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Definition and Detection of Biosignatures

The scientific focus of the Jet Proplusion Laboratory (JPL) Team is definition and detection of biosignatures that might be used to find evidence for extant or past life on Earth, in extraterrestrial environments, or within samples returned from extraterrestrial sites.

RESEARCH AREAS of the JPL TEAM

• Stable Isotopes of Biosignatures
  • nitrogen isotopes
  • carbon and sulfur isotopes
  • iron isotopes
  • transition metal isotopes

Research here focuses on microbiology, geomicrobiology, and interactions between microbes and metals of different types. These areas include work with stable isotopes, especially with stable iron isotopes, as well as with sulfur, carbon, and nitrogen isotopes.

• Reflectance Spectroscopic Biosignatures
  • large scale signatures in water bodies
  • reflectance signatures in soils and rocks

A part of our biosignatures research uses amino acid ratios as indicators of life. Work highlights here include two new and potentially very useful facts. First, amino acids (and their racemic signatures) are preserved for millions of years inside of Antarctic rocks where there are populations of endolithic bacteria near the surface. This allows one not only to estimate the amount of time that the rock has been populated, but would allow one (in principle) to identify a rock that had been (but was no longer) populated by endolithic bacteria. Second, using amino acid racemization analyses, it has been possible to estimate the temperature history of some Arctic permafrost samples, something very difficult to accomplish in the past.

• Life Detection Methodology – Biosignature Definition and Measurement
  • definition of non-earthcentric biosignatures
  • UV fluorescence and Raman methods
  • X-ray CT (computerized tomography) scanning methods
  • software development for life detection decision making and complexity analysis
  • study of extreme environments as analogues for extraterrestrial sites

The project on life detection methodology at JPL uses two new technologies for detection of potential life-containing strata. These two approaches are: deep UV (224 nm) fluorescence and CT X-ray scanning.

• Metal Oxide/Organism Interactions as Biosignatures
  • magnetite as a biosignature
  • iron oxidizing bacteria, and low pH metal alteration
  • iron and manganese oxidizing and reducing bacteria

Of particular note is our work providing a stand on the issue of magnetite as a biosignature, which defends the idea that magnetite in the ALH84001 meteorite is an indicator of past life on Mars. This is admittedly a controversial stance within the NAI group.