Modern Earth-like Chemical Disequilibrium Biosignatures Are Challenging To Constrain Through Spectroscopic Retrievals

Abstract

Robust exoplanet characterization studies are underway, and the community is looking ahead toward developing observational strategies to search for life beyond our solar system. With the development of life detection approaches like searching for atmospheric chemical species indicative of life, chemical disequilibrium has also been proposed as a potentially key signature for life. Chemical disequilibrium can arise from the production of waste gases due to biological processes and can be quantified using a metric known as the available Gibbs free energy. The main goal of this study was to explore the detectability of chemical disequilibrium for a modern Earth-like analog. Atmospheric retrievals coupled to a thermodynamics model were used to determine posterior distributions for the available Gibbs free energy given simulated observations at various noise levels. In reflected light, chemical disequilibrium signals were difficult to detect and limited by the constraints on the CH4 abundance, which was challenging to constrain for a modern Earth case with simulated observations spanning ultraviolet through near-infrared wavelengths with V-band SNRs of 10, 20, and 40. For a modern Earth analog orbiting a late-type M dwarf, we simulated transit observations with the James Webb Space Telescope Mid-Infrared Instrument (MIRI) and found that tight constraints on the available Gibbs free energy can be achieved, but only at extremely low noise on the order of several ppm. This study serves as further proof of concept for remotely inferring chemical disequilibrium biosignatures and should be included in continuing to build life detection strategies for future exoplanet characterization missions.

arXiv comment25 pages, 17 figures. Accepted to ApJ. Accessible figure data: https://doi.org/10.5281/zenodo.15485517 Python Thermodynamics Model: https://github.com/Bellatrix12/Python_Equilibrium_Code.git

References in corpus (34)

• emcee: The MCMC Hammer
• The Transiting Exoplanet Survey Satellite
• Prevalence of Earth-size planets orbiting Sun-like stars
• The Occurrence Rate of Small Planets around Small Stars
• A Temperature and Abundance Retrieval Method for Exoplanet Atmospheres
• Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life
• Biosignatures from Earth-Like Planets Around M Dwarfs
• Atmospheric Retrieval for Super-Earths: Uniquely Constraining the Atmospheric Composition with Transmission Spectroscopy
• Characterizing transiting exoplanet atmospheres with JWST
• A Systematic Retrieval Analysis of Secondary Eclipse Spectra I: A Comparison of Atmospheric Retrieval Techniques
• Exoplanet Biosignatures: Understanding Oxygen as a Biosignature in the Context of Its Environment
• The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth
• The Detectability and Characterization of the TRAPPIST-1 Exoplanet Atmospheres with JWST
• Disequilibrium biosignatures over Earth history and implications for detecting exoplanet life
• Detectability of biosignatures in anoxic atmospheres with the James Webb Space Telescope: A TRAPPIST-1e case study
• On Correlated-noise Analyses Applied To Exoplanet Light Curves
• UV Surface Environment of Earth-like Planets Orbiting FGKM Stars Through Geological Evolution
• Pale Orange Dots: The Impact of Organic Haze on the Habitability and Detectability of Earthlike Exoplanets
• Detectability of atmospheric features of Earth-like planets in the habitable zone around M dwarfs
• On detecting biospheres from chemical thermodynamic disequilibrium in planetary atmospheres
• Characterizing Earth Analogs in Reflected Light: Atmospheric Retrieval Studies for Future Space Telescopes
• A comparison of exoplanet spectroscopic retrieval tools
• Analysis of a JWST NIRSpec Lab Time Series: Characterizing Systematics, Recovering Exoplanet Transit Spectroscopy, and Constraining a Noise Floor
• The Occurrence Rate of Terrestrial Planets Orbiting Nearby Mid-to-late M Dwarfs from TESS Sectors 1-42
• Developing Atmospheric Retrieval Methods for Direct Imaging Spectroscopy of Gas Giants in Reflected Light I: Methane Abundances and Basic Cloud Properties
• A Theory of Exoplanet Transits with Light Scattering
• Sensitive Probing of Exoplanetary Oxygen via Mid Infrared Collisional Absorption
• Detectability of Molecular Signatures on TRAPPIST-1e through Transmission Spectroscopy Simulated for Future Space-Based Observatories
• The K Dwarf Advantage for Biosignatures on Directly Imaged Exoplanets
• Effects of UV stellar spectral uncertainty on the chemistry of terrestrial atmospheres
• Exploring and Validating Exoplanet Atmospheric Retrievals with Solar System Analog Observations
• Is ozone a reliable proxy for molecular oxygen? I. The O2-O3 relationship for Earth-like atmospheres
• A Catalogue of Exoplanet Atmospheric Retrieval Codes
• Inferring Chemical Disequilibrium Biosignatures for Proterozoic Earth-Like Exoplanets