Abstract EANA2026-79

Search for organic matter on Mars is primary for astrobiology-focused missions because of the planet’s rich aqueous geological history and potential for harboring biosignatures. Organics are indeed the most direct chemical tracers of carbon cycling, prebiotic chemistry, and potential past life, being crucial to identify biosignatures on the planet. However, their detection alone is not necessarily sufficient to demonstrate biogenicity[1]. Key is the distinction between simple or refractory organic compounds that may form abiotically, like polycyclic aromatic hydrocarbons (PAHs), and biomolecules like proteins, nucleic acids or pigments that are more diagnostically suggestive of life. 

Evaporites are particularly interesting for biosignatures detection because of its high fossilization potential[2][3], given their ability to efficiently trap and shield organic compounds within their mineral matrices for long times[4][5], therefore protecting them from oxidizing agents and radiations. Although evaporites precipitation is mainly driven by evaporation and subsequent supersaturation, on Earth, microorganisms can influence nucleation pathways[6][7], producing evaporites possibly enriched in organic molecules. Organo-evaporites associations are common; for carbonates this could be due to selective adsorption processes by calcium sites on the surface of the mineral[8], while for sulfates the associations are likely due to the incorporation of organics within the mineral matrix. Organo-evaporites associations were often also in extraterrestrial materials like meteorites and even on Mars, suggesting that these associations can emerge naturally during water-rich parent-body processing without requiring any biological input.

This work aims to understand: (1) how two different model organic molecules, a biomolecule and an abiotic compound, distribute throughout two different minerals in an abiotic desiccation process; (2) if and how the two model organic molecules affect the re-crystallization of the two minerals; (3) how to distinguish between a potential biosignature and a model abiotic organic compound with payload-analog techniques.

To achieve these goals, a set of 12 samples (including blanks) was prepared using calcium sulfate, calcium carbonate, β-Carotene and 9-methyl anthracene (9MA). Minerals bearing the same cation were chosen to focus on the role of the carbonate (CO32–) and sulfate (SO42–) anions in the interaction with the organic molecules. The molecules were chosen to represent a biomolecule strongly suggestive of life and an abiotic compound. β-Carotene was chosen as the biotic model, being a pigment commonly present in plants, algae, cyanobacteria, fungi and yeasts. As abiotic, 9MA (a PAH) was selected as it is considered as a possible explanation for Quartier abrasion spectroscopic features[1], and because methylated PAHs are very common in meteorites[9], thus not strictly diagnostic for life.

The samples were characterized at the INAF-Astrophysical Observatory of Arcetri, by performing: (1) infrared spectrometry with Bruker VERTEX 70v Fourier Transform InfraRed spectrometer (range 8000cm–1-400cm–1, resolution of 4cm–1); (2) DUV fluorescence with DUV Raman PL 200 instrument by Photon Systems (248.6 nm excitation laser, range 250 nm-620 nm, resolution of 1.2 nm).

The data were analyzed to detect spectral and spatial distribution variations, evaluating correlations between the organics and the minerals bands.

 

Acknowledgements: This work was supported by ASI/INAF 2023-3-HH.0 agreement. This abstract and related research have been conducted during and with the support of the Italian national inter-university PhD programme in Space Science and Technology.

 

References:

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