There's More to Life than O₂: Simulating the Detectability of a Range of Molecules for Ground-based, High-resolution Spectroscopy of Transiting Terrestrial Exoplanets

Within the next decade, atmospheric O-2 on Earth-like M-dwarf planets may be accessible with visible-near-infrared (NIR), high-spectral-resolution, ground-based extremely large 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 preindustrial and Archean Earth-like atmospheres, and lifeless worlds with abiotic O-2 buildup from CO2 and H2O 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 Giant Magellan Telescope (GMT), Thirty Meter Telescope (TMT), and European ELT (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, CH4, CO2, CO, H2O, and C2H6. Our results suggest that CH4 and CO2 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 H2O 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.