ORGANICS DETECTION IN ACID MINE DRAINAGE SEDIMENTS, WITH IMPLICATIONS FOR ORGANICS PRESERVATION IN IRON RICH ACID AND SALINE ENVIRONMENTS ON MARS

Discovering whether past or present life exists on Mars is one of the most gripping questions of modern astrobiology. The distance between Mars and Earth results in the need for specialized instruments and techniques on Mars missions. One such technique utilizes pyrolysis gas chromatography mass spectrometry (GC-MS) to detect organic molecules preserved within the rock record. Both the NASA Curiosity and ESA ExoMars rovers can perform these experiments using their onboard GC-MS instruments, SAM and MOMA, respectively. These experiments can be simulated on Earth using acid-saline Mars analog samples acquired from schwertmannite, ferrihydrite, and goethite-bearing acid mine drainage (AMD) stream flocculent. By exploring the preservation of organic matter from extremophiles in AMD, the degree of organic preservation possible for select acid-saline environments on Mars can be extrapolated. The terrestrial site chosen for this was the Centralia AMD site in Pennsylvania which serves as an effective analog for the Burns formation on Mars. The primary target of these experiments are alkanes and fatty acids since they are ubiquitous components of microbial cells. Analyses performed with TMAH (tetramethylammonium hydroxide) 600°C flash pyrolysis were able to detect FAMEs from C₈ to C₂₀. These FAMEs displayed a clear even-over-odd preference which is indicative of modern microbial communities, though the C₂₀ FAME likely originated from higher order plant material found within the sample site. Similar trends were also detected in the net alkaline Packer-5 samples. Samples also underwent flash (600°C) pyrolysis and ramped (35°C/min) pyrolysis to detect the presence of alkanes. Flash pyrolysis analyses did not yield any identifiable alkanes; however, preliminary analysis of ramped pyrolysis data revealed alkanes ranging from C₈-C₁₇ in the Packer-5 samples. Further experiments will subject samples to a solvent wash prior to pyrolysis in order to strip the samples of any modern microbial communities. This will ascertain the extent to which FAMEs and alkanes are preserved within the AMD samples rather than on the surface. Overall, current analysis has shown GCMS pyrolysis to be an effective method of detecting microbial communities in AMD sites on Earth and as such would likely be effective in analogous sites on Mars.