Abstract EANA2026-36

Guided by the European Astrobiology Roadmap, serpentinization sites are prime targets for studying the origins of life. In mafic and ultramafic crust on both Earth and Mars, olivine hydration yields serpentine, magnetite, brucite and molecular hydrogen (H₂). This H₂ can fuel microbial metabolism or drive the abiotic Fischer-Tropsch-type synthesis of organic compounds such as methane. Given reported transient methane detections in the Martian atmosphere and spectroscopic evidence consistent with aromatic organic molecules in Jezero crater, serpentinizing systems represent important analogues for assessing planetary habitability, abiotic organic synthesis, and biosignature preservation. Hence, terrestrial serpentinizing systems are valuable analogues for studying the links between water–rock reactions, microbial communities, and potential biosignatures under conditions relevant to subsurface habitability on Mars.

The Cabeço de Vide (CdV) ultramafic massif in Portugal provides an active terrestrial laboratory for continental serpentinization. Its serpentinized ultramafic rocks and hyperalkaline aquifer make CdV a relevant analogue for water–rock interaction processes in Martian ultramafic terrains, including olivine-, pyroxene-, carbonate-, and serpentine-bearing settings associated with Jezero and the surrounding Nili Fossae region. CdV is one of the few continental serpentinizing systems with an active hyperalkaline aquifer, where Type II Ca–OH/Na–Cl waters reach pH values of ~11.5 and host microbial communities.

We combined three complementary approaches. First, 23 depth-resolved core samples from borehole AC2 (10–121 m) were characterized by XRD, Raman spectroscopy, LIBS, SEM-EDS, FTIR, and bulk ICP-OES/MS to constrain mineralogical, petrographic, and geochemical variations from less altered protoliths to highly serpentinized horizons. These data were compared with lipid biomarker assemblages and metabarcoded microbial communities from corresponding depths to evaluate relationships among alteration state, microbial community structure, and potential biosignatures. Second, Sulfúrea waters were characterized hydrogeochemically and microbiologically, confirming the abundance of the facultative chemolithoautotroph Hydrogenophaga flava and the hydrogen-oxidizing Serpentinomonas mccroryi, and allowing the isolation of Serpentinomonas sp. Third, selected sterilized CdV samples were re-inoculated in filtered Sulfúrea water under H₂-rich conditions and monitored through time using analytical approaches relevant to Mars rover payloads, to assess which spectral, mineralogical, and chemical signatures of microbial colonisation remained detectable. The colonised rocks were then subjected to UV-C irradiation, Fe²⁺/H₂O₂ Fenton oxidation, and freeze–thaw cycling to evaluate how serpentinized mineral matrices influenced the preservation or degradation of organic biosignatures.

These approaches reveal that the CdV mineral suite directly mirrors Jezero Crater's olivine–serpentine–carbonate assemblage. Within this analogous environment, recovered lipids and their δ¹³C signature (-24 to -30‰) indicate an active bacterial community fueled by serpentinization-derived H₂, demonstrating the capacity of these serpentinizing environments to effectively preserve lipid biosignatures.

Ultimately, this study highlights CdV as an active continental serpentinization analogue for linking host-rock alteration, subsurface microbial communities, and the preservation of potential biosignatures. The CdV Serpentinomonas isolate provides a defined, cultivable model organism for controlled experiments on microbial colonisation and biosignature detectability under hyperalkaline, H₂-rich conditions. By combining mineralogical, geochemical, microbiological, and flight-relevant analytical approaches, this work provides constraints for interpreting biosignature preservation in serpentinized ultramafic rocks and for assessing their relevance to Martian habitability.

Acknowledgements: This work was funded by the Fundação para a Ciência e Tecnologia (FCT), through GeoBioTec research unit (UIDB/04035/2025, https://doi.org/10.54499/UID/04035/2025) and PhD grants R. Rebelo (2024.03653.BD), M. Grilo (2025.04772.BD)  and P. Gatinho  (2024.00316.BD). A. Gómez-Arias acknowledges her contract DGP_POST_2024_01054 funded by Junta de Andalucía/CUII and FSE+. This work was also supported by the HERMES R+D project (ref. PID2024-162087NB-C21) funded by the Spanish Ministry of Science, Innovation and Universities (MCIN/AEI/10.13039/501100011033).