Uranus Revealed: What its D/H Ratio Tells Us About its Formation

Uranus and Neptune are among the least studied bodies in our Solar System, and their composition and formation processes remain subjects of ongoing debate. Observations of these icy giants have shown that both planets are significantly enriched in carbon and moderately enriched in nitrogen relative to protosolar values, challenging current planet formation models. Additionally, measurements of the deuterium to hydrogen (D/H) ratio, obtained by the Herschel Space Telescope, reveal a supersolar value, although lower than that of comets. This D/H ratio provides valuable insights into the bulk composition of Uranus, offering clues to its formation conditions.

The goal of this study is to determine whether the CO/H2O ratio of Uranus, derived from its D/H measurement, is consistent with the composition of the protosolar nebula (PSN) during its evolution. To achieve this, we use an interior model of Uranus, assuming the planet is composed entirely of ice. From this model, we derive the CO/H2O ratio of Uranus based on its D/H ratio, with the assumption that the D/H ratio in its original ices mirrors that of comets. We then compare this CO/H2O ratio to the corresponding ratio in the PSN, using a protoplanetary disk model that accounts for the evolution of species in multiple phases, including clathrate hydrates.

Our preliminary results compare the CO/H2O ratio derived from Uranus' D/H ratio with the local CO/H2O ratio in the protosolar nebula at different epochs, providing insight into the conditions that existed during Uranus' formation. Exploration of different interior models, including variations in the ice/rock ratio within Uranus, can lead to variations in the bulk CO/H2O ratio of the planet. Therefore, our study also investigates the relationship between Uranus' ice/rock ratio and its formation conditions.

By combining observational data, interior models, and protoplanetary disk simulations, this work seeks to elucidate the link between Uranus' composition and the conditions of the PSN during the planet's formation.