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Executive Summary

Executive Summary of NAI Team

BioMARS
July 1, 2006 – June 30, 2007

Introduction

The objective of the UC Berkeley-led BioMARS team is to integrate information about the coupled hydrologic, geomorphic and tectonic evolution of Mars and its mineralogic and geochemical composition with geomicrobiological data from Earth analog ecosystems to support the scientific framework for the search for evidence of past or current life on Mars. Our research on the evolution of Mars has been used to constrain its prior and current habitability and identify target environments for terrestrial analog studies. Analysis of Earth microbial systems has been undertaken to provide insights into the types of organisms and communities that could colonize these potentially habitable regions of Mars, their ranges of environmental tolerance, mechanisms of adaptation, and to define features of their possible biomarker or biosignature record. In the past year, our team’s research has included studies of: 1) the structure, composition, and evolution of Mars and its hydrosphere and atmosphere, 2) analysis of the past and current distribution of water at the surface, 3) exploration of processes that may have shaped the surface topography of Mars, 4) analysis of likely surface mineralogy and geochemical characteristics, and 5) comprehensive and focused investigations of several potentially relevant iron- and sulfur-based microbial ecosystems. Our studies, employing field, laboratory and modeling methods have revealed new mechanisms important to understanding Mars history and its possible habitability.

Structural and thermal evolution: implications for the Mars hydrosphere, surface, and atmosphere

The thermal history of a planet’s interior affects the hydrosphere and the release of volatile elements to the atmosphere. We have created a series of 1D numerical models to determine which classes of evolutionary models for the Martian interior can explain the history of crustal thickness, magnetic field, magma flux, and elastic plate thickness. We have found that a layered mantle, specifically a dense layer in the deep mantle, would lead to the generation of plumes and melting late in the planet’s history. This provides a mechanism for late stage volcanism, and, importantly the surface release of water. Numerical models for hydrothermal circulation near magma intrusions show that large amounts of water can be forced to circulate through the shallow crust without significantly affecting the subsurface temperature distribution. Our modeling efforts have also revealed that progressive interior cooling of the planet can pressurize water in sub-cryosphere aquifers sufficiently to crack the cryosphere and cause large water eruption on the surface, a process that may have operated throughout Martian history. Together these three modeling studies reveal mechanisms for an active Martian interior and exterior throughout the planet’s history.

Our analog geomorphologic studies now strongly indicate that, despite widespread assumptions to the contrary, groundwater discharge does not cause seepage erosion in bedrock and cannot explain the characteristic amphitheater headed valleys cut into volcanic rocks on the Martian surface. In our Idaho field site, in particular, we developed and exploited an unprecedented U-Th-4He-3He isotopic method to simultaneously date the eruption age and subsequent erosion controlled exposure age of lava flows. Our dates, coupled with detailed field mapping, demonstrate that the amphitheater headed canyon, long considered to be due to seepage erosion into the underlying basalt flows, was caused a one or more large flood events in the late Pleistocene. We also reject a seepage mechanism for large canyons on Hawaii and propose, instead, a new geomorphic erosion law to describe the process of canyon head formation by waterfall retreat due to vertically drilling of pools by gravel that tumbles down the falls.

There has been considerable debate about the occurrence and extent of ancient oceans on Mars. Although topographic profiles along possible paleoshorelines do not follow surfaces of equal gravitational potential, we now show that change in the orientation of Mars’ rotation axis in response to a large redistribution of mass can explain shoreline deformation, supporting the conclusion that there were once extensive and persistent bodies of water on Mars. In contrast to prior work, findings suggest that this ocean may have been centered in the tropics rather than the north polar region (Figure 1).

Finally, a key issue on Mars is the development of its atmosphere. Our experiments have shown that organic aerosols are likely to have been prevalent in the early atmospheres of both Mars and Earth. These aerosols, producing a photochemical haze, would significantly influence surface temperatures and the persistent liquid water at the planetary surface.

