So many dynamos: A study of planetary magnetic field morphologies

We present 3-dimensional numerical dynamo models for Uranus, Neptune and Mercury. These three planets possess magnetic field morphologies quite different from the axially-dipolar dominated fields of Earth, Jupiter, Saturn and Ganymede. Uranus' and Neptune's fields are non-dipolar and non-axisymmetric, and Mercury's field is much weaker in magnitude than expected for an Earth-like dynamo. We examine whether these differences in planetary magnetic field morphologies can be explained by differences in the planets' convective-region geometries. We implement geometries that are consistent with Uranus', Neptune's and Mercury's interior structures in numerical dynamo models and analyze the resulting fields.; For Uranus and Neptune, the implemented geometry consists of a thin convecting shell surrounding a stably-stratified fluid core. The magnetic fields produced can match the observed surface power spectra and eccentric dipole models for these planets. For Mercury, we implement a thin convecting shell surrounding a solid conducting inner core. For certain Rayleigh numbers, this geometry can produce weak surface magnetic fields that are still in the strong-field regime because the toroidal-poloidal field partitioning that results in these models is different from the Earth-like case. Our numerical models can produce toroidal-poloidal field partitioning similar to that inferred from observations of Mercury's field.; The relationship between convective-region geometry and the morphology of the produced magnetic fields shown here is important in the understanding of these planets' interiors and evolution and may also provide a valuable tool for studying planetary interiors through spacecraft magnetic observations.