Abstract EANA2025-32

The James Webb Space Telescope (JWST) offers the possibility to detect biosignatures in transiting exoplanet atmospheres via transmission spectroscopy.

There are numerous studies trying to make predictions how many transit observations would be required to detect possible biosignatures with a certain confidence. In most cases M-dwarf stars are taken, because they offer the possibility to observe many transits as the rotational period of exoplanets around M-dwarfs in the habitable zone is only in the order of a few days. Additionally they offer large planet to star radius ratios which is beneficial for transmission spectroscopy. However, the detection of biosignatures is still very challenging and depends on many parameters as atmospheric characteristics of the exoplanet, spectral properties of the host star, distance to Earth and of course the respective biosignatures.

This study analyses and clusters the current findings from a physical point of view. It does not discuss biosignatures it mainly focus on the detectability of the currently discussed molecules which are suspected of possibly being biosignatures.

It concludes that the detectability of possible biosignatures can be predicted in a quantitative way only for very specific conditions based on many assumptions. Even when taking the same exoplanet and host star as a reference, the detectability of each biosignature varies extremely by assumptions on atmospheric conditions.  

From a qualitative point of view it may be drawn the conclusion that the CO2-CH4 disequilibirum pair may be detected with rather few transits between 10 and 20 and that O2/O3 is rather impossible to be detected with JWST as the required transits are more than 100 which is even for an M-dwarf no acceptable observation time.

From an astrobiological point of view, it may be discussed whether the locations where we search for life are mainly determined by technical conditions.