Examining the detectability of chemical disequilibrium biosignatures and optimizing observing strategies for future exoplanet characterization missions

Young, Amber Vanessa (2023) Examining the detectability of chemical disequilibrium biosignatures and optimizing observing strategies for future exoplanet characterization missions. Doctoral thesis, Northern Arizona University.

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Abstract

The field of exoplanet science is accelerating towards our first opportunities to observe and characterize distant worlds for their ability to host life. Chemical disequilibrium has long been proposed as a potential indicator of life and is rooted in the idea that life can substantially influence its environment due to waste gases produced from life's metabolic processes. Because this signature is not specific to a given metabolic process, it offers a potentially agnostic biosignature to search for on exoplanets. However, very few studies have been done to understand its ability to be inferred from noisy spectral observations. Alongside these efforts, now is a crucial time to develop observational strategies for future exoplanet characterization efforts that balance biosignature-focused, detailed atmospheric characterization against complex mission constraints on exposure times and observing windows. Across three different manuscripts, we tested our ability to remotely infer chemical disequilibrium biosignatures by coupling a retrieval model to a thermodynamics model to quantify chemical disequilibrium and understand its sensitivity to observational uncertainty. We explored the potential to constrain the chemical disequilibrium of modern Earth with simulated direct imaging and transit observations and showed that the coupling process between retrievals and the thermodynamics model was successful. In a separate study, we explored approaches to remote sensing of the chemical disequilibrium of Proterozoic Earth and highlighted the observational requirements needed by future direct imaging to enable those inferences. Finally, in the last paper we took an observational decision tree strategy that lays out a roadmap for conducting a search for biosignatures (and evidence for planet habitability) and executed each level of the decision tree with retrieval modeling. In this study, we demonstrated the utility of the decision tree for characterizing both a modern Earth-like and Archean Earth-like exoplanet analog. As a whole, these studies advance strategies for exoplanet characterization by investigating the remote detectability of agnostic biosignatures like chemical disequilibrium and validating preliminary observational strategies that could be used to inform future exoplanet direct imaging missions that are on the horizon.

Item Type:	Thesis (Doctoral)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	Astrobiology; Biosignatures; Chemical Disequilibrium; Exoplanets
Subjects:	Q Science > QB Astronomy
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > Physics and Astronomy
Date Deposited:	07 Aug 2026 17:52
Last Modified:	07 Aug 2026 17:52
URI:	https://openknowledge.nau.edu/id/eprint/6339

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