Details of the interior models of Uranus and Neptune. Top: illustration of the three-layer internal structure model assumed. Both the envelope and mantle contain hydrogen, helium, ices, and rocks, with the mantle expected to have a higher concentration of ices and rocks. The core is composed entirely of rocks. Bottom: envelope metallicity versus mantle metallicity for interior models of Uranus and Neptune. Each dot represents a model that fits both the gravitational data and radius of the respective planet. The color scale indicates the core mass.