Origin, evolution and structure of the giant planets

Jupiter and Saturn are adiabatic spheres of hydrogen and helium, with central concentrations of heavier elements of the order of 10 Earth masses. Uranus and Neptune are ice-rich by comparison and have masses comparable to the cores of Jupiter and Saturn. It is argued that these planets started out substantially hotter than at present and have since been gradually cooling. It is also argued that the high-density cores of Jupiter and Saturn are primordial and might be the nuclei that promoted gaseous accretion and led to the current large masses of these planets. In this review, emphasis is placed on the basic ideas needed to construct static and evolving models, and an assessment is made of the relationship between these models and current ideas for the formation and evolution of the solar system