New interior models for Jupiter and Saturn are described that do not assume the temperature profiles to be adiabatic throughout the entire hydrogen-helium envelope. These models include the recently calculated radiative opacities due to hydrogen, helium, water, methane, and ammonia and an up-to-date hydrogen/helium equation of state. The helium abundance in the planet, the mass of the core, and the discontinuity of helium abundance at the molecular/metallic hydrogen phase transition (or the ice fraction in the core) are optimized to reproduce the observed mass, radius, and gravitational moments within their error bars.
These nonadiabatic models are characterized by the presence of a radiative zone in the outermost layers of the planet, surrounded by two convective zones. This radiative window yields a substantial modification of the thermal properties of the planets and leads to cooler interior models. The mass of Jupiter core is found to be slightly larger than for the adiabatic models. Finally, the mass fractions of heavy elements deduced from our calculations are in better agreement with the values inferred from atmospheric measurements. 1994 Academic Press, inc.