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Executive Summary

The objective of the UC Berkeley-led BioMARS team is to integrate information about aspects of 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.

The thermal history of a planet’s interior affects the hydrosphere and the release of volatile elements to the atmosphere. We are developing numerical models for hydrothermal circulation near magma intrusions in order to determine the volume and rate at which liquid water can be released at volcanic centers. Previous studies of the Martian interior have highlighted the difficulty in maintaining plumes throughout the history of the planet and predict a very brief existence of a magnetic field. We have created a series of models to explain the history of crustal thickness, magnetic field, magma flux, and elastic plate thickness that considers a layered mantle and the influence of plumes on melt generation. We find that a dense layer in the deep mantle provides a robust mechanism for the generation of plumes and melting late in the planet’s history.

The focus for hydrologic and geomorphologic studies is to evaluate evidence for sustained water at or near the surface of Mars. We have added a comparison with Titan channels to further test our theories. In order to search for the evidence of abundant near-surface liquid, we reinterpreted the run out distances of the numerous Amazonian landslides in Valles Marineris and find that the distance they traveled is best explained by models for dry landslides, implying the availability of limited amounts of liquid water. However, an empirical summary of earth-based responses to shaking caused by earthquakes suggests that Mars quakes could release large amounts of liquid over wide areas fairly frequently.

Our original premise was that the channels on Mars identified as formed by seepage would be excellent sites to explore for signs of life because of the combined effects of sustained water (to cause erosion) and the subsurface nature of the flow (away from harmful UV radiation). However, fieldwork, literature review, and examination of images of Mars question the importance of seepage erosion on Mars. Similarly, the interpretation of waterfalls and channels in Kohala, Hawaii, and Box Canyon, Idaho has questioned the widely accepted inference that they formed by groundwater seepage. Field observations strongly suggest that the erosion of the canyon occurred by huge floods rather than seepage. The timing of these floods is constrained by He-3 exposure ages that indicate Box Canyon was formed between 100,000 and 50,000 years ago (this is the first demonstration of the combined U-Th-⁴He-³He approach to simultaneously dating the eruption age and exposure age of lava flows). Initial experimental and theoretical work suggests that block toppling may play a primary role in creation of amphitheater headwall during floods.

The idea that standing bodies of water might once have existed on Mars’ surface is supported by geologic and topographic features near the margins of the northern lowlands that have been interpreted as shorelines formed by ancient oceans. However, topographic profiles along the shorelines do not follow surfaces of equal gravitational potential, as the margins of a standing body of water should. We are testing the hypothesis that these long-wavelength topographic trends are the result of large-scale deformation of Mars’ surface. Our analysis indicates that the deformation mechanism might have been true polar wander, a change in the orientation of Mars’ rotation axis in response to a large redistribution of mass. Results suggest that this event could have been driven by the redistribution of water associated with the formation of the oceans. These findings support the idea that there were once extensive bodies of water on Mars that persisted over a geologically significant time interval.

The focus of our atmospheric and climate studies has been to investigate in the laboratory how easily a photochemical haze could have formed in the early atmospheres of Earth and Mars. Our results demonstrate that aerosol particles of high molecular weight organic molecules form more easily — that is, at lower CH₄-to-CO₂ ratios — than photochemical models have predicted, suggesting that hazes may have been prevalent on early Mars, which, in turn, may have had a dramatic effect on climate and habitability due to their effect on radiative transfer. Importantly for biosignature studies, preliminary measurements of the carbon isotopic composition of the particles formed in the laboratory showed no depletion in the ¹³C/¹²C ratio relative to the initial CH₄, suggesting that atmospheric photochemistry producing aerosol (and the settling of these organic particles to the surface) should not have contributed an abiotic “light” carbon signature to organic materials found in the martian rock record.

Geomicrobiological work was initiated at Box Canyon and other sites in order to evaluate the potential of water-rock interactions for sustaining chemoautotrophic microbial communities, especially those associated with iron cycling. Culture-based studies in the Fe seep material and weathered basalt have revealed significant numbers of both Fe(III)-reducing and Fe(II)-oxidizing microorganisms, indicating the potential for microbially-catalyzed Fe redox cycling. There is also evidence for the role of lithotrophic ammonium- and Fe(II)-oxidizers in the Fe seep community. In combination, the results indicate Fe(III)-reducing and Fe(II)-oxidizing bacteria contribute to tight coupled microbial Fe oxidation and reduction in the seep materials.

A variety of strains of neutrophilic iron-oxidizing bacteria have been physiologically characterized. Field-based studies have shown that iron-oxidizing bacteria are widespread. This result is potentially important, given that iron oxidation is an interesting candidate for an energy-generating system for life in the subsurface and on Mars. A new organism that forms a mineralized sheath has been discovered and described. The sheath is shed during growth. These, and other biomineralized structures formed by iron-oxidizing bacteria described previously by our group, may hold special potential as robust biosignatures. Funding has been secured for genomic characterization of six fresh-water iron-oxidizing bacteria so as to obtain clues to the genetic foundation of processes such as iron oxidation and sheath formation.

