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

Abstract

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 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 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 , 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 μ 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.

Keywords

• Astrobiology
• Biosignatures
• High resolution spectroscopy
• Exoplanet atmospheres
• Ground-based astronomy