Detecting Biosignatures and Pre-Biosignatures in the Atmospheres of Earth-like Planets Around Other Stars

When we observe the first terrestrial exoplanet atmospheres, we expect to find planets at a wide range of geological conditions and evolution. In our own Solar System we already have three very different terrestrial exoplanets in Earth, Mars, and Venus. Additionally the atmospheres of these planets have not been fixed in time. Earth itself offers many possible atmospheric states of a planet. We set out to examine how an Earth-like planet at different geological epochs might look around other star types (F, G, K and M dwarf stars). We look at the rise of oxygen and the detectability of combinations of biosignature gases throughout Earth history, modeling the great oxygenation event and Neoproterozoic oxygenation event event around other star types. We show the VIS - IR spectral features, with a focus on biosignatures observable through geological time for FGKM stars and the effect of clouds on the signal. Additionally, we examine the plausibility of detecting prebiotically interesting molecules, such as HCN, NH3, CH4, and C2H6 in an early-Earth type atmosphere. We find that some of these molecules could be produced abiotically in a CO2/CH4/H2 rich atmosphere with lighting and photochemistry. These molecules would be interesting to detect in an exoplanet atmosphere since they are known to be useful for key prebiotic chemical pathways. HCN, for example, is present at each of the initial photochemical reactions that produce lipids, amino acids and nucleosides, the three building blocks of life.

Followed by wine and cheese in Pupin 1332.

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