Bayesian Analysis for Remote Biosignature Identification on exoEarths (BARBIE) \RNum{3}: Introducing the KEN

TL;DR

This study assesses the detectability of methane in Earth-like exoplanets using spectral data, highlighting the importance of spectral confusion and optimal bandpass selection for future space telescopes.

Contribution

It introduces a new spectral grid analysis method to evaluate methane detectability considering spectral confusion and different bandpass widths for upcoming exoplanet missions.

Findings

Modern-Earth methane is undetectable at typical SNRs.

Archean-Earth methane is detectable across all SNRs and bandpasses.

Methane detectability decreases with higher water vapor abundance.

Abstract

We deploy a newly-generated set of geometric albedo spectral grids to examine the detectability of methane (CH4) in the reflected-light spectrum of an Earth-like exoplanet at visible and near-infrared wavelengths with a future exoplanet imaging mission. By quantifying the detectability as a function of signal-to-noise ratio (SNR) and molecular abundance, we can constrain the best methods of detection with the high-contrast space-based coronagraphy slated for the next generation telescopes such as the Habitable Worlds Observatory (HWO). We used 25 bandpasses between 0.8 and 1.5 microns. The abundances range from a modern-Earth level to an Archean-Earth level, driven by abundances found in available literature. We constrain the optimal 20%, 30%, and 40% bandpasses based on the effective SNR of the data, and investigate the impact of spectral confusion between CH4 and H2O on the detectability of each one. We find that a modern-Earth level of CH4 is not detectable, while an Archean Earth level of CH4 would be detectable at all SNRs and bandpass widths. Crucially, we find that CH4 detectability is inversely correlated with H2o abundance, with required SNR increasing as H2O abundance increases, while H2O detectability depends on CH4 abundance and selected observational wavelength, implying that science requirements for the characterization of Earth-like planet atmospheres in the VIS/NIR should consider the abundances of both species in tandem.