Models of Uranus' interior and magnetic field

Abstract

Our understanding of Uranus' interior structure comes from the results of theoretical models. In this chapter, we review the methods for computing such models. We discuss the various physical assumptions employed, and assess their strengths and weaknesses. The accretion theory of the formation of the planets is summarized and the implications for the structure and composition of Uranus are presented. We then discuss the results of the most recent modeling efforts. All of these essentially agree as to the form of the interior density profile, but disagree as to the composition of the material which gives rise to that profile. This is due to the fact that the composition of a mixture is not uniquely determined by its density. This point is elaborated on, in the light of constraints from atmospheric observations, and studies of the chemistry of the deep interior. The implications of these model results are examined for their bearing on three important questions. First, the anomalously low internal heat source of the planet compared to its insolation is discussed. Several characteristic heatflows are evaluated, and it is suggested that convection in stably stratified layers may be the most reasonable interpretation of Uranus' low heat flow. Second, the strongly tilted dipole of the magnetic field is discussed, and a possible explanation is presented. Finally, the chemistry of Uranus' atmosphere and deep interior is reviewed in the context of these models, and the implications of these models for theories of the formation of Uranus are discussed.