Background
This project aims to show the world that SwRI’s mass spectrometry group is a leader in Uranian system science. The main benefit will be to make SwRI more competitive for upcoming instrument proposal opportunities on a Uranus orbiter and probe mission. This is the highest priority new NASA flagship mission that was recommended by the National Academy of Sciences to start in the next few years. We are establishing scientific expertise in this exciting new area on two fronts.
Approach
First, we have been developing new models for the bulk composition of the atmosphere of Uranus. These models are enabling us to provide novel interpretations of existing data (e.g., Voyager 2, ground-based), and to make predictions that can be tested by an atmospheric entry probe. We have found that the canonical solar abundances that serve as the basis of all past modeling require revisions to carbon and oxygen abundances, which have important implications for the nature of Uranus’s building blocks. In addition, we have developed algorithms that allow us to account for chemical reactions and isotopic mixtures that result when different reservoirs of primordial materials are mixed together. The latter capability is valuable as it highlights an important strength of our program: measuring isotopes using high-resolution mass spectrometry. The other emphasis of our work is to develop the first geochemical models for the compositions of oceans that may exist inside the large moons of Uranus. If these worlds have liquid water oceans, they might be habitable.
Accomplishments
We have developed a new thermodynamic database that includes minerals and aqueous species to understand what would happen if seafloor minerals were to interact with an ocean. The most significant aspect of our database is the inclusion of ammonium minerals. ammonia (and species derived from it) is thought to be one of the key volatiles in the outer solar system. Previous modeling was unable to realistically simulate its behavior in water-rock environments. We have used our new database to perform computations that predict the geochemical consequence of volatiles reacting with chondritic and cometary rocks under potential ocean conditions. We find that a large quantity of ammonia can be incorporated into altered rocks, and this process would expel significant amounts of sodium and potassium into the ocean. The implications are numerous and are still being studied, but they include the redistribution of heating in the interiors of ocean worlds, and the potential to sustain habitable conditions via radiolysis of ocean water. Our modeling also follows the fate of carbon dioxide, another key volatile that could be detected by a SwRI mass spectrometer on an orbiter at Uranus. Results from our work have been shared with the community, and we have received very positive feedback thus far.