Two- and three-layer models of Uranus

The authors present simple two-layer models of Uranus with rocky core and polytropic envelope satisfying exactly the observed mass, radius and the gravitational moments. The models show that the value of the fourth order zonal harmonic is J4 <approx. -38 X 10-6, while J6 approx. 10-6. More elaborate three-layer models fail to satisfy the observational constraints of the ice/rock ratio and/or of the rotation period. It is concluded that three-layer models with uniform chemical composition in each layer may be too restrictive. More realistic models should account for variable chemical composition within each layer. (Auth.)