2003 Annual Science Report
NASA Johnson Space Center Reporting | JUL 2002 – JUN 2003
Terrestrial Analogs and Martian Meteorites
Terrestrial analogs provide testing environments to better understand processes of life that may occur on other worlds, such as Mars. The Johnson Space Center (JSC) is dedicated to studying the mineralogy associated with microorganisms in Mars analog environments. One current mineralization study under Dr. Henry Chafetz is Mn- and Fe-rich hot spring deposits, which provided strong evidence that these were bacterially induced precipitates (Chafetz et al., 1998). Our desire is to now conduct a study of an active Mn- and Fe-precipitating system in order to acquire a better understanding of the conditions under which these types of deposits originate, that is, the physical, chemical, and biotic attributes of the system, and to establish criteria by which biotically induced Mn- and Fe-rich deposits can be recognized in the rock record. More research to note is by Dr. Kieft on microbial processes, which are: (1) characterization of dwarf microorganisms in an extreme environment, specifically desert surface soil; and (2) culture-dependent and culture-independent characterization of microorganisms in deep, hot subsurface environments, accessed via ultra deep gold mines in South Africa. Sampling in the gold mines has been primarily of flowing fracture waters. The water samples were filter to concentrate cells from which deoxyribonucleic acid (DNA) can then be extracted for characterization by 16S ribosomal DNA (rDNA)-based approaches. Our efforts have thus far yielded a multitude of novel sequences and cultures. Many of the cultures are thermophiles growing at 55-60°C. These include novel strains related to the bacterial genera Coprothermobacter, Geobacillus, Clostridium, Anaerobaculum, and also a previously uncultivated spirochete. Other mineralogical studies focus on hypersaline environments that would preserve biotic material through fossilization. Sites of this study include hypersaline tolerant biota from Storr’s Lake, San Salvador Island (Bahamas), Mono Lake (California), and the Dead Sea (Israel); they represent marine and nonmarine sites for comparative studies of potential analogs for interpreting some Mars meteorites and Mars sample return.
Defining locations where conditions may have been favorable for life is a key objective for the exploration of Mars. Of prime importance are sites where conditions may have been favorable for the preservation of evidence of pre-biotic or biotic processes. Areas displaying significant concentrations of the mineral hematite (α -Fe2O3) have been identified from orbit by thermal emission spectrometry. Therefore we are investigating morphology and mineralogy associated with terrestrial life found in rock varnish, banded iron formations and ferricrete. We have also begun collaboration support with the U.S. Geological Service (USGS) and the University of Arizona to investigate microbial ecology and preservation mechanisms in the Atacama Desert. The Atacama Desert in Northern Chile is the coldest, driest and highest desert on Earth. The high altitude and dry conditions the Atacama make it the best terrestrial analog for Mars studies. The primary force controlling mineralization in these systems are the microbes because of their ability to attract both actively and passively metallic ions on their surfaces, and to alter the chemistry of the immediate environment through secretion of biofilms.
The best Mars analog is an actual piece of Mars. JSC continues to study Martian meteorites, looking at terrestrial contaminants as well as indigenous organics and mineral biosignatures. The range of these studies is reported in the Organics Biosignatures and Mineral Biosignatures project reports. Other mineralogical studies of Martian Meteorites include carbonate and weathering products preserved in the Martian Meteorites. These results yield that ALH84001, Nakhla and Shergotty all contain indigenous evaporates from subsurface water circulating through fractures in the rock. Martian meteorite EETA79001 has also preserved remnants of the Martian regolith. The regolith contains part of the weathering record of Mars. Dr. Rao continues his studies to better understand the late weathering nature of this shergottite and what it implies to the weathering history of Mars.
PROJECT INVESTIGATORS:David McKay
PROJECT MEMBERS:Carlton Allen
RELATED OBJECTIVES:Objective 2.1
Outer Solar System exploration
Environmental changes and the cycling of elements by the biota, communities, and ecosystems
Biosignatures to be sought in Solar System materials