Detecting Biosignatures of Nearby Rocky Exoplanets: Simulations of High Spectral Resolution Observations with the ELTs

The imminent arrival of the Extremely Large Telescopes (ELTs) will finally deliver the observational power capable of assessing the habitability of nearby rocky exoplanets. The ELT presents us with the exciting opportunity of being able to spatially resolve the terrestrial exoplanet Proxima b, which lies in the habitable zone of Proxima Centuri. This would allow molecule mapping, a technique that uses the spatial separation plus cross correlation high resolution spectroscopy to disentangle the planet's spectrum from the host star and characterise its atmosphere. Here we present simulations in reflected light for the High Contrast Adaptive Optics (HCAO) mode of HARMONI/ELT, using model planet spectra from the Carl Sagan Institute designed specifically for Proxima b and its M-dwarf host star. HARMONI's resolution (R=17,385) is well suited to molecule mapping, with access to wavelengths covering multiple biosignatures. Our simulator shows that this first light ELT instrument can characterise the atmosphere of Proxima b, within a very reasonable time frame, but requires intervention on the focal plane masks in HARMONI's current instrument design. If changed, HARMONI has the potential to identify CO2, CH4, and H2O in Proxima b. Our simulator is highly versatile and we are extending to other instruments for the ELTs, including METIS/ELT and GMagAO-X+IFS/GMT.