For two decades now, 3D computer simulations have been used to study how magnetic fields are generated by convection in the deep interiors of stars and planets. Models of the geodynamo have become particularly popular in recent years. They have produced dipole dominated fields outside the core and westward drift of the non-dipolar field, similar to that observed on the Earth’s surface. Many of these models show an eastward rotation of the solid inner core relative to the surface as inferred from some seismic analyses. Some models also occasionally produce spontaneous dipole reversals on a time scale not unlike that

seen for the paleomagnetic record. These results from magnetohydrodynamic (MHD) simulations have given some people the impression that the “geodynamo problem” is solved.