Abstract EANA2025-165

One of the aims of Astrobiology is to search for life signs elsewhere in the universe. Most life-detection studies focus on oxygenic biosignatures tackling only exoplanets similar to modern Earth. This leaves a noticeable knowledge gap between the similarly abundant and potentially inhabited exoplanetary anoxic environments.

Many anoxygenic gas molecules can be powerful biosignatures such as CH3SH, CH3S2CH3, CH3Cl, N2O, NO2, NH3 and OCS, but are not easily studied experimentally. Models such as RASCALL will be useful for predicting the infrared spectra of gaseous biosignatures. 

In this study, several gas molecules of interest, linked to anoxygenic metabolisms were studied within the infrared spectroscopy prediction model RASCALL. Molecules containing the chloride functional group like CH3Cl, C2H5Cl, C3H7Cl, C3H4ClN and C2H3ClO were the most studied, with their predictions being corrected according to organic and inorganic chemistry concepts, namely hyperconjugation and negative hyperconjugation in regards to a molecule’s stability. Although not all molecules studied are considered good biosignatures (some don’t have a known biotic pathway), key molecules were used to increase the amount of data and improve the predictions’ fidelity. Moreover, a literature search was performed to identify anoxygenic metabolisms from microbial extremophiles, to explore the potential for habitability in exoplanet-like anoxic environments, such as Early Earth (3800-2500 million years ago) and the exoplanets known as “Cold Haber Worlds”. These exoplanets are defined as having a thick atmosphere made of N2 and H2 with a deep ocean underneath. A potential biosignature for this environment would be NH3, produced by bacteria like Clostridium pasteurianum and the anammox (ammonium-oxidizing) bacteria Scalindua profunda japonica.