Our inhomogeneous and unique outer planets

We present interior models of the outer planets in the solar system. We find that none of these planets can have a constant metallicity throughout the interior. For Uranus we find a significantly smaller outer envelope metallicity than for Neptune. The cooling time of Uranus can be brought into agreement with the age of the solar system if the deep interior is assumed to have a lower heat flux than along an adiabatic gradient. For Saturn, our models predict an atmospheric He/H mass fraction of 0.1, i.e. smaller than Jupiter’s.