MAGNETIC-FIELD GENERATION IMPEDED BY INNE R CORES OF PLANETS

Influence of an inner core on inviscid solutions of an alpha omega geo dynamo model is studied. Previous studies missed these solutions becau se symmetry about the equatorial plane was assumed. Flow across the eq uatorial plane vanishes indeed when symmetry is imposed and is shown h ere to be a crucial ingredient of inviscid solutions. A solid inner co re sets a barrier to such a flow. As a consequence, when the radius b of the inner core is an important fraction of the radius a of the oute r core (b/a > 0.35), dynamo action is strongly impeded and strong-fiel d solutions, which have the greatest geophysical relevance, are prohib ited.