Check out our AGU Session for December '18: "The New Mars Underground" https://agu.confex.com/agu/fm18/prelim.cgi/Session/51671 Check out our new efforts to enable Mars Subsurface Exploration—searching for signs of life on Mars and for resources that would enable human presence. And check out our white paper on Mars Deep access.
Why Mars subsurface?
Access to the Martian subsurface offers an unprecedented opportunity to search for the “holy grail” of astrobiology—evidence of extinct and possibly even extant life on Mars—a journey started by the Viking landers more than four decades ago. Analyzed samples would also deliver the puzzle pieces needed to help complete our understanding of how the Martian climate, its carbonates, and its volatile inventories changed over time and may have impacted, or may have been impacted by, life.
Evidence from orbiters and rovers suggests a once “warmer and wetter” Mars [e.g., Grotzinger & Milliken, 2012] and recent results from the MAVEN mission demonstrated that a significant fraction of the Martian atmosphere was lost early in the planet’s history [Jakosky et al., 2017]. As its atmosphere thinned, the flux of harmful radiation reaching the Martian surface would have increased and the surface temperatures would have cooled well below the freezing point of water. Consequently, the cryosphere would have thickened and stable groundwater would have moved to greater depths below the surface. Therefore, if Mars ever had life (regardless whether it emerged on or below the surface), then it should have followed the permafrost/groundwater interface to progressively greater depths where stable liquid water can exist. There, shielded from seasonal and diurnal temperature effects as well as from harmful effects of ionizing radiation, it could have been sustained by hydrothermal activity, radiolysis, and rock/water reactions. Hence, the subsurface represents the longest-lived habitable environment on Mars. Therefore, in comparison to the surface, our chances of finding signs of extinct life are much greater in deep, protected, self-sustaining subsurface habitats that putative organisms might have inhabited [e.g., Michalski et al., 2017].
If extant life exists on Mars today, then the most likely place to find evidence of it is at depths of a few hundred meters to many kilometers, where groundwater could persist despite today’s low geothermal gradients [Clifford et al., 2010; Grimm et al., 2017]. Moreover, while the preservation of molecular biosignatures on Mars is debated, the consensus is that detection at depths greater than a few meters is favored because of the shielding from harmful radiation [e.g., Kminek and Bada, 2006; Pavlov et al., 2016].
Additionally, accessing information in the Marian subsurface (geochemical, geophysical, and astrobiological) to obtain subsurface profiles of the D/H, 18O/16O, carbonate content, organics, pH, volatiles, redox conditions, porosity, permeability, temperature, and stratigraphy—unaffected by atmospheric processes or solar/cosmic radiation—will enable us to much better constrain the environment for life over geological timescales, i.e., the time-dependent variation of water loss, climate, volcanism, and tectonic processes.
Therefore, the exploration of the full potential of extinct or extant life on Mars and its environmental context over the last few billion years requires accessing the deep subsurface, and the collection of samples—starting a few meters below the surface but ideally reaching the putative modern day stable water table at hundreds of meters to kilometers depth.
We now have the capability to achieve this goal, specifically due to (a) recent technological advances, (b) an improved understanding of the local variability of Martian environments, and (c) increasing commercial, international, and human opportunities on Mars:
- technological advancements in miniaturization, automation, data processing, sensor-driven adaptation, fault protection and recovery, and instrumentation for chemical characterization of soluble, gaseous, and solid compounds can make in situ deep subsurface exploration and wide high resolution subsurface sounding for volatiles down to a few km of depth feasible,
- latest scientific results on the 3D diversity of Martian surface and, increasingly, subsurface environments facilitate more rigorous landing site selection and the correlation of local results within a global context, and,
- emerging commercial, international, and human opportunities on Mars enable out-of-the box approaches: commercial collaboration opportunities through, e.g., SpaceX, could provide flights to Mars every 2 years, possibly as early as 2022; growing international interest in Mars exploration by the Emirates, India, China, and Japan in the early 2020s can broaden international collaborations; and NASA’s & SpaceX’s plans of sending humans to Mars in the 2030s call for mapping Martian resources and the astrobiological potential of the subsurface.
Check out our 2018 white paper on Mars Deep access.