In other studies of microbial communities involved in iron cycling, we have developed methods that, for the first time, accurately measure in situ rates of iron oxidation microbial Fe mat communities. The oxidation rates correlate well with total iron content and appear to be influenced by the make-up or microbes in the community. Rates of oxidation on the same order of magnitude for cellular processes and autocatalysis suggest that bacteria harnessing Fe²⁺ as an energy source compete with their own byproducts for growth, and not strictly chemical oxidation. In contrast, studies at other sites indicate that iron oxidation is primarily attributable to cyanobacterial oxygen production.

We have also investigated coupled iron and sulfur cycling. Results show that FeSaq clusters are excellent catalysts mediating sulfide oxidation by molecular oxygen. Sulfide oxidation produces polysulfides, elemental sulfur and thiosulfate, which can be used by organisms to fix carbon via chemosynthesis. A variety of microorganisms participate in iron and sulfur cycling at low pH. Best known are the organisms responsible for iron oxidation, as this metabolism drives sulfide oxidation, release of dissolved iron, and acid formation. Recently we have identified novel, uncultivated archaea as contributors to sulfur oxidation at very low pH. Using cultivation-independent community genomic methods, we have also discovered a cluster of new archaeal lineages with no cultivated members. Results indicate that the cells are extremely small, smaller than any currently known cellular life form. It is unclear whether these organisms are free-living or parasitic on other organisms, but results appear to indicate a size smaller than that currently accepted to be the minimum for cells. Clues to the metabolism will be sought via genomic analysis of a filtrate using sequencing awarded for the purpose.

Isotopic analyses of Ca in a soil section from the Atacama desert, another Mars analogue site, reveal considerable and unexpected Ca isotope fractionation, which we believe is due to kinetic effects in the dissolution and reprecipitation of calcium carbonate and sulfate in the soil over millions of years. In addition, measurements and modeling of a deep-sea carbonate core and the associated pore fluids to evaluate the equilibrium fractionation factor for ⁴⁴Ca/⁴⁰Ca between calcite and aqueous solution show that slow inorganic precipitation of calcite results in no fractionation of Ca isotopes. This work provides the foundation for isotopic analysis of Martian meteorites.

We are currently investigating a sulfur spring system in a zone of high deformation in the central coast range of California where sustained groundwater discharge sites host extant microbial communities. We have evaluated the microbial community structure using a variety of cultivation-independent methods to provide insight into ecology of past terrestrial habitats of Earth and possibly Mars. These springs also provide access to significant carbonate accretions in which we have found some evidence for preservation of organic signatures. Analysis of the spectral properties of minerals has also been used to constrain the associated Mars environments.

Recently, we established a new focus study site at the hypersaline Lake Tyrrell, Australia. This previously identified Mars analog site has an active carbon cycling that is closely coupled to the iron and sulfur cycles. Initial cultivation-dependent studies of microorganisms and cultivation-independent analyses indicate relatively low diversity communities that will be suitable for comprehensive study by community genomic analysis (extensive high throughput sequencing to be supported by an NSF sequencing award). We have begun to analyze the lipid biosignature record in the lake sediments and correlate the historic lipid and pigment molecules with those in the contemporary microbial consortia. Information about the environment, lipid diagenesis, and microbial community structure may be directly applicable to analysis of ancient archaean hypersaline putative microbial communities.

Given that exploration of Mars may be largely achieved robotically, we are developing methods for robot-based geomicrobiology. 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 traversal of larger obstacles. Experimentation with the robotic manipulability of sand were done culminating in a demonstration of the robot digging with 2 modalities suitable to different grain size and water density. Comparisons with Martian photographs of wheel interactions with soil indicate applicable similarities. We have also devised a small robot to traverse over high viscosity liquids (waste deep mud), as is encountered at the Lake Tyrrell site. This is believed to be the first instance in the world of a robot this size scale to handle terrain of this nature.

The BioMARS team has an extensive education and outreach effort. We have developed BioMARS – Learning Interventions in Science Teaching materials that include step-by-step instructions for presenting hands-on, inquiry-based BioMARS activities to students, related background information, and a description of learning objectives. We are developing a multimedia piece that highlights iron-processing bacteria as a model for possible life on Mars that illustrates how important investigation design and detection systems are to BioMARS research. It uses time-lapse videography to show how iron-processing bacteria grow and develop and will include an interactive feature that allows students to make predictions, engage in discussions regarding predicted outcomes, and test these predictions. It will feature recently recorded discussions with several women and other scientists who are actively engaged in this type of research. Some of these materials and this approach will be incorporated into the newly developed GENE EPO project, based at the Lake Tyrrell research site. The GENE project has, as its primary objective, public participation in science with emphasis on original scientific discovery. To achieve this goal, materials are being developed (in collaboration with the Australian Astrobiology Institute) that make use of environmental genomic data as well as state of the art NASA-developed videography and other high tech learning tools.

Figure 1. Reconstuction illustrating the ocean that would have filed the (present) northern lowlands of Mars and the rotation pole at the time the oceans existed.

Figure 2. Images from a colonization slide taken from a freshwater iron mat showing a novel sheath-forming putative Fe-oxidizing bacterium. Two sheaths are shown. A. Phase contract image; B, the same image stained with Syto 13, a DNA binding dye and shown as a composite, one cell, stained green, is present in each sheath. A third cell is present attached to the exterior of S-shaped sheath. The cells are approximately 0.25 µm in diameter.