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Cold and wet early Mars: Proposing and testing a new theory to understand the early Martian environments

Final Report Summary - ICYMARS (Cold and wet early Mars: Proposing and testing a new theory to understand the early Martian environments)

Background:
The “icyMARS” project aimed for a paradigmatic shift towards the understanding of the evolution of early Mars, defining and testing a new hypothesis: that the Martian environment was characterized by global mean freezing conditions, as predicted by climate models, and at the same time a vigorous hydrogeological cycle was active during hundreds of millions of years, as confirmed by geomorphological and mineralogical analyses: a “cold and wet” early Mars. For this purpose, “icyMARS” followed an ambitious interdisciplinary approach, working on four interconnected Themes: (1) the geomorphological characterization of ancient glacial and periglacial features; (2) geochemical studies on Martian aqueous mineralogy at subzero temperatures; (3) the understanding of the link between the global climate change on early Mars and the mineral transition from hydrated silicate- to sulfate-dominated sediments; and (4) the habitability of cold aqueous solutions, brines and hygroscopic salts on Mars.

Achievements:
(1) We have published groundbreaking advances (not just incremental science) in Theme 1, concerning the geomorphological characterization of a cold early Mars. In the light of the recent advances by landed missions, the obvious site choice for our work was Gale crater, the most carefully analyzed place on Mars to date. By effectively characterizing the geomorphology of Gale using a combination of large-scale (orbital) to detailed (rover) datasets, we demonstrated that Gale’s geomorphological record preserves the clues to understand the environmental transitions on a “cold and wet” early Mars. Our Team pioneered the consideration of Gale as an ancient glacial and periglacial landscape. We have extended our geomorphological investigations about water/ice interactions on the Martian landscape, and have published our results on the following items: (i) we discovered evidence for tsunami activity reshaping the ice-covered Hesperian littoral landforms, (ii) analyzed periglacial landforms in Argyre, (iii) tied the origin and evolution of the circum-Chryse outflow channels to freeze-thaw processes during and after the Hesperian, and (iv) presented evidence for an episode of extensive polar plateau retreat in the South Polar layered deposits during the Late Amazonian.
(2) Regarding Theme 2, we have published new geochemical models focused on the process of melting/freezing of ionic solutions or brines at and below 273K, and the role of the enthalpy of phase transition in this process. Innovative published outcomes include the analysis of multiple eutectic and/or peritectic points in binary and multicomponent systems of enantiotropic substances (i.e. the different phases of Mg-sulfate), and descriptions of the enhanced overfreezing effect due to the continuous increasing of the ionic strength in systems undergoing evaporation. We also investigated long-term oxidation processes taking place in anoxic environments, as those occurred during the weathering of primary minerals in early Mars. Our results suggest that pyrite dissolution can act as a natural Fenton reagent, influencing the oxidation of third-party species during the long–term evolution of geochemical systems, even in the early Mars oxygen-limited environments. In addition, we have developed and published models to describe the paths of Li isotopic fractionation on Mars, as Li isotopic ratios can inform about weathering conditions on Mars in the past, including the extent of basalt weathering, supersaturation and evaporation rates of initial solutions, and ambient temperature. This is very timely because NASA’s Mars2020 rover will be capable of performing in situ measurements of Li isotopes on Martian alteration products, and there are ongoing [Li] measurements by MSL/Curiosity.
(3) Theme 3 has resulted in three major achievements in Mars mineralogy. Our aim was to understand the sedimentary mineralogy on Mars, where mineral sequences show that salts generally do not appear together with clays. First, “icyMARS” tackled this problem by assuming that the driving factor separating the different mineralogies was temperature (climate change). To our surprise, we have discovered that the synthesis of clays vs sulfates on Mars was initially controlled by the reactive surface of primary minerals. This was totally unexpected and is one of the major outcomes of “icyMARS”. Second, we have kinetically modeled the stability boundaries for the synthesis of sulfates and phyllosilicates. Also unexpectedly, under some conditions our results are consistent with a contemporary formation of all major water-derived mineralogies in different aqueous environments during the wet Noachian/Hesperian times, revealing an active and heterogeneous early Mars. And third, as cold liquid water is not warm enough for surface clays to form, we realized that understanding the formation conditions of martian clays will result in a better understanding of the early martian climate. Our results have shown that short-term warmer environments, occurring sporadically in a generally cold and wet early Mars, better enabled formation of the observed surface clays on Mars. Theme 3 has come far, and the results are actually well beyond expectations.
(4) In the fourth Theme, we developed several new concepts related to the potential of low-water activity solutions and brines that existed on early Mars to support growth and/or survivability of Martian analogue extremophiles, with the aim of fingerprinting putative paths of microbial adaptation on a “cold and wet” early Mars. We studied the geochemical evolution of water ponds in the Atacama desert (Chile) as potential astrobiological analogues for habitable environments on Mars, and our work resulted in several publications dealing with the first identification of the deleterious effect of rains on the super-specialized bacterial communities inhabiting the hyperdry Mars-analog Atacama soils, the first identification of microbial communities in the wet subsurface clays less than 1 m deep in the desert, and the first analysis of wind-transported microbes all through the desert. In addition, we published the innovative proposal of considering the Argyre basin as a candidate site for in situ astrobiological reconnaissance, particularly those landscape features and terrain types associated with the migration of water/ice/brines along Argyre’s structures and the venting of volatiles.

In perspective:
Research from “icyMARS” has produced a large number of innovative results in different fields (geomorphology, geochemistry, mineralogy, astrobiology), well beyond the initial objectives of the project. Our research has significantly advanced the state of the art, leading to a large number of peer-reviewed publications, meeting communications and press releases. Importantly, our pioneering concept of a “cold and wet” early Mars has been already embraced by several other research groups dealing with the conundrum of the early Mars environment. As a consequence, our new “cold and wet” paradigm for early Mars is now widely acknowledged and is being further developed by the community.