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The physicochemical nature of water on early Mars

Periodic Reporting for period 1 - MarsFirstWater (The physicochemical nature of water on early Mars)

Reporting period: 2019-06-01 to 2020-11-30

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. Between 4.5 and 3.5 Gyr ago, Mars is thought to have had an active surface hydrosphere that included glaciers, rivers, (ice-covered) lakes, deltas, and maybe even a hemispheric ocean. 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. Most of the tasks proposed and methodologies used have just reached the required level of maturity to be tackled, and therefore they represent frontier areas of research. The final goal of this proposed investigation will be testing current hypotheses and developing alternative overarching processes and descriptive models, producing new knowledge beyond merely incremental advances. Very specific knowledge gaps have been and will be identified, and all key outcomes of this Project will address very precisely those identified gaps. The planned investigations will benefit from the combination of working with first-hand data from ongoing Mars missions and with the ultimate laboratory tools at the host institution. 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. In particular, this research will advance a new perspective about the evolution of planetary habitability that can feed the development of future missions, payload concepts, and novel instrumentation for exploring both Mars and Earth, also informing about challenging constraints for Planetary Protection policies in current planetary exploration.
The work is organized in 4 Research Themes (RTs). Major scientific developments in this period have included, in each RT:
• RT1, Geology: We have provided the first identification of rythmites on Mars, contributing to describe the properties of the ice-rich permafrost characterizing most of the Martian subsurface/surface interface, and the role of fluid dynamics on the morphology of the resulting fluvial features. This finding has prompted the reevaluation of our initial hypothesis that glaciovolcanic processes triggered valley network and lake formation on early Mars, because we have identified impact events as a major source for the triggering of liquid water on early Mars. We estimate a degree of completion of the objectives of this RT slightly over 25% in this first period.
• RT2, Geochemistry: We have quantified how past fluids 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 have started to quantify how and to what extent host-rock composition determined the geochemical evolution of hydrated mineral sequences on early Mars, identifying that sulphide (pyrite) and silicate minerals determined the redox evolution of early aqueous settings on Mars. We estimate a degree of completion of the objectives of this RT around 35% in this first period.
• RT3, Mineralogy: We have provided the first identification of glauconite minerals on Mars using in situ data from the rover Curiosity. This finding contributes to clarify how the formation of clays occurred on early Mars. Ascertaining the spectral and mineralogical properties of hydrated materials substantially helps their identification in spacecraft datasets. We estimate a degree of completion of the objectives of this RT slightly over 25% in this first period.
• RT4, Astrobiology: We have quantified the extent at which Earth’s microbial species could thrive in the low aw of the cold solutions and brines that existed on early Mars, studying microorganisms with the ability to change the freezing/melting curve of cold salty solutions by the expression of proteins that can affect the liquid-to-ice transition. 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 where to look for evidences of an ancient biosphere on Mars, and which biomarkers on Mars would be similar to those produced by microbial communities on Earth. We have contributed a new instrument concept to look for evidences of an ancient biosphere on Mars. We estimate a degree of completion of the objectives of this RT around 40% in this first period.
Most significant advances to date include (1) the first identification of rythmites on Mars using in situ rover data, (2) the first quantification of the effects of fluid pH on the capability of clays to preserve organics, (3) the first identification of glauconites on Mars using in situ rover data, and (4) the discovery of a wet clay subsoil in the Atacama Desert inhabited by dozens of different species of extremophiles.

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 explaining how sulfates can be formed by disulfide dissolution under a reducing atmosphere, without considering atmospheric oxidizing agents, therefore providing an alternative experimental justification for the oxidizing potential of Martian soils; (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 (4) finding and characterizing representative microbial model species in order to understand how life was able to adapt to the desiccation stress recorded in the Mars geological record, and how it may have evolved to remain metabolically active in the desiccated state.
RT3: Infrared spectra of clays containing organics before and after exposure to different pHs.
RT1: Schematic diagram showing the evolution of antidunes triggered by flash floods on Gale crater.
RT4: Mass chromatograms of the major lipid famiies found in the subsurface of the Atacama desert.
RT2: Grey, non-oxidized substrate shows up after scratching some mm under the red coating of Mars.