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Habitability of Martian Environments: Exploring the Physiological and Environmental Limits of Life

Final Report Summary - HOME (Habitability of Martian Environments: Exploring the Physiological and Environmental Limits of Life)

We assembled a highly effective research team achieving the goals set forth in the HOME (Habitability of Martian Environments) project. This included a huge consortium of European and non-European investigators for the analysis of a wide variety of biological, geological, chemical, and environmental parameters in one of the most challenging environments on our planet, the hyperarid core of the Atacama Desert, to determine the dry limit of life on Earth and Mars. In fact, this was the largest consortium with the broadest expertise that to date has undertaken research in this driest non-polar desert of Earth, which is one of the best analog sites to understand chemical, physical, and possible biological processes on Mars. The previous paradigm was that microbes are blown in by wind and slowly dying in this extreme environment. However, we showed, by using state-of-the-art technology, including metagenomics and external and internal DNA and ATP analyses that microbes are still actively growing and reproducing, using the desert as a habitat (published in PNAS). We also found that the most extreme outpost of life in the Atacama are salt rocks, in which endolithic bacteria thrive using the process of deliquescence to provide them with life-sustaining water. This led us to the insight that when searching for life on Mars we should not follow the traditional NASA paradigm to follow the water, but to follow the salt, because hygroscopic salts allow microbes to draw the essential water directly from the atmosphere. We put this idea forward at various international scientific meetings such as the 2019 NASA “Extant Life on Mars” Workshop.
We also developed a novel lab set-up to test whether microbes can thrive on deliquescence only as a source of water. We found that certain methanogenic archaea can do so, which is directly relevant to Recurring Slope Lineae on Mars, thought to be seasonal salty water flows, as a potential habitat of life. More importantly, our findings can explain the puzzling presence of methane in the Martian atmosphere as a possible biological process. Realizing the importance of salt for microbes in Mars-like conditions, we also tested the resistance of life to salt solutions, particular to perchlorates, which are common on Mars. By doing so we set new records for microbes dealing with high concentrations of sodium perchlorate, extending with our research the parameter space limiting the habitability of such an environment. In addition, we exposed microbes under Mars-simulated conditions on the International Space Station and tested soils and microbes in a specialized Mars Simulation Chamber, showing that cyanobacteria can still metabolize under certain near-surface environmental niche conditions. Our conclusion must be that microbes are much more hardy than previously thought and can survive, and likely thrive, under environmental conditions that occur at specific locations and times on Mars.
One challenging but also rewarding aspect of our research has been the development of an instrument to detect life on Mars. While the original approach proved to be non-working due to the challenge of utilizing a sterilization method (for control) without changing the soil matrix, we succeeded in developing a detection method using the motility of microbial life. Microbes have specific movement patterns that can be identified and tracked using an algorithm. Because these movement patterns are so different from random movement, we succeeded to show that certain types of microbes can be identified, including pathogens, which is not only relevant for the search of life on Mars, but has also many other applications.
The HOME team has been extremely active in both presenting at conferences and publishing papers, a total of 30 in the project period, many of them in high-impact journals. It speaks of our interdisciplinary team and our team effort that our work involves so many colleagues from other institutions, all of which contributed to our effort with their time and resources.