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Abstract EANA2024-36


Abiotic synthesis of potential biosignatures on terrestrial planets

Jaroslav Kačina (1,2), Klaudia Mráziková(1), Antonín Knížek(1,3), Homa Saeidfirozeh(1), Lukáš Petera(1,4), Svatopluk Civiš(1), Franz Saija(5), Giuseppe Cassone(5), Paul B. Rimmer(6), Kateřina Němečková (1) and Martin Ferus(1)
(1) J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Prague, Czechia. (2) Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University, Prague, Czechia. (3) Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Prague, Czechia. (4) Department of Inorganic Chemistry, Faculty of Science, Charles University, Prague, Czechia. (5) Institute for Physical-Chemical Processes, National Research Council of Italy (IPCF-CNR), Messina, Italy. (6) University of Cambridge, Cavendish Astrophysics, Cambridge, United Kingdom.


Recent ground-based observations by Greaves et al. [1] have detected a spectral feature consistent with phosphine (PH­­3) in Venus' middle atmosphere, suggesting a potential biosignature on rocky planets. The presence of PH3 in Venus' oxidized atmosphere remains unexplained by known processes. While some studies challenge the detection due to data analysis and potential coincidence with the SO2  line, reanalysis confirms a PH3 signal around 5 ppm [1]. This finding is supported by reanalysis of legacy data from NASA's Pioneer Venus Neutral Gas Mass Spectrometer at 51.3 km altitude. Experimental and theoretical research has shown that methane can form photochemically from carbon dioxide on Mars' acidic mineral surfaces, involving HC·O radicals [2]. Quantum-mechanical calculations suggest a similar radical chemistry process on Venus, where the reaction of PO· with HC·O, produced by the reduction of CO2 over acidic dust under UV-A radiation, could lead to PH3 formation. Key intermediates in this process include HPO, H2P·O, and H3P·OH[3]. This process is analogous to methane formation predicted over photocatalytic acidic minerals on Mars and the photoreduction of N2 to NH3 observed on Earth's minerals under sunlight. Recent studies have also demonstrated photocatalytic NH3 production from N2O. Thus, radical chemistry over acidic aerosols may explain the presence of PH3, NH3, and CH4 in planetary atmospheres, and these processes must be taken into account if reduced species are considered as biomarkers in the atmospheres of Mars, Venus, and exoplanets [3].

 

[1]  GREAVES, Jane S., et al. Phosphine gas in the cloud decks of Venus. Nature Astronomy, 2021, 5.7: 655-664.

[2] CIVIŠ, Svatopluk, et al. The origin of methane and biomolecules from a CO2 cycle on terrestrial planets. Nature Astronomy, 2017, 1.10: 721-726.

[3] MRÁZIKOVÁ, Klaudia, et al. A Novel Abiotic Pathway for Phosphine Synthesis over Acidic Dust in Venus' Atmosphere. Astrobiology, 2024, 24.4: 407-422.