PHYSICOCHEMICAL PROCESSES IN PLANETARY EVOLUTION

Data returned from exploration of the planets teach us that planets are highly individualistic despite the assumed underlying universality of the processes. It is argued that the diversity of evolutionary outcomes arises mainly because of the interplay of thermal and compositional effects, both in the assembly of planets and in their subsequent convective evolution. The role of compositional differences and phase transitions invalidates any view of planets that relies heavily on models consisting of a small number of homogeneous layers. Four illustrative examples of real planetary behaviour are discussed: sold-solid phase transitions in terrestrial mantles, volcanic styles and recycling in Venus, heat flows of the giant planets and the role of the Lorentz force in the dynamics of the non-metallic portions of giant planets.