Master thesis defense by Gretchen Schowalter
Modeling the Great Oxidation Event (GOE) with a Kinetic Equilibrium Model. Can we observe an oxidation event on exoplanets with synthetic transit radii?
Abstract
The Great Oxidation Event (GOE) occurred 2.54 billion years ago (Gya) and transformed the composition of the early Archean Earth’s atmosphere from being less than 1ppm of O2 to approximately 2% (Catling & Kasting, 2017).
We model the processes behind the GOE by using the complete photochemical network detailed in Liu et al.(2021a) with additional reactions describing the process of carbon burial made possible from oxygenic photosynthesis.
The main goal of this research is to see how processes similar to the GOE might be observable on exoplanets through transit spectroscopy. With this work we model with a kinetic equilibrium code, and create synthetic transit depth spectra at different points in the evolution using the petitRadtrans python package (Mollière et al., 2019).
Then, these synthetic transit radii can be created from the model data and compared to current observation using the PandExo exoplanet characterization toolkit (Batalha et al., 2017). By taking the outputs of the model at different time steps, there is a visible difference in the transit radii produced.
Our preliminary model results suggest that the most observable difference in the atmospheric composition is the decline in CO2 and CH4 caused by burial of carbon as organic material and consequently the creation of OH. We expand on these results by increasing the chemical network to include more of the processes affecting the atmospheric O2, in particular the ability to detect O2 via the proxy of O3.
We also compare two model scenarios: one with carbon burial and one without. These results suggest an increase in H2O and a decrease in CO in the scenario with carbon burial. Improving our understanding of O2 in the atmosphere might be a crucial next step in the search for complex life outside of Earth, both due to the role of O2 as a biosignature, and because complex life might be more dependent on high energy available in aerobic metabolism (Catling et al., 2005).
Supervisors
Thorsten Balduin, Nanna Bach-Møller, Uffe Gråe Jørgensen
External Censor
Hans Kjeldsen, Århus University
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