Planetary and exoplanetary Astronomy Lunch Seminar (PALS) for 2022-09-12

Series: Planetary and exoplanetary Astronomy Lunch Seminar (PALS)
Date: Monday 12-September-2022
Time: 11:15-12:15
Location: ATL 1250
Speaker: Maggie Thompson
Title: Terrestrial Exoplanet Atmospheres: From Outgassing Origins to Likely Observable Biosignatures

Abstract: Exoplanet science is now focusing on characterizing exoplanet atmospheres, including those of terrestrial-class, potentially habitable planets. My PhD research at the University of California, Santa Cruz has centered on two themes related to such atmospheres: (1) understanding their primordial compositions from an experimental cosmochemistry approach, and (2) evaluating the planetary context for observable biosignature gases.

The first theme is motivated because, at present, there is no first-principles understanding of how to connect a planet’s bulk composition to its initial atmospheric properties. Since terrestrial exoplanets likely form their atmospheres through outgassing, a novel step towards building such a theory is to assay meteorites, the left-over building blocks of planets, by heating them to measure their outgassed volatiles. I utilized multiple experimental techniques to determine the outgassing composition of primitive meteorite samples over a wide range of temperatures and pressures. I will present the results of these experiments in which I heated carbonaceous chondrite samples and measured by mass spectrometry the abundances of major released volatile species as a function of temperature in a high-vacuum environment. I also performed complementary bulk element analysis on the samples before and after the heating experiments to monitor outgassing of heavier elements. Currently, I am performing additional outgassing experiments using a novel technique consisting of a thermogravimetric analyzer coupled to a gas chromatograph on enstatite chondrite samples. I will discuss how my experimental results compare to thermochemical equilibrium models of chondrite outgassing and how these experiments can help improve atmospheric models, including the connection between bulk composition and early atmospheric properties.

For the second theme, I performed a comprehensive analysis of the necessary planetary conditions for atmospheric methane to be a compelling biosignature gas. Since methane is one of the only biosignatures that JWST can readily detect in terrestrial atmospheres, it is essential to understand methane biosignatures to contextualize these imminent observations. I will present my work on determining the necessary planetary context for methane to be a compelling biosignature, based on a combination of multiphase thermodynamic and atmospheric chemistry models. This work investigated methane’s various abiotic sources and determined when, under different conditions, they could be enhanced on other planets to result in false positives.

For further information contact PALS coordinators Tad Komacek and Quanzhi Ye at and


Special accommodations for individuals with disabilities can be made by calling (301) 405-3001. It would be appreciated if we are notified at least one week in advance.


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