Interior Models of Uranus and Neptune

TL;DR

This paper develops empirical pressure-density models of Uranus and Neptune constrained by gravitational data and interprets them with physical equations of state, revealing similar compositions but different envelope characteristics.

Contribution

It introduces empirical interior models constrained by gravitational data and interprets them with physical equations of state, highlighting differences in planetary envelopes.

Findings

Uranus and Neptune have similar compositions with different envelope types.

Neptune requires a non-solar envelope, Uranus a solar one.

Gradual increase of heavy elements towards the centers is consistent with gravitational data.

Abstract

'Empirical' models (pressure vs. density) of Uranus and Neptune interiors constrained by the gravitational coefficients J_2, J_4, the planetary radii and masses, and Voyager solid-body rotation periods are presented. The empirical pressure-density profiles are then interpreted in terms of physical equations of state of hydrogen, helium, ice (H_2O), and rock (SiO_2) to test the physical plausibility of the models. The compositions of Uranus and Neptune are found to be similar with somewhat different distributions of the high-Z material. The big difference between the two planets is that Neptune requires a non-solar envelope while Uranus is best matched with a solar composition envelope. Our analysis suggests that the heavier elements in both Uranus' and Neptune's interior might increase gradually towards the planetary centers. Indeed it is possible to fit the gravitational moments without sharp compositional transitions.