Lipid Biosignature Detection by TMSH Thermochemolysis and Pyrolysis GC-MS in the Mars-Analog Sediments of Hyperarid Qaidam Basin, China

Abstract:

Local environments that exhibit one or more characteristics of other worlds provide us with materials to test life detection techniques. In this study, the focus is Qaidam Basin, China, an analog for Gale Crater, Mars. Qaidam Basin exhibits several Mars-like traits, such as considerable hyperaridity, low annual temperature, high evaporation rates, many similar wind-driven geomorphological features such as yardangs, playas, and Barchan dunes, and fluvio-lacustrine features such as gullies and alluvial fans. Due to the hyperaridity of Qaidam Basin, complex molecules such as lipids that comprise cell membranes would have high preservation potential. To determine the lipid biosignature composition and extent of preservation in silty clay rock samples from Qaidam Basin, alkanes were determined with flash pyrolysis gas chromatography-mass spectrometry (GC-MS) experiments and trimethylsulfonium hydroxide (TMSH) thermochemolysis GC-MS was used to methylate and liberate fatty acids. Various aliphatic hydrocarbon chains were produced by flash pyrolysis, often favoring clear alkene fragmentation patterns over alkanes, however without a clear odd-over-even aliphatic chain number preference expected from a modern microbial community. With the addition of TMSH, various fatty acid methyl esters were produced with an even-over-odd chain length preference, indicating the preservation of microbial life. Thus, this method of analyzing organics preservation potential is fruitful for Mars analog samples in detecting and identifying these complex molecules. These techniques can be applied to in-situ analysis done by the Sample Analysis at Mars (SAM) instrument suite aboard the NASA Curiosity rover and in future rover payloads to detect evidence of past life on Mars.