Responses of Climate and Atmospheric Biosignatures on Earth-like Planets and Detectability with the Large Interferometer for Exoplanets (LIFE)

Abstract

We investigate the detectability of atmospheric biosignatures with the 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 10pc for the instrument baseline case. We find that atmospheric ozone (O3) abundances are present over a range of conditions. The O3 fundamental band is present 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) are favored for low UV conditions e.g. exoplanets orbiting cooler central stars or having strong atmospheric shielding. Regarding spectral signatures, CH4 and water (H2O) signals in the near infrared are evident in most scenarios, as is the carbon dioxide (CO2) fundamental band, which strengthens for low-O2 scenarios associated with upper atmosphere cooling. Regarding detectability by LIFE (20-day viewing, baseline case), H2O was retrievable with a confidence level (CL) of up to 3-sigma for the high (90%, 0.9 vmr) CO2 scenario, and with ~2-sigma or less for the other scenarios. CO2 would be detectable with high significance, having a CL sigma range of (6.2-9.4) for the various scenarios. N2O would not be observable with a CL sigma mostly in the range (1-2). CH4 featured a CL sigma detectability range of [2.3 to 4.4]. O3 was detectable with a CL (>3-sigma) in all scenarios (including the low -ozone Proterozoic) except for the xtremely low O3 Archaean scenario.