2000 Annual Science Report
NASA Johnson Space Center Reporting | JUL 1999 – JUN 2000
Biosignatures in Extraterrestrial Samples
This project concentrates on studying the martian meteorites in our systematic search for biosignatures in extraterrestrial samples. The research by JSC and Co-Investigator scientists currently includes four major biological / organic investigations, analysis of magnetite crystals, analysis of features morphologically similar to fossilized terrestrial organisms, detection of trace-level organic compounds, and assessment of terrestrial microbial contamination.
In addition, we are conducting ongoing studies of chemical weathering on Mars and on Earth, and analyzing experimental shock effects to document the possibility of biomarker preservation in meteoritic materials. Finally, we have proposed to broaden the Astrobiology investigation of these unique extraterrestrial samples through a new Inter-Institute Focus Group on Martian Meteorites.
Several Project Reports (dm)
Analysis of magnetite crystals
Using transmission electron microscopy (TEM), we have analyzed magnetite crystals extracted from carbonate globules in the martian meteorite ALH84001. Of the ALH84001 magnetites that we have examined, one population called elongated prismatic (~27% of the total) are indistinguishable from magnetites produced by certain strains of terrestrial magnetotactic bacteria. In addition, there is no known inorganic population of magnetites that is analogous to the ALH84001 elongated prisms. Since we are confident that these magnetite crystals are not a terrestrial contaninant (see below), our interpretation is that the ALH84001 elongated prismatic magnetites were likely formed by biogenic processes on Mars.
Analysis of features morphologically similar to fossilized terrestrial organisms
Using high resolution scanning electron microscopy, we have continued our examination of martian features that are morphologically and chemically identical to known terrestrial mineralized or fossilized cells and/or cellular appendages. Our interpretation is that these features, present in the martian meteorites ALH84001, Nakhla, and Shergotty, may have been formed by biological processes on Mars.
Detection of trace-level organic compounds
We have used Time-of-Flight Secondary Ion Mass Spectrometry to analyze specific features in the two martian meteorites ALH84001 and Nakhla for the presence of trace-level organic compounds. We have observed spatial relationships among some purported martian fossilized cells and certain organic compounds. Future work on the organic analysis of known terrestrial biogenic features will help to determine if organic compounds found in the martian meteorites may be interpreted as biomarkers.
Assessment of terrestrial microbial contamination
We have used scanning electron microscopy (SEM) and DNA/PCR analyses to determine the extent of contamination in martian meteorites ALH84001 and Nakhla. It is clear that portions of all meteorites are contaminated with terrestrial materials (e.g., organic compounds, bacteria). If some of the fossilized biogenic-like forms in these meteorites are the mineralized remains of martian organisms, then we must differentiate between indigenous martian features and terrestrial contamination. This is possible only if we can constrain the extent and type of terrestrial contamination associated with each martian meteorite. Our work shows that there are terrestrial bacteria and fungi living within and on the surfaces of ALH84001 and Nakhla. Our interpretation is that these terrestrial organisms are morphologically distinguishable from those we interpret as purported fossilized martian cells or cellular appendages.
PROJECT MEMBERS:David McKay
Mary Sue Bell
RELATED OBJECTIVES:Objective 8.0
Search for evidence of ancient climates, extinct life and potential habitats for extant life on Mars.
Understand the human-directed processes by which life can migrate from one world to another.