NASA Astrobiology Institute (NAI)

1. Biosignatures in Extraterrestrial Samples

   Project Investigators:

   Other Project Members

   David McKay (Principal Investigator)

   Dennis Bazylinski (Co-Investigator)

   Mary Sue Bell (Research Staff)

   George Flynn (Co-Investigator)

   Everett Gibson (Co-Investigator)

   Chris Romanek (Co-Investigator)

   Craig Schwandt (Co-Investigator)

   Andrew Steele (Co-Investigator)

   Kathie Thomas-Keprta (Co-Investigator)

   Allan Treiman (Co-Investigator)

   Susan Wentworth (Co-Investigator)

   Astrobiology Roadmap Objectives:

   • Objective 8: Search for evidence of ancient climates, extinct life and potential habitats for extant life on Mars.
   • Objective 16: Understand the human-directed processes by which life can migrate from one world to another.

   Project Progress

   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.
   

Publications