Detectability of Atmospheric Climate and Biosignatures with the Large Interferometer for Exoplanets (LIFE) for Terrestrial-type Exoplanets

We investigate the detectability of atmospheric biosignatures with the Large Interferometer for Exoplanets (LIFE) mission. Starting with the modern Earth we model the climate, photochemistry, and spectra of Earth-like planets over a range of insolation, gravity, humidity, albedo, atmospheric mass, and carbon dioxide abundances, and investigate detectability of key atmospheric species by LIFE for Earth-like planets assumed to lie at 10 pc for the LIFE (20-d viewing) baseline case. We find that atmospheric ozone (O3) abundances are maintained over a range of conditions. The O3 fundamental band is visible for most scenarios studied but is weakened for exoplanets with cooler central stars. Additional potential biosignatures such as methane (CH4), nitrous oxide (N2O), and chloromethane (CH3Cl) have larger abundances for low UV conditions e.g. exoplanets orbiting cooler central stars or having strong atmospheric shielding. Regarding spectral signatures, CH4 and water (H2O) signals from 6–8 μm are evident in most scenarios, as is the carbon dioxide (CO2) 15 μm band, which strengthens for low-O2 scenarios associated with upper atmosphere cooling. Considering a 20-d viewing, H2O is retrievable with a confidence level (CL) of 3.6σ for an Earth-like planet orbiting a cool star. N2O is not observable with a CL sigma mostly less than one for the scenarios considered. CH4 features a CL sigma detectability range of up to 1.5. O3 is detectable in most cases with a CL of ~2.0 to 3.0 (including the low-ozone Proterozoic) except for the extremely low O3 Archaean scenario and the low-pressure atmosphere scenario.