Bulk Ice Mass Fraction of Uranus and Neptune from Specific-Volume Mixing

This paper examines the bulk ice content of the ice giants, estimated from density mixing alone. Using only published input values and transparent formulae, the calculation addresses what mass fraction of condensed volatile material, loosely called ice, is required for a two-component mixture of compressed ice and hydrogen-helium gas to match each measured mean density. The headline results are: ice_mass_fraction_uranus = 0.624; ice_mass_fraction_neptune = 0.762; ice_mass_kg_uranus = 5.417e+25. The method, inputs and limitations are stated in full so that any reader can reproduce or rescale every number from the deposited calculation script. The central finding is that the mixing estimate assigns roughly three fifths of Uranus and three quarters of Neptune to ices and rock, so the name ice giant is a statement about mass inventory, not about surface appearance. Agreement and disagreement with independent published estimates are reported at their actual size, and the conclusions are limited to what the budget arithmetic supports.