MONTE-CARLO INTERIOR MODELS FOR URANUS AND NEPTUNE

To explore a greater realm of model phase space than has previously be en mapped we generate randomly chosen interior models for Uranus and N eptune. The models are constrained by the observed mass, rotation rate , radius, and gravitational moments of the two planets. New models wit h a composition gradient in the outer third of the planetary radius ar e found for both planets. Such composition gradients may play a signif icant role in controlling the internal heat now. In agreement with pre vious models, we find that the pressure-density relation for the centr al third of both planets is consistent with either ice or a mixture of materials with a similar equation of state. While the range of allowe d models is now somewhat greater, the principal conclusions drawn from traditional interior modeling techniques are robust.