Rock-dominated Uranus and Neptune?

... Conversely, adopting a cometary D/H for the protoplanetary ices between (15-30)$\times10^{-5}$, we constrain the interior models of both planets to have an ice mass fraction of 14-32%, i.e. that the two planets are rock-dominated.

A possible solution to this unexpected result is that the interiors of Uranus and Neptune are actually dominated by rock. For icy material in the form of H2O and rocky material in the form of SiO2, an ice mass fraction of only 14-32 % is found. Still, a complete interpretation of the now accurate values of Uranus and Neptune D/H would greatly be aided by a more definite picture of their internal structures. The latter would benefit from improved gravity, shape and rotation data, that could be obtained from planetary orbiters.