Microorganisms and their communities: membership, organization, and activity

Given the existence of persistent water at the Martian surface, we have continued analyses terrestrial microbial ecosystems dominated by the biogeochemical cycling of iron and sulfur. Our research has targeted microbial consortia associated with: 1) wet basaltic rock, 2) subsurface and surface neutral pH but microaerophilic solutions containing dissolved ferrous iron, 3) deep subsurface volcanic habitats with high concentrations of metal sulfide minerals, 4) active spring systems, and 5) hypersaline environments that may be partially analogous to ocean environments on Mars as surface water disappeared. The primary objectives of this work are to investigate how these environments are colonized, where colonization can occur, how adaptation to environmental extremes is achieved, and to identify potential biomarkers. We have documented the membership, and in some cases activity, of microbial communities sustained by iron oxidation and/or iron reduction in subsurface surfuric acid solutions associated with volcanic hosted metal sulfide deposits, basaltic rock, hypersaline spring and sedimentary environments, redox gradients in circumneutral pH solutions, and in hydrothermal systems. In addition, we have investigatged communities that participate in sulfur cycling in hydrothermal systems, hypersaline lake environments, and springs. Important findings include the discovery of: 1) the close association of iron oxidizers and reducers with basaltic rock outcrops at a site of groundwater discharge, 2) determination of the oxygen concentrations suitable for growth of neutrophilic iron-oxidizing bacteria and measurement of the kinetics of this metabolism, 3) the coupling of mat-based primary productivity in hypersaline environments with overlying carbon cycling and underlying carbon, iron, and sulfur cycling, 5) variation in diversity structure of communities associated with sulfide concentrations in active springs, and 6) documentation and genomic analysis of novel archaeal lineages within layered biofilm communities at low pH. Ongoing community genomics-based research aims to uncover the molecular mechanisms by which microorganisms and their communities adapt to high salinity and respond to environmental perturbation.

Biosignatures

Microorganisms both produce and dissolve minerals, leaving biosignatures indicating their prior activity. Recently, we have discovered a potential mineralogical biosignature in the form of nanoparticulate magnetite formed from maghemite by basalt-associated iron-reducing bacteria. We have also documented the role of proteins in driving aggregation of nanoparticulate sulfide mineral byproducts of sulfate-reducing bacteria and shown that proteins can be encased (and possibly preserved over long time periods) within the pores of resulting micron-scale aggregates (Figure 2).

An important goal has been to begin to integrate cultivation-independent bacterial-archael genomics studies with lipid studies so as to expand our understanding of how the ability to biosynthesize signature organic biomarkers (specific lipids and pigment molecules found in ancient rocks) is distributed across the tree of life. We have initiated a study of microbial communities in hyperaline solutions and biofilms that includes simultaneously sampling of community lipid plus pigment molecules and their DNA. The objective is to correlate known and new biomarker compounds with uncultivated and uncharacterized organisms, based in part on identification of biosynthetic pathways in community (meta)genomic sequence data. These findings will be used in an ongoing study of biofilm diagenesis in hypersaline lake sediments and studies of proterozoic rocks that aim to reconstruct the microbial ecology based on detection of diagnostic biomaker compounds.

Robot-based geomicrobiology

We are developing methods for robot-based geomicrobiology, as the exploration of Mars will be largely achieved robotically. We have constructed new robust, modular, reconfigurable robots better suited to the terrains that may be encountered. Primarily this involves adding rotational leg modules, which allow the robots to traverse larger obstacles. In the past year we began robot-based geomicrobiology field work using prototypes designed for surface geochemical measurements and sediment coring. Given that unexpected conditions may be encountered, we have also established alogrithms for robot reconfiguration mid-mission. The robots were deployed in a hypersaline lake site where other geomicrobiological studies are ongoing.

Education and public outreach

The BioMARS education and public outreach (EPO) effort aims to contribute to improvement in teaching and learning of science locally and nationally. The team has continued to develop instructional materials and approaches that emphasize an evidence-based approach to science education that is designed to enhance understanding of fundamental science concepts among teachers, students, and the public at large. We have developed and field-tested instructional materials for teacher training, created a new multi-media product that shows the growth of iron-oxidizing bacteria (subjects of ongoing team research), and generated complementary materials for use with the general public and field-tested materials in school and after school settings. We are currently developing a program for public participation in metagenomics-based science, focused around the Lake Tyrrell research site. The project aims to engage students and the public in science by sharing with them the excitement of discoveries made possible by access to new sequence information.