2011 Annual Science Report
NASA Ames Research Center Reporting | SEP 2010 – AUG 2011
Mineralogical Traces of Early Habitable Environments
The goal of our work is to discern the habitability (potential to support life) of ancient Martian environments, with an emphasis on understanding which environments could have supported more life than others. This information will help to guide the selection of sites on the Martian surface, for future missions designed to seek direct evidence of life. Our approach has two main parts: 1. We will use the presence of specific minerals or groups of minerals – an analysis that can be performed robotically on Mars — to constrain the chemical and physical conditions of the ancient environments in which they formed. 2. We will characterize the distribution of life on Earth in a series of environments spanning those same parameters, in order to inform the first portion of the investigation.
Our activities were strongly focused on field operations at the McLaughlin Natural Reserve. McLaughlin offers an important venue for understanding the biological potential of serpentinizing systems, in two regards. First, the site differs from many previously studied examples of serpentinizing systems in several respects, and therefore contributes diversity to the set of environments in which we can understand the relationship between biology and serpentinized rocks/fluids. Second, the site offers a unique opportunity to access subsurface communities through drilling and time-resolved down-hole experimentation.
We conducted a series of site-assessment field trips to McLaughlin to characterize the chemistry, microbial community structure, and metabolic activity of waters collected from a suite of existing wells sunk into serpentinizing ground. Early results show waters of clearly serpentinized character (high pH and low dissolved inorganic carbon), but with considerably lower dissolved H2 content than most studied sites. Microbial community structure is superficially comparable to that observed in spring effluents from several other, geographically diverse serpentinizing systems. Active biological consumption of both H2 and CO was documented, in waters having pH up to 11.5.
Subsequently, and with support from a NAI DDF award to Dawn Cardace, we undertook a two-week drilling project to collect cores and establish wells at a variety of depths and targeted sites, within the McLaughlin reserve. One core was retrieved from each of two sites, to depths of 125-150 feet, and a series of satellite wells (no core retrieval) were sunk adjacent to the primary holes, at depths determined to be of interest based on preliminary core analysis. These wells tap a variety of horizons indicative of serpentinizing conditions, including pH up to 11.7 and super-saturated methane. Along with core archival, depth-resolved samples were collected for analysis of microbial community structure (DNA and cDNA libraries, and metagenomic content), organic geochemistry, and mineralogy. The established wells will be monitored in time course for aqueous chemistry, and will be used for down-hole deployment of microbial growth experiments. Initial experiments (using methodology identical to that described for the established wells) did not show biological consumption of H2 or CO, possibly commensurate with the limited energy available in these metabolisms in the horizons accessed by drilling.
We also utilized samples collected from our Josephine Ophiolite locale to conduct comparative analyzes using instruments comparable to the ChemCam and CheMin MSL instruments, as a means of informing Mars surface operations by ground-truthing against well-studied terrestrial locales. Finally, we field deployed a prototype of a hybrid Moessbauer-XRD instrument at our Hawaiian field site. The prototype is intended for development as a sample screening instrument (screening-level assessment of habitability from mineralogy) for use on future Mars missions.
PROJECT INVESTIGATORS:Tori Hoehler
PROJECT MEMBERS:David Blake
RELATED OBJECTIVES:Objective 2.1
Biochemical adaptation to extreme environments