Towards realistic models for the interior dynamics of Jupiter and Saturn

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The majority of numerical dynamo codes where developed with the geodynamo in mind. They neglect the compressibility of the dynamo medium and also assume that the dynamo region dynamically decouples from an overlying electrically insulating body – the rocky mantle in the case of Earth. Both assumptions are justified in the geodynamo context but not for the interior of the gas giants Jupiter and Saturn. Here, the density increases significantly with depth. Also, the dynamo region of these planets is not clearly decoupled from the overlying gas envelope since the increase in electrical conductivity with depth is gradual rather than abrupt. Another interesting feature, which has little been explore so far, is the helium precipitation thought to happen at least in Saturn’s outer layers. It may actually be responsible for the planets peculiar magnetic field. We plan to develop new numerical dynamo models that explore the effects of compressibility, of helium-rain, and of the coupling between the molecular gas envelope and the deeper dynamo region. The latter is one of the key questions for the Juno missions to Jupiter scheduled to be launched in 2011. Our simulations will not only support this mission but also provide realistic models for Saturn’s dynamo in time for the second extended Cassini mission.