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Amino Acid Biosignatures - Implications for the Detection of Extinct or Extant Microbial Communities on Mars

  • Author(s): Aubrey, Andrew D
  • et al.
Abstract

Investigations of Mars have recently found strong geochemical evidence for the presence of standing bodies of water early in the planet’s history. It still remains to be discovered whether organic compounds exist on Mars, a question which concurrent international scientific efforts are focused on for future in situ planetary missions. Amino acids are at the core of terrestrial biochemistry, ubiquitous in terrestrial life, and are easily detectable via highly advanced instrumentation with parts-per-trillion sensitivity making them an ideal biomolecular class to target during planetary exploration. Furthermore, amino acid chirality allows for the discrimination between compounds produced abiotically and those formed by biological processes, and these measurements can provide unequivocal evidence of extinct or extant life. The studies herein investigate organic components within Mars analog environmental samples and specifically characterize the concentrations and distributions of amino acids and their diagenetic products. Kinetic modeling of degradation reactions within ancient Mars analog minerals allows for the lifetimes of these bioorganic compounds to be estimated. The degree of amino acid preservation from an extinct biota will be much greater within Mars’ near-surface environments due to the characteristic cold temperatures and dry climates. Extrapolations of terrestrial amino acid stability models show the potential for preservation within sulfate minerals over billions of years on Mars.

High degrees of microscale variability, with respect to amino acid concentrations and distributions, are observed within the surface and immediate subsurface of Atacama Desert Soils and Antarctic rock samples which result from exposure to harsh surface conditions. All of these studies support the necessity of subsurface sampling procedures during future in situ robotic missions to Mars in order to detect and characterize well-preserved organic matter. Sulfate minerals appear to be prime targets for the search for evidence of extinct or extant life on Mars because of their high degrees of organic inclusion and observed persistence of amino acids within these minerals. The integration of advanced flight instrumentation such as the Urey instrument in future in situ mission payloads will offer the best chance of success in detecting biomolecular evidence of extinct or extant life on Mars.

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