There's more to life than O${}_2$: Simulating the detectability of a range of molecules for ground-based high-resolution spectroscopy of transiting terrestrial exoplanets

Abstract

Within the next decade, atmospheric O${}_2$ on Earth-like M dwarf planets may be accessible with visible--near-infrared, high spectral resolution extremely large ground-based telescope (ELT) instruments. However, the prospects for using ELTs to detect environmental properties that provide context for O${}_2$ have not been thoroughly explored. Additional molecules may help indicate planetary habitability, rule out abiotically generated O${}_2$, or reveal alternative biosignatures. To understand the accessibility of environmental context using ELT spectra, we simulate high-resolution transit transmission spectra of previously-generated evolved terrestrial atmospheres. We consider inhabited pre-industrial and Archean Earth-like atmospheres, and lifeless worlds with abiotic O${}_2$ buildup from CO${}_2$ and H${}_2$O photolysis. All atmospheres are self-consistent with M2V--M8V dwarf host stars. Our simulations include explicit treatment of systematic and telluric effects to model high-resolution spectra for GMT, TMT, and E-ELT configurations for systems 5 and 12 pc from Earth. Using the cross-correlation technique, we determine the detectability of major species in these atmospheres: O${}_2$, O${}_3$, CH${}_4$, CO${}_2$, CO, H${}_2$O, and C${}_2$H${}_6$. Our results suggest that CH${}_4$ and CO${}_2$ are the most accessible molecules for terrestrial planets transiting a range of M dwarf hosts using an E-ELT, TMT, or GMT sized telescope, and that the O${}_2$ NIR and H${}_2$O 0.9 $\mu$m bands may also be accessible with more observation time. Although this technique still faces considerable challenges, the ELTs will provide access to the atmospheres of terrestrial planets transiting earlier-type M-dwarf hosts that may not be possible using JWST.

Accepted for publication in The Planetary Science Journal