Abstract DGP2026-3

Oxygen bistability and triple signature false positives in emission spectra of terrestrial exoplanet atmospheres

Benjamin Taysum (1) Sarah Rugheimer (2,3) John Lee Grenfell (1) Franz Schreier (4) Juan Cabrera (1) Heike Rauer (5,6)

(1) Institut für Weltraumforschung (WF), Deutsches Zentrum für Luft-und Raumfahrt (DLR), Rutherfordstraße 2, Berlin, 12489, Germany (2) School of Physics and Astronomy, University of Edinburgh, James Clerk Maxwell Building, Edinburgh, EH9 3FD, United Kingdom (3) Department of Physics and Astronomy, York University, Street, York, M3J 1P3, Ontario, Canada (4) Institut für Methodik der Fernerkundung (IMF), Deutsches Zentrum für Luft- und Raumfahrt (DLR), Münchener Straße 20, Weßling, 82234, Germany (5) Freie Universität Berlin (FUB), Fachbereich Geowissenschaften, Institut für Geologische Wissenschaften, Malteserstraße 74-100, 12249, Berlin, Germany (6) Deutsches Zentrum für Luft- und Raumfahrt (DLR), Markgrafenstraße 37 10117 Berlin, Germany

The detection of life on a rocky exoplanet currently hinges upon identifying the planet’s atmospheric composition. Photochemical modelling studies routinely show that it is challenging, if not impossible, to attribute the detection of any singular molecular species exclusively to biological production. The simultaneous detection of CO2 , O3 , and H2O (‘Triple Signature’) is however regarded as a robust indicator of oxygenic photosynthetic processes on the surface of an Earth-like exoplanet. In this study, we use a 1D climate-chemistry coupled atmospheric model to investigate the Triple Signature in emission spectra across 4.0-18.5 µm. The study focuses on abiotic planets with N2-based atmospheres throughout the habitable zone [0.95 au, 1.37 au] of a Sun-like (G2). Results suggest that a critical orbital distance exists that is dependent on pCO2 and the total H2O column which dictates the atmospheric O2 content and the ability of the Triple Signature to be produced abiotically. Positioned at this critical distance, an increase of stellar flux of less than 1% is sufficient to cause the abiotic O2 columns of the planet to collapse from 0.01-0.30 PAL to below 10^-4 PAL and remove the O3 detection from the Triple Signature. A total of 5000 abiotic atmospheres initialised with a randomly sampled range of CO2 partial pressures [1 mbar, 100 mbar], H2O columns [100 ppmv, 10000 ppmv], and orbital distances [0.95 au, 1.37 au] are studied with LIFEsim to identify the integration time required for CO2 , H2O, and O3 to produce 3-σ significant absorption features in the planet emission spectra for the LIFE interferometer.