Modeling the chemistry of planetary atmospheres: implications for the bulk compositions of giant planets
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The oxygen abundances of giant planets potentially constrain the conditions of the protoplanetary disk and formation models of planetary systems. In our solar system, the abundances of water, the primary carrier of oxygen in the atmospheres of giant planets, are still unknown for all four giant planets. Juno spacecraft, currently orbiting Jupiter, has the objective of constraining Jupiter's deep water abundance (at a few bars to a hundred bars level) through microwave radiometery. A Saturn entry probe is proposed as a candidate for the New Frontiers program, with the goal of making in-situ measurements of Saturn's atmospheric composition. However, it is not likely to reach deeply enough to directly measure the deep water abundance. There are no planned missions for the atmospheres of Uranus and Neptune. Disequilibrium species have long been used to constrain the deep water abundances for Jupiter and Saturn. In this dissertation, we aim to improve the chemical constraints on the deep water abundances.
For Jupiter, we improved the chemical constraints on the deep water abundance by CO. We proposed a new formulation for the deep eddy diffusion coefficient by analyzing the experimental studies of turbulent rotating convection. We considered two updated CO kinetic models, one model constrains the water enrichment (relative to solar) to be between 0.1 and 0.75, while the other constrains the water enrichment to be between 3 and 11. Our study quantitatively accounted for the uncertainties on the constraints due to different reaction rates. We also predicted that the abundances of disequilibrium species should have latitudinal variation due to the latitudinal dependence of the eddy diffusion coefficient. Such variations have been confirmed by VLA measurements \citep{Giles16}, however, the measured dependences are different from our predictions, which merits further investigations.
For Saturn, we proposed an approach to break the degeneracy between the deep water abundance and the deep eddy diffusion coefficient when interpreting the CO observations. We identified another disequilibrium species, C
The transit spectroscopy provided an opportunity for constraining the composition of extrasolar giant planets. JWST should be able to collect the highest quality transit spectra in the future. For extrasolar giant planet atmospheres we expect to measure and retrieve the abundance of the most abundant molecules, such as H
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Stacey, Gordon J
Desjardins, Olivier