New Method for the Detection of Organosulfur Biosignatures in Mars-Analog Terrestrial Sedimentary Facies

Abstract:

Thiols are the dominant form of sulfur in terrestrial organisms where they are present in the amino acids cysteine and methionine as well as various co-enzymes. Despite their biogeochemical importance, thiols are not typically evaluated as biosignatures of past life because their high reactivity prevents analysis by GC-MS and suggests they would likely not be preserved over geological timescales. Employing microchip capillary electrophoresis coupled to fluorescence detection we observed thiols in samples from a ~200 million year old methane seep in the south of England. In order to identify the thiol in the sample we have developed a new GC-MS method that involves derivatization of thiols with a trialkysilyl reagent (MSTFA). We are currently optimizing the method to improve the yield of derivatization and to maximize chromatographic separation.

The abundance of sulfur on Mars has been confirmed by numerous data from both in situ and remote sensing instruments. Most recently, NASA's Curiosity Mars rover detected calcium sulfates and iron sulfides among the sedimentary rocks at Yellowknife Bay. In anticipation of a Mars sample return mission, we have begun collection and evaluation of Mars-analog sedimentary facies for the presence of thiols. Discovery of thiols in martian rocks would provide strong evidence for a biologically-mediated sulfur cycle on Mars.