2013 Annual Science Report

Arizona State University Reporting  |  SEP 2012 – AUG 2013

Habitability of Water-Rich Environments, Task 4: Evaluate the Habitability of Ancient Aqueous Solutions on Mars

Project Summary

Co-I Farmer explored for past habitable environments on Mars as part of the MSL (Curiosity) team. He also participated in efforts to develop new life detection instruments for in situ astro-biological exploration of Mars, and documented lipid bio-signature preservation in siliceous hydrothermal deposits.

Co-I Zolotov developed chemical weathering models for Mars. He argued that formation of salts and phyllo-silicates in the Noachian epoch was followed by aqueous mobilization and deposition of neutral salts in the Hesperian epoch. This hypothesis implies the occurrence of sulfate-saturated subsurface waters during a prolonged time after the formation of phyllo-silicates.

4 Institutions
3 Teams
4 Publications
0 Field Sites
Field Sites

Project Progress

In 2013, as a member of the MSL Science team, Prof. Farmer actively supported surface operations of the Mars Science Laboratory rover Curiosity via remote operations from ASU. This involved planning observations, acting as Payload Downlink lead and participating in science discussions. As the Education and Public Outreach POC for the MSL CheMin team, he helped organize and lead a five-day, field-based teacher training activity on Mars habitability In June, 2013. Prof. Farmer also completed the initial phases of a collaborative fossil bio-signature study using laser Raman methods for organic matter detection in a variety of aqueous lithologies regarded to be important Mars analogs. Working with laser Raman expert, Jordana Blacksberg (JPL), the work seeks to define new technological and operational approaches for reducing fluorescence in rock samples, to aid the in situ identification of kerogen; this information will be used to design a new generation of Raman instruments for flight. This work involves graduate student participation supported by a one-year JPL SURP grant.

Discoveries by the MSL Curiosity team of water-deposited conglomerates on Bradbury Rise, along with clay minerals at Yellowknife Bay (both reported in Science), have provided consistent evidence for past aqueous processes and environments at Gale Crater, Mars, with potential habitable environments in the past. Furthermore, mineralogical evidence suggests solutions had a circum-neutral pH and a low salinity. Farmer and his MSL team collaborators are continuing their exploration for ancient habitable zones, as they drive toward the base of Mt. Sharp, a thick sequence of layered sedimentary rocks, three times thicker than the Grand Canyon sequence.

In 2013, Prof. Farmer also continued collaborations with Linda Jahnke (NASA Ames, Exobiology Branch) and her colleagues, writing up results of field and lab studies documenting lipid bio-signature preservation in siliceous hydrothermal spring sinters, over a broad range of pH and temperature.

Mikhail Zolotov, Co-I has developed numerical models for chemical weathering of Martian basalts through percolation of aqueous solutions from above. Neutral and acidic solutions have been tested. The modeled weathering profiles were compared with observations and a good match was observed for acidic models (Refer to Figure 1). It was shown that water-soluble salts are unavoidable products of acidic weathering that leads to formation of observed phyllo-silicates. The formation of phyllo-silicates together with salts suggests a formation of abundant salts in the Noachian epoch. Neutralized fluids rich in high-solubility Mg and Na sulfates and chlorides could have accumulated in ground waters. In the Hesperian epoch, subsurface drainage of neutral fluids into depressions (Valles Marineris and other chasmata) could have been followed by the formation and evaporation of sulfate-rich lakes. This scenario explains the predominant occurrence of phyllo-silicates in Noachian deposits and appearances of massive sulfate deposits in younger Hesperian depressions. These models provide new insights into the nature of subsurface habitable environments during a prolonged period after the formation of phyllo-silicates.

Figure 1. The water-rock (W/R) ratio as a proxy for depth in a weathering profile of martian basalt. Upper layers are altered at higher W/R ratios. Kaolinite, montmorillonite, and amorphous silica form at high W/R ratios. Fe-Mg clays are abundant at lower W/R ratios (at depth). The results agree with observations in the Mawrth Vallis region and predict minerals which have not been observed.