Monte Carlo interior models for Uranus and Neptune

To explore a greater realm of model phase space than has previously been mapped, randomly chosen interior models are generated for Uranus and Neptune. The models are constrained by the observed mass, rotation rate, radius, and gravitational moments of the two planets. New models with a composition gradient in the outer third of the planetary radius are found for both planets. Such composition gradients may play a significant role in controlling the internal heat flow. In agreement with previous models, it is found that the pressure-density relation for the central third of both planets is consistent with either ice or a mixture of materials with a similar equation of state. -from Authors