¹I. Criouet, ²S. Bernard, ¹E. Balan, ²F. Baron, ³A. Buch, ¹F. Skouri-Panet, ¹M. Guillaumet, ¹L. Delbes, ¹L. Remusat, ¹J.-C. Viennet
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2025.116789]
¹Muséum National d’Histoire Naturelle, Sorbonne Université, UMR CNRS 7590, Institut de minéralogie, de physique des matériaux et de cosmochimie, Paris, France
²Université de Poitiers, CNRS, Institut de Chimie des Milieux et Matériaux de Poitiers (IC2MP) UMR, 7285 Poitiers, France
³Laboratoire Génie des Procédés et Matériaux, CentraleSupélec, Gif-sur-Yvette, France
Copyright Elsevier

Clay-rich Martian rocks are considered promising targets in the search for fossilized remains of ancient Martian life. However, the actual influence of the clay mineral compositions in preserving microbial biosignatures remains poorly understood. Here, we explore the biopreservation potential of three pure smectites typically found on Mars and containing Al in their tetrahedral sheets (i.e. a Mg-rich, a Fe-rich and a Al-rich smectite), relying on experiments run using E. coli as a biological analog to simulate hydrothermal alteration scenarios relevant to Mars. The results show that Mg-rich smectites (saponite) are more effective at preserving biomolecules from thermal degradation than Fe-rich and Al-rich smectites (nontronite and beidellite). Plus, in contrast to saponite, neither nontronite nor beidellite appears to significantly trap (and thus preserve) organic compounds within their interlayer spaces. Overall, the present study highlights that both the chemistry and the quantity of organic materials in ancient Martian clay-rich rocks will depend on the compositional nature of smectites initially present.

¹Isabella Pignatelli,²Enrico Mugnaioli,¹Yves Marrocchi,^2,3Luigi Folco
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70031]
¹CRPG UMR 7358 CNRS-UL, Université de Lorraine, Vandœuvre-lès-Nancy Cedex, France
²Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy
³CISUP, Center for Instrument Sharing of the University of Pisa, Pisa, Italy
Published by arrangement with John Wiley & Sons

The Nakhla Martian meteorite is known to contain secondary minerals, in particular phyllosilicates, that have recorded the conditions of aqueous alteration of the parent rock. A section of this meteorite was analyzed by transmission electron microscopy to characterize the phyllosilicates in veins and mesostasis. High resolution and electron diffraction, combined with chemical data, suggest the presence of veins in olivine filled by carbonates and hisingerite or hisingerite alone. In the mesostasis, phyllosilicates with composition close to that of ferripyrophyllite were observed in rounded pores within feldspars—these phyllosilicates are associated with areas rich in Si likely due to the presence of amorphous silica. Iron oxides/hydroxides were not found in this study. In addition, for the first time, wadsleyite was observed within the vein margins in olivine. Wadsleyite is evidence of shock metamorphism in Nakhla, whereas the veins result from the decompression after the shock wave passed through due to impact(s). The identification of these secondary minerals constrains the temperature, pH, and redox conditions during the aqueous alteration, underlying that these conditions changed over time. For example, hisingerite forms at T = 120–140°C and ferripyrophyllite at 55–65°C, confirming a progressive temperature decrease when the alteration went forward. The occurrence of these Fe-rich phyllosilicates has also implications on possible past life on Mars: H2-fueled life cannot survive at T > 122°C; thus, it is incompatible with the formation of hisingerite. Life could have been possible only during the last step of aqueous alteration, that is, when the temperature decreased and ferripyrophyllite formed.