Science goals for the next generation of numerical dynamos

Over the past decade, numerical dynamos have dramatically advanced our understanding of the origin of the geomagnetic field and planetary magnetic fields, offering first-principles insight into magnetic field behavior on timescales ranging from years to billions of years. Nevertheless, all of the numerical dynamos presently in use are overly simplified in their treatment of the actual dynamics in planetary cores. In particular, the current generation of numerical dynamos use unrealistic values of critical transport properties such as viscosity and conductivity, as well as unrealistically slow rates of planetary rotation, making it necessary to extrapolate over many orders of magnitude before applying the results of numerical dynamos to planetary dynamos. The next generation of numerical dynamos aim to remove these limitations, making it possible to address a host of unresolved problems in planetary dynamics. A partial list of the most worthy problems for the next generation of numerical dynamos includes the effects of light elements, stratification, freezing, melting and high conductivity in terrestrial planet cores, couplings between the outer and inner core and the mantle, polarity reversal and excursions processes, torsional oscillations, magnetic field future-casting, core-mantle evolution, and comparisons between the geodynamo, laboratory dynamos, and dynamos in other planets. Two of the most significant goals for the next generation of numerical dynamos that merit special focus are (1) dynamo action with realistic physiochemical properties and realistic rotation rate, (2) and simulating the evolution of the core and its magnetic field over the planet's history.