect of a dilute-core dynamo. As a first step, we adopt an imposed axial dipole with varying strength as a proxy for a deep dilute-core dynamo. We investigate its effects on the dynamical flows and magnetic field generation process in the convective metallic hydrogen layer above. In addition, a stably stratified transitional layer between the dilute-core dynamo and the convective metallic hydrogen layer has been implemented in our numerical models. 

With these numerical simulations, we aim to elucidate 1) which type of structures models leads to Jupiter-like or Saturn-like surface magnetic fields, and 2) if the deep dilute-core dynamo will leave observable imprints in the spatial or temporal pattern of the magnetic field.