The magnetic fields of giant planets could result from the self-organization of an initially stable atmosphere

Giant planets such as Jupiter and Saturn are primarily composed of heavier hydrogen, with a smaller fraction of helium. Helium tends to sink, creating stable layers. A competing effect comes from temperature, which is higher in the interior, but this is not sufficient to overcome the stability of the helium profile and allow convective motions. However, due to the physical properties of the mixture, weak motions can appear through a process called double-diffusive convection (also observed in polar oceans, where salt plays the role of helium).

These new simulations show that these weak double-diffusive motions can then self-organize into two layers : an inner convective layer, with velocities sufficient to generate a complex magnetic field, and an outer stable layer. In the latter, large-scale winds, guided by rotation, shape the magnetic field into a simple dipole, similar to that of giant planets.

These results suggest how initially stable fluid layers could self-organize to generate the magnetic fields of giant planets, and more broadly, those of exoplanets or stellar interiors.