Modeling Volatile Outgassing in Rocky Exoplanets: Coupling Interiors and Atmospheres in the JWST Era

Mridha, Sudipta (2025) Modeling Volatile Outgassing in Rocky Exoplanets: Coupling Interiors and Atmospheres in the JWST Era. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Sudipta Mridha (20MS221)) 20MS221_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (2MB)

Abstract

The Magma Degassing Model is used to determine the atmospheric composition of an exoplanet through the outgassed atmosphere. The model is based on coupling the interior of the planet with the atmosphere, using the melt-gas and gas-gas interaction. It calculates the gas speciation for the C − O − H − S − N gas system in equilibrium with the silicate melt at the surface of a planet in a given pressure, temperature, and melt oxygen fugacity (fO2 ), considering both homogeneous gas-gas equilibria and gas-melt heterogeneously gasmetal symbiosis. The Gibbs free energy of each species is used along with the equilibrium constant to calculate the fugacity of each of the gases in the C − O − H − S − N gas system, including gases such as H2O, O2, H2, CO, CO2, CH4, S2, SO2, H2S, and N2. For the ascent of magma from the mantle to the surface, the pressure decreases, and due to that, the gases that were dissolved in the melt at high pressure are released. We determine the amount of gases released with the ascent of the magma. The mass balance method is used to calculate the final composition and speciation of the atmosphere through outgassing. We have compared our results with an already existing degassing code, EVo, which uses the total abundance of C,O,H, S, and N in the system, i.e., the mantle. Our results perfectly overlap with the results from EVo on a log scale, instead of using the mass balance equation and the oxide composition of the melt to determine the atmospheric composition. We have explored the change in the outgassed amount with the ascent of melt, change in outgassing for two different types of melt ( Basalt and Phonolite) and the change in outgassed amount for melt with different oxygen fugacity.

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