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The physicochemical nature of water on early Mars

Periodic Reporting for period 2 - MarsFirstWater (The physicochemical nature of water on early Mars)

Reporting period: 2020-12-01 to 2022-05-31

Mars is the only known planetary body, other than Earth, where liquid water appears to have played a key role in its early surface evolution. However, details regarding the physicochemical nature of water and its early evolution, on both global and local scales, whether liquid or solid H2O dominated, for what duration of time, when and where, what were the host-rock weathering rates and patterns and the physicochemical parameters defining such interactions, what specific landforms and mineralogies were generated during those periods, and what implications all these processes had on the possible development of life on Mars, are still poorly developed. Many fundamental questions about aqueous processes on early Mars are still in the need of answers.

The overall objective of this investigation is to fully characterize the physicochemical nature of water on early Mars through a quantitative and truly interdisciplinary investigation. Several innovative strategies in geomorphological analysis, geochemical modeling, mineralogical studies and astrobiological investigations will fill the existing gaps, producing hard constraints on the physicochemical nature of water on early Mars. This is a truly interdisciplinary Project: all the different lines of investigation are intimately interrelated among them, and results being produced as tasks evolve will feed other research areas in a continuous internal synergy.

The results of this investigation will prove a pathfinder for other investigators’ qualitative and quantitative analyses of Martian hydrogeology, geochemistry and mineralogy, computer modelling, microbiology, and robotic mission operations and data analysis, providing opportunities to opening new paths for in situ exploration by landers and rovers.
The work is organized in 4 Research Themes (RTs). Major scientific developments from the beginning of the project to the end of the second period (36 months) have included, in each RT:

• RT1, Geology: We have published a new geomorphological map of the Sinus Sabaeus region of Mars, providing a basis for identifying the ancient presence of water in the region, both in the liquid state and in the ice phase. We have provided the first identification of rythmites on Mars, meaning that impact events were a major source for the triggering of liquid water on early Mars. We have contributed the hypothesis that present-day humidity and temperature cycling at Gale crater is driving and actively cyclic expansion and contraction of mud-rich bedrock and sediment. We have reconstructed the formation process of Mars-analog inverted channels in the eastern Sahara during the African Humid Period, to decipher how fluvial systems responded to a wet to dry climate cycle on early Mars. And we have contributed a new strategic roadmap for planetary caves exploration, answering fundamental science and engineering questions for the robotic exploration of Mars.

• RT2, Geochemistry: We have quantified how past fluids on Mars interacted with and altered the surface, depending on fluid pH, and how this alteration modified the preservation potential of organic matter embedded in clay minerals. We investigated the recycling of phosphorous and its bioavailability in carbonate and iron-rich Archaean deposits on Earth, to expand our understanding of the possible origin of life on Mars. And we have identified the limits of sensitivity and biases of several biosignature-detection instruments that are on or will be soon sent to Mars, using testbed instruments on samples from a region of the Atacama Desert with extremely low concentrations of organics.

• RT3, Mineralogy: We have provided the first identification of glauconite minerals on Mars using in situ data from the Curiosity rover, contributing to clarify how the formation of clays occurred on early Mars. We have provided a detailed characterization of the nature and prevalence of carbonate minerals in the Nili Fossae area of Mars, with a particular focus in Jezero crater, the investigation site of the Perseverance rover. And we have provided the first identification of a subsoil wet clay layer in the hyperarid core of the Atacama Desert, harvesting new data to help determine the preferred mineral sequences where to look for biosignatures in the Martian subsurface.

• RT4, Geomicrobiology and Astrobiology: We have contributed a new instrument concept to look for evidences of an ancient biosphere on Mars. We have studied the potential ability of microorganisms to change the freezing/melting curve of cold salty solutions by the expression of proteins that can affect the liquid-to-ice transition on early Mars. And we investigated 3 Mars bioanalogs: (1) Tirez Lake, a desiccated endorheic hypersaline lagoon, to analyze the evolution of the microbial communities during desiccation; (2) Antarctica, to study the geomicrobiology of the permanently exposed lithic substrates of nunataks; and (3) the Atacama Desert, to better understand the dispersion of microbial life using dust transported by wind, and to search for subsurface life in the wet clays in the subsoil.
Most significant advances to date include (1) a novel mapping of water and water ice during the Noachian near the Martian dichotomy; (2) the first identification of rythmites on Mars; (3) the first quantification of the effects of fluid pH on the capability of clays to preserve organics; (4) the identification of sensitivity limits of biosignature-detection instruments landed on Mars; (5) the analysis of the bioavailability of phosphorous in carbonate and iron-rich deposits; (6) the first detection of glauconites on Mars; (7) the discovery of subsurface wet and inhabited clays in Atacama as analogs to the Martian subsoil; (8) the use of a novel methodology, µ-DSC, to identify a potential metabolic pathway by which microorganisms may increase the habitability of cold salty solutions on early Mars; (9) the first long-term analysis of the desiccation of an athalassohaline lagoon, Tirez lagoon, unveiling the response of the microbial communities to the desiccation stress; and (10) the proposal of a new astrobiological instrument to search for biomarkers on Mars and icy moons (our paper describing this instrument received the “EANA 2021 Outstanding Paper Award”).

The expected results until the end of the project include (1) determining the physical properties of the Martian cryosphere to enhance understanding of the global hydrological cycle for ancient Mars, the global water inventory for the planet, and the planet's geo-hydrological evolution through time; (2) quantitatively investigating the chemical nature and redox evolution of the primeval aqueous solutions on Mars, exploring how and to what extent host-rock composition determined the geochemical evolution of hydrated mineral sequences on early Mars; (3) advancing understanding of the evolution and modification of the Martian surface, in particular the inventory of volatiles in the Martian early silicate crust and how past fluids interacted with and altered the surface; and (4) finding and characterizing representative microbial model species and their environments, in order to understand how life was able to adapt to the desiccation stress (included by freezing).
RT3: The Atacama subsoil with wet inhabited clays.
RT1: Geomorphological map of Sinus Sabaeus
RT4: Sampling at Tirez.
RT2: Mars is grey scratching the surface just a few mm.