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Suggestions for Future Research

The review committee’s statement of task (see Preface) did not call for recommendations for future research to reduce uncertainties surrounding the various issues and questions discussed in its report. Nevertheless, the committee was verbally encouraged to do so by the planetary protection officers from NASA and ESA. In the absence of a formal request for specific research recommendations, the review committee has limited itself to providing suggestions for future research. These suggestions are open ended and are not comprehensive. They are not directed at any particular organization or group and are unlikely to provide new insights or information on a timescale that will impact the Mars missions currently in development. Moreover, since they were not formally requested, they are not developed in any detail and contain few, if any, specifics. Nevertheless, the review committee believes that they represent a good starting point for any future group chartered to study Special Regions and issue formal recommendations.

It will be noted that the research directions identified below cover topics of interest to astrobiologists, planetary scientists, and planetary protection practitioners. The casual reader may ask where do astrobiology or planetary science end and planetary protection begin. The review committee does not recognize these disciplinary distinctions: at best they are just different approaches to addressing fundamental questions—such as, are we alone in the universe—in a scientifically responsible manner. In that spirit, we propose the following suggestions for future research in order to shed light on issues identified during the review process:

Investigations of the Limits of Life on Earth

• Undertake standardized laboratory investigations with microbial communities to analyze their responses to environmental stressors in general. Examples include the effects of low temperatures, temperature cycles around the freezing point, low pressure, Mars-like atmosphere, low water activity, periods of complete desiccation, oligotrophic nutrient media, periods of starvation, exposure to ionizing radiation, and exposure to Mars-like polychromatic ultraviolet radiation.
• Undertake long-term investigations of psychrophilic microbial isolates and psychrophilic microbial communities to determine the lower temperature and water-activity limit for replication and analyze the effect of chaotropic compounds on these limits.

• Investigate the potential capability of microbial isolates and microbial communities to divide if water is only present in the form of water vapor over the full temperature range for which microorganisms are known to replicate.
• Investigate the potential of microbial isolates and microbial communities to use liquid water in thin films on mineral grains as their sole source of water for replication.

Life in Extreme Environments and in Multispecies Communities

• Investigate the effects of successively and simultaneously applied multiple Mars-relevant environmental stress factors on microbial isolates and microbial communities to improve understanding of the mechanisms of adaptation, the evolutionary process whereby an organism becomes better able to live in habitats subject to extreme environmental conditions.
• Undertake experiments to determine the minimum threshold of microbial isolates and microbial communities found in spacecraft assembly facilities and on spacecraft that can establish a community in a simulated Mars Special Region.
• Undertake in situ mapping of the microheterogeneity of biologically important environmental parameters in the landing ellipse of a future space mission dedicated to astrobiology.
• Understand the role and selective advantage of the biofilm form of life in more depth, with emphasis on the tolerance to Mars-relevant stressors (e.g., desiccating conditions, low water availability, low temperature, high fluences of biologically effective ultraviolet radiation, ionizing radiation.

Detectability of Potential Small-Scale Microbial Habitats

• Perform in situ investigations in extreme environments on Earth to deepen our knowledge about microbial processes and habitability at micron scales. Adapt and optimize existing technologies and develop new ones to undertake the kind of investigations which may be used in the future exploratory missions to other planets and moons of astrobiological relevance.

Translocation of Terrestrial Contamination

• Undertake investigations of transport mechanisms and microbial viability in Mars simulation chambers—e.g., the Mars Surface Wind Tunnel facility at NASA’s Ames Research Center or the low-pressure recirculating wind tunnels in the Mars Simulation Laboratory at Aarhus University—wherein microbes and spores are exposed to Mars-relevant levels of ultraviolet radiation, desiccation, nutrient deficit, and air movement, to assess the likelihood of survival during transport by, for example, dust storms.

Methane: Potential Abiotic and Biotic Sources

• Study the possible source and/or reservoirs of active methane release on Mars to identify the mechanism(s) responsible for producing and/or releasing it to the martian atmosphere. The ExoMars Trace Gas Orbiter could potentially acquire data that are essential to address this problem.

Dark Slope Streaks and RSL

• Study the formation of RSL and the class of dark slope streaks that shares similarities to RSL. It would be especially important to devise laboratory experiments and better tests of the “dry” and “wet” hypothesis for the formation of these features.

Polar Dark Dune Streaks

• Research to address the formation of liquid brines and segregated ice in the polar regions. It would be particularly important to conduct laboratory experiments to study these processes.

Shallow Subsurface Conditions and Ice Deposits

• Studies to address the formation of liquid brines on past and future landing sites, the kinetic factors involved, and their implication for microbial growth.

Snow, Ice Deposits, and Subsurface Ice

• Research addressing the range of conditions in which liquid brines could form and be temporarily stable on the surface and shallow subsurface of Mars.

Human Spaceflight

• Conduct research and related activities to understand the implications of landing and operating human systems on Mars in a manner consistent with COSPAR planetary protection policy.

Additional Considerations

• Research to develop new bioburden assays for microbes with a high probability to survive in the martian environment. Assays taking into account the latest detection technologies and the specific requirements, restrictions, and practicalities imposed by the assembly, integration, and testing of space hardware are required.