Bayesian Analysis for Remote Biosignature Identification on exoEarths (BARBIE). IV. Analyzing CO ₂ Detections in the Near-IR to Determine the Long-wavelength Cutoff for the Habitable Worlds Observatory Coronagraph

Abstract We present our analysis of how the detectability of carbon dioxide (CO 2 ) on an Earth-like planet varies with respect to signal-to-noise ratio (SNR), wavelength, and molecular abundance. Using the Bayesian Analysis for Remote Biosignature Identification on exoEarths methodology, we can determine the optimal long-wavelength cutoff for the future Habitable Worlds Observatory coronagraph. We test 25 evenly spaced 20% bandpasses between 0.8 and 2.0 μ m, and simulate data spanning a range of SNRs and molecular abundance to analyze the relationship between wavelength and detectability for different planetary archetypes. We examine abundance levels from varying Earth epochs and a Venus-like archetype to investigate how detectability would change throughout the evolution of a rocky planet. Here, we present our results on the planetary conditions and technological requirements to strongly detect CO 2 . In addition, we analyze the degeneracy of CO 2 with carbon monoxide (CO), methane (CH 4 ), and water (H 2 O). We determine that any abundance of CO does not achieve strong detections and that CH 4 and H 2 O play a pivotal role in the ability to detect CO 2 . We conclude that the optimal long-wavelength cutoff for the Habitable Worlds Observatory coronagraph should be 1.68 μ m.