Consistency tests of cosmogonic theories from models of Uranus and Neptune

The planetary ratios of ice to rock $\text{(}\text{I}\text{R}\text{)}$ abundances expected in Uranus and Neptune are derived on the basis of several cosmogonic theories. For both Uranus and Neptune the value of $\text{I}\text{R}$ lies between about 1.0 and 3.6. This value is difficult to reconcile with a scenario in which N and C are accreted primarily in the form of N₂ and CO. It is consistent with some versions of both giant protoplanet theories and equilibrium accretion theories.