THE ROLE OF THE MOLECULAR-METALLIC TRANSITION OF HYDROGEN IN THE EVOLUTION OF JUPITER, SATURN, AND BROWN DWARFS

An equation of state for hydrogen which predicts a molecular-metallic phase transition at finite temperatures has become available recently. A companion paper addresses the issue of the internal structures of Jupiter and Saturn, as derived with this new equation of state. Here we study the effect of this phase transition on the cooling histories of these two giant planets and of substellar brown dwarfs. The phase transition alters the present age of Jupiter and of Saturn by a few percent. Interestingly, the cooling of brown dwarfs is most strongly affected at the time when the interior adiabat crosses the critical point of the phase transition.