Investigating Uranus' formation through the D/H ratio

The formation mechanisms of the ice giants Uranus and Neptune, as well as the origin of their elemental and isotopic compositions, have been long-standing subjects of debate. Several puzzling observations have challenged our understanding of these planets' formation processes. Spectroscopic observations have revealed that both Uranus and Neptune are highly enriched in carbon and perhaps deficient in nitrogen, an elemental composition that deviates from predictions based on our current understanding of planet formation. Also, the ices from which Uranus and Neptune originally formed might have had deuterium-to-hydrogen (D/H) ratios lower than the predicted cometary value, a characteristic that has not been envisaged in any other planets in our solar system.

Resolving these puzzles is crucial for advancing our understanding of the formation mechanisms and evolutionary processes that shaped these enigmatic ice giants. One key piece of observational data that can shed light on this mystery is the measurement of the D/H ratio in Uranus, provided by the Herschel space telescope. This measurement is vital for understanding the current planetary composition of Uranus.

The aim of this study is to investigate whether the CO/H₂O ratio of Uranus, inferred from the D/H measurement, is consistent with the composition in the protosolar nebula during its evolution. To achieve this, the following approach has been employed:

• Interior Models. Using interior models and assuming a cometary D/H value in the primitive ices of Uranus, the contemporary D/H measurement from Herschel can be related to the bulk CO/H₂O ratio of Uranus.
• Protoplanetary Disk Evolution Model. A protoplanetary disk evolution model that includes solid and gaseous phases, as well as clathrates, has been utilized to simulate the evolution of the CO/H₂O ratio in the protosolar nebula over time.
• Comparison of Ratios. The preliminary results compare the inferred CO/H₂O ratio of Uranus with the local CO/H₂O ratio in the protosolar nebula at different epochs, providing insights into the local conditions present during the formation of Uranus.

By combining observational data, interior models, and protoplanetary disk simulations, this study aims to shed light on the connection between the composition of Uranus and the conditions in the PSN during the planet's formation process.