Moment of Inertia Constraints from Layered Interior Models of Uranus and Neptune

This paper examines the moment of inertia factor of the ice giants as a test of interior layering. Using only published input values and transparent formulae, the calculation addresses whether a simple three-layer density model that reproduces each measured mean density also reproduces the published moment of inertia factor near 0.23, and how far it falls below the uniform-sphere value of 0.4. The headline results are: model_mean_density_kg_m3_uranus = 1272; model_mean_density_kg_m3_neptune = 1635; moment_of_inertia_factor_model_uranus = 0.246. 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 a three-layer model tuned only to mean density lands within a few hundredths of the published factor for both planets, showing that the moment of inertia mainly certifies the broad layering and cannot by itself distinguish among detailed composition profiles. Agreement and disagreement with independent published estimates are reported at their actual size, and the conclusions are limited to what the budget arithmetic supports.