The Detectability and Constraints of Biosignature Gases in the Near- and Mid-infrared from Transit Transmission Spectroscopy

Abstract

The James Webb Space Telescope is expected to revolutionize our understanding of Jovian worlds over the coming decade. However, as we push toward characterizing cooler, smaller, terrestrial-like planets, dedicated next-generation facilities will be required to tease out the small spectral signatures indicative of biological activity. Here, we evaluate the feasibility of determining atmospheric properties, from near-to-mid-infrared transmission spectra, of transiting temperate terrestrial M-dwarf companions. Specifically, we utilize atmospheric retrievals to explore the trade space between spectral resolution, wavelength coverage, and signal-to-noise on our ability to both detect molecular species and constrain their abundances. We find that increasing spectral resolution beyond R  = 100 for near-infrared wavelengths, shorter than 5 μ m, proves to reduce the degeneracy between spectral features of different molecules and thus greatly benefits the abundance constraints. However, this benefit is greatly diminished beyond 5 μ m as any overlap between broad features in the mid-infrared does not deconvolve with higher resolutions. Additionally, our findings revealed that the inclusion of features beyond 11 μ m did not meaningfully improve the detection significance or the abundance constraints results. We conclude that an instrument with continuous wavelength coverage from ∼2 to 11 μ m, spectral resolution of R  ≃ 50–300, and a 25 m 2 collecting area, would be capable of detecting H 2 O, CO 2 , CH 4 , O 3 , and N 2 O in the atmosphere of an Earth-analog transiting a M dwarf (mag K = 8.0) within 50 transits, and obtain better than an order-of-magnitude constraint on each of their abundances.