9725627 Roberts The recent simulations of the geodynamo by Kuang and Bloxham, and earlier by Glatzmaier and the P.I., Roberts, have been in good agreement with the observed characteristics of the observed geomagnetic field, including polarity reversals. They have also provided new targets, as with the prediction by Glatzmaier and Roberts that the inner core should rotate eastwards relative to the mantle, which was subsequently supported by two independent seismological investigations. In this grant, the PI and collaborator Glatzmaier plan to add further realism to the model by reducing viscous diffusion and by including core turbulence, and to improve the numerical resolution and accuracy of the computational techniques. They shall also investigate the geodynamo in past geological epochs, and extend their studies to dynamos operating in Jupiter's Galilean satellites. ***