QUANTIFYING THE ORGANICS LOAD WITHIN MANGANESE OXIDES USING MARS SPACEFLIGHT PYROLYSIS GC-MS TECHNIQUES

On Earth, Mn-oxidizing microorganisms (microbes) facilitate the formation of Mn oxides, which will only precipitate in high pH and Eh conditions. This intrinsic connection with microbes makes manganese deposits a potential biosignature, both on Earth and Mars. High concentrations of localized manganese oxides discovered on Mars suggest that strongly oxidizing conditions were present within select aqueous environments in the past. However, the biogenicity of these deposits as identified with rover payload instruments has not been assessed. While it is possible to determine the biogenicity of Mn-oxides on Earth using multiple lines of evidence and a suite of analyses, martian rover instrumentation is greatly limited. As one of the goals of future rover missions is to identify samples containing potential biosignatures, it is important to identify the biosignatures, if present, that would be detectable with the rover payloads.

The organics load from Mn-oxidizing microbial communities will be assessed in natural rock and water samples from New Mexico with pyrolysis gas chromatography-mass spectrometry (py-GC-MS). These approaches approximate the capabilities of select instruments on current and future Mars rover payloads and improve the ability to detect biosignatures in Mn-oxides, if present, on Mars. The GC-MS data indicate that alkanes are either not well preserved within Mn-oxides, or that the pyrolysis step impedes detection. Very few alkanes could be identified in any of the samples and the peaks that were present had extremely low abundance (<0.001 ng alkane/mg sample). More fatty acid methyl esters (FAMEs) were present than alkanes, but still at low abundance (<30 ng FAME/mg sample). Future work includes Bligh-Dyer extraction of organics to remove the pyrolysis step. Long-chain FAMEs (>C₂₀) were also present in the samples, which are usually indicative of higher order plants. This suggests that non-native organics are present on the samples. To determine if surface organics are present, samples were solvent washed and GC-MS analysis is on-going. Total organic carbon measurements of the samples are on-going to determine the organic load in the samples. By developing a thorough understanding of Mn biosignatures in the laboratory, we can remove significant ambiguities that exist in data collected on Mars.