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

TL;DR

This study assesses the feasibility of detecting biosignature gases in terrestrial exoplanet atmospheres using near- to mid-infrared transmission spectroscopy, highlighting optimal instrument parameters for future observations.

Contribution

It provides a detailed analysis of how spectral resolution, wavelength coverage, and signal-to-noise affect biosignature detection in exoplanet atmospheres, guiding future instrument design.

Findings

Higher spectral resolution (R=100) improves molecular abundance constraints below 5μm.

Wavelength coverage beyond 11μm does not significantly enhance detection or constraints.

A 25m² telescope with R=50-300 from 2-11μm can detect key biosignatures in Earth-like planets within 50 transits.

Abstract

The James Webb Space Telescope (JWST) is expected to revolutionize our understanding of Jovian worlds over the coming decade. However, as we push towards 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$\mu$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$\mu$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$\mu$m did not meaningfully improve the detection significance nor abundance constraints results. We conclude that an instrument with continuous wavelength coverage from $\sim$2-11$\mu$m, spectral resolution of R$\simeq$50-300, and a 25m$^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.