Interior Structure and Dynamics of the Ice Giants

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The ice giants Uranus and Neptune offer several interesting puzzles. Their magnetic fields differ from those of any other planet since they are not dominated by a dipole component and have a very complex structure without any obvious symmetry. Moreover, though the ice giants are far away from the sun their atmospheric winds are the fastest in the solar system. Another puzzle is the fact that Uranus’ luminosity is too low. All these features offer clues about the special interior structure and dynamics of these planets that must be interpreted based on scientific models. To become more useful, however, these models need to be refined. We plan to concentrate on models concerning the interior dynamic and magnetic field generation in this proposal. Six different options have been suggested to explain why the magnetic fields of Uranus and Neptune are not dipole-dominated. For example, the density stratification or the radial variations in electrical conductivity are two possible reasons. Several of the suggested alternatives originated in our group and we have the numerical means to study all of them further in order to explore their potential. To better constrain the dynamical models we will collaborate with the group around Prof. Ronald Redmer in Rostock and around Prof. Richard Holme in Liverpool. The Rostock group will provide models of the interiors structure and material properties; Prof. Richard Holme has the expertise necessary to test the simulated magnetic fields against the original Voyager data. Having six different scenarios to obtain non dipole-dominated fields doesn’t necessarily mean that all these fields are Uranus or Neptune-like. The ultimate goal is to construct a model that is compliant with our knowledge of the interior structure, of the magnetic fields and ideally also with the observed surface winds. The latter point touches on the question how these fierce winds are driven and how deep they reach into the planet.