The near perfect axisymmetry of Saturn’s observed magnetic field is problematic because of Cowling’s Theorem. Dynamos don’t easily produce magnetic fields with perfect axisymmetry. One mechanism to overcome this issue for Saturn is to appeal to a stably-stratified layer surrounding Saturn’s dynamo region that can attenuate non-axisymmetric field components. This means that, although the field in the dynamo region has non-axisymmetric structure, we only see the axisymmetric part of it outside of the planet. The presence of such a stably-stratified layer also has implications for the time variation of the magnetic field: the observed axisymmetric components of the field can only change on the very long timescale associated with magnetic diffusion. This means we shouldn’t expect to see much change in the field from spacecraft observations, even if they are decades apart. Relevant papers by group members and collaborators include:
- Stanley, S. and Bloxham, J., “On the Secular Variation of Saturn’s Magnetic Field”, Phys. Earth Planet. Int. 250, 31-34 (2016).
- Stanley, S., A dynamo model for axisymmetrizing Saturn’s magnetic field, Geophys. Res. Lett. 37, L05201, doi:10.1029/2009GL041752 (2010).
- Stanley, S. and Mohammadi, A., Effects of an outer thin stably-stratified layer on planetary dynamos, Phys. Earth Planet. Int., 168, 179-190 (2008).