2013 Annual Science Report
NASA Ames Research Center Reporting | SEP 2012 – AUG 2013
Mineralogical Traces of Early Habitable Environments
The goal of our work is to understand how habitability (potential to support life) varies across a range of physical and chemical parameters, in order to support a long term goal of characterizing habitability of environments on Mars.
The project consists of two main components:
1. We are examining the interplay between physicochemical environment and associated microbial communities in a subsurface environment dominated by serpentinization (a reaction involving water and crustal rocks, which indicated by surface mineralogy to have occurred on ancient Mars).
2. We are working to understand how mineral assemblages can serve as a lasting record of prior environmental conditions, and therefore as indicators of prior habitability. This component directly supports the interpretation of mineralogy data obtained by the CheMin instrument on the Mars Science Laboratory.
Efforts during the performance period were focused in two main areas:
Samples for aqueous geochemistry and molecular biology were collected and analyzed quarterly from the borehole observatories established in 2011, as part of a well recovery and seasonal monitoring campaign. We also established an initial suite of microbial colonization experiments within the boreholes. To our knowledge, this is the first suite of time-resolved down-hole colonization experiments to have been deployed in actively serpentinizing subsurface. A first round of post-deployment monitoring has been conducted, with results presented in several 2013 AGU abstracts and in prep for submission. An extensive metagenomic and pyrotag sequencing analysis of fluids and solid material from the new wells was conducted and compared against in situ metabolic activity assays. Initial results demonstrate that, when arrayed against a series of other serpentinizing systems, the highest-pH CROMO wells have the lowest genetic diversity yet observed. The high pH samples also demonstrate very low to unmeasurable metabolic consumption of hydrogen and CO, suggesting that our sites span a gradient that may encompass marginally or uninhabitable conditions. Finally, our method for clean drilling (which utilized steam-sterilized drill bits and purified drinking water as drill fluid) and contamination monitoring (introduction of microbe-sized fluorescent spheres into the drill fluid) was published in Scientific Drilling.
In parallel, we worked to develop a numerical model that determines the supply and demand of metabolic energy as a function of fluid composition, and ultimately as a function of host rock composition. The model is applied to demonstrate the range in habitability across a range of serpentinizing fluid chemistries, including those at CROMO, and across the hypothetical chemical space represented by the range of naturally-occurring ultramafic rock compositions. Two manuscripts are currently in preparation based on these efforts. We also published a paper in Nature Reviews Microbiology that surveys the current understanding of microbial life in very low energy surroundings – a conceptual link between the CROMO field work, the modeling effort, and attempts to understand the biological potential of the subsurface on Mars, Europa, and other bodies that might offer habitable subsurface niches.
Team members Blake, Des Marais, Morris, and Treiman were heavily engaged in surface operations of the Mars Science Laboratory, as part of the CheMin (X-ray diffraction) instrument team. The team performed the first ever X-ray diffraction analysis on the surface of another world. Comparative mineralogical analysis, as partially informed by analysis of mineral alteration samples collected during the early phase of our project, was a critical component of the assessment of prior habitable conditions at the “Yellowknife Bay” site. Results of these efforts were published in Science, as part of the first round of MSL science papers.
PROJECT INVESTIGATORS:Tori Hoehler
PROJECT MEMBERS:David Blake
RELATED OBJECTIVES:Objective 2.1
Biochemical adaptation to extreme environments