Abstract EANA2026-49

Introduction

The Rochette member (Lower Maaz formation, Jezero Crater) preserves evidence of aqueous alteration within its secondary mineralogy, including phyllosilicates and evaporites, which are critical in the assessment of past habitability of Mars [1-3]. Phyllosilicates, in particular, are key indicators of fluid-rock interactions and have been shown to preserve potential biosignatures such as organics [4]. In this study, we combine thermochemical modelling and Martian simulation experiments to evaluate habitability and biosignature formation within the geochemical environment surrounding the phyllosilicate-forming alteration phase of Rochette.

Methods

CHIM-XPT [5], a thermochemical modelling program, was used to reconstruct the geochemical conditions of phyllosilicate formation at Rochette. These models combined the Los Angeles meteorite, which served as an analogue for an unaltered Rochette precursor, with a simulated Martian groundwater composition [6], which yielded precipitation of secondary minerals pertinent to Rochette, under diagenetic conditions (~25°C; alkaline pH; Si/Ca/Na-rich, Mg/P-depleted fluid with reduced sulfur).

The models predicted a growth medium used for experiments (with and without additional organics in Jezero-relevant concentrations). The media was adapted to satisfy CHNOPS requirements through the addition of nitrates and combined with a regolith analogue (Los Angelese Derived Simulant (LADS)). Experiments were conducted under abiotic and biotic conditions, alongside LADS-free and dead cell controls. The experimental inoculum was a mixed microbial community from Caldy Beach intertidal zone (a recognised Martian analogue) [7], selectively grown through successive subculturing to favour microorganisms best adapted to experimental conditions. Cell growth, pH and chemical changes (monitored with ICP-OES, ferrozine assay (for Fe(ii)/Fe(iii) ratio), and Cline assay (for HS- concentration)) were assessed throughout the experiment. 16s rRNA sequencing was used to characterise the microbial communities within the experiments, and SEM and Raman spectroscopy were used to assess biosignature formation in post-experimental regolith samples.

Preliminary Results and Discussion

Preliminary results demonstrate microbial growth was heavily reliant on the presence of LADS and was strongly influenced by the addition of organics. The pH of the environment was influenced by both the presence of organics (-ΔpH), and microbial growth(+ΔpH). 16s rRNA results will provide further understanding of the potential metabolic pathways employed by the community, and chemical and spectroscopic analyses will further elucidate the biogenicity and biosignature preservation potential of the environment.

Conclusion

This study bridges geochemistry and microbiology to bolster our understanding of the habitability under the unique conditions present during the phyllosilicate-forming phase of alteration at the Jezero crater floor. The integration of these fields through modelling and experimental approaches refines our understanding of habitability and biosignatures in this key Martian region, with direct implications for the ongoing Mars 2020 mission.

[1] Farley et al, 2022, Science; [2] Simon et al, 2023, JGR Planets; [3] Schmidt et al, 2025, Science Advances; [4] Tu et al, 2021, Minerals; [5] Reed et al, 2010: Users Guide for CHIM-XPT; [6] Bridges et al, 2015, JGR Planets; [7] Curtis-Harper et al, 2018, Microorganisms