2000 Annual Science Report
NASA Jet Propulsion Laboratory Reporting | JUL 1999 – JUN 2000
Organic Molecules as Biosignatures
We currently have several research projects in progress that are related to the issue of identifying and evaluating biosignatures. We have collected a set of data on the fatty acid composition of Mono Lake water and sediments, which indicates that the level of early diagenesis in the lake is relatively low, and thus that preservation of organic biomarkers should be enhanced. We are following up these data with analysis of fatty acid carbon isotope signatures, in collaboration with Drs. Marilyn Fogel and James Scott of the Carnegie Institution of Washington.
We are also studying the temperature and environmental history of Siberian permafrost as revealed by the rate of amino acid racemization in permafrost core samples provided by Dr. David Gilichinsky of Russia. This study will allow us to evaluate more thoroughly claims that viable bacteria isolated from permafrost several million years in age have remained dormant without significant warming for their entire residence in the sediment. Data obtained so far indicate that the temperature of the permafrost below approximately 10 m has been relatively constant over time.
Another project currently underway involves the transport of organic material produced by cryptoendolithic organisms colonizing Antarctic rocks into the interior of those rocks. Soluble organics, including amino acids, appear to be transported into the abiotic interior of the rock by small flows of condensed atmospheric water. The amino acids detected in the rock interior so far show significant amounts of racemization, indicating that they have been in the interior for long periods of time and that the interior is free of living organisms. This environment represents perhaps the only place on Earth where potential organic biomarkers remain in contact with mineral matrices for extended periods of time without alteration by active biology.
We also continue with the determination of rate constants for oxidation of organic macromolecules by possible Martian oxidants. We have collected a data set consisting of rate constants for the oxidation of humic acid by dry hydrogen peroxide as a function of temperature. We are now incorporating these data with Martian annual maximum and minimum temperature data furnished by Prof. Bruce Jakosky of the University of Colorado.
We are continuing with a project involving the application of multivariate statistical techniques to the analysis of organic biomarker data from extraterrestrial samples. This work is currently focused on developing neural net algorithms that can distinguish between biological and non-biological amino acid profiles in meteorite or sediment samples.
Finally, we have in the past two years continued analyses of the amino acid content of Martian meteorites, most recently that of the meteorite Nakhla. The amino acid profile of this meteorite appears to be primarily terrestrial in origin, consistent with those of EETA79001 and ALH84001 previously analyzed.
PROJECT MEMBERS:Marilyn Fogel
RELATED OBJECTIVES:Objective 1.0
Determine whether the atmosphere of the early Earth, hydrothermal systems or exogenous matter were significant sources of organic matter.
Identify the environmental limits for life by examining biological adaptations to extremes in environmental conditions.
Search for evidence of ancient climates, extinct life and potential habitats for extant life on Mars.