Organic Matter Detection on Mars by Pyrolysis-FTIR: An Analysis of Sensitivity and Mineral Matrix Effects

Abstract

Returning samples from Mars will require an effective method to assess and select the highest-priority geological materials. The ideal instrument for sample triage would be simple in operation, limited in its demand for resources, and rich in produced diagnostic information. Pyrolysis–Fourier infrared spectroscopy (pyrolysis-FTIR) is a potentially attractive triage instrument that considers both the past habitability of the sample depositional environment and the presence of organic matter that may reflect actual habitation. An important consideration for triage protocols is the sensitivity of the instrumental method. Experimental data indicate pyrolysis-FTIR sensitivities for organic matter at the tens of parts per million level. The mineral matrix in which the organic matter is hosted also has an influence on organic detection. To provide an insight into matrix effects, we mixed well-characterized organic matter with a variety of dry minerals, to represent the various inorganic matrices of Mars samples, prior to analysis. During pyrolysis-FTIR, serpentinites analogous to those on Mars indicative of the Phyllocian Era led to no negative effects on organic matter detection; sulfates analogous to those of the Theiikian Era led, in some instances, to the combustion of organic matter; and palagonites, which may represent samples from the Siderikian Era, led, in some instances, to the chlorination of organic matter. Any negative consequences brought about by these mineral effects can be mitigated by the correct choice of thermal extraction temperature. Our results offer an improved understanding of how pyrolysis-FTIR can perform during sample triage on Mars. Key Words: Mars—Life-detection instruments—Search for Mars’ organics—Biosignatures. Astrobiology 16, 831–845.

Infrared Spectroscopic Detection of Biosignatures at Lake Tírez, Spain: Implications for Mars

“…When sulfates decompose, they release oxygen on heating which may oxidize organic matter present in the sample of interest. A benefit of searching for biosignatures on Mars within gypsum and magnesium sulfates is that they are unlikely to yield oxygen at the temperatures commonly employed for the thermal extraction of organic matter, as under these conditions gypsum only dehydrates (West and Sutton, 1954;Gordon and Sephton, 2016). Due to the potential issues with organic detection and pyrolysis, however, it is important to be able to analyze and search for biosignatures by using nondestructive techniques, such as the IR spectroscopy utilized in this study.…”

Is Searching for Martian Life a Priority for the Mars Community?

“…The Mars community, including NASA and ESA, always points to life detection as a number-one priority in Mars exploration ( i.e., Grossman, 2013 ; McKay et al, 2013 ; Heldmann et al, 2014 ; King, 2015 ; Vago et al, 2015 ; Gordon and Sephton, 2016 ; Levin and Straat, 2016 ; Ehlmann et al, 2017 ; Hubbard, 2017 ; Niles et al, 2017 ; Smith et al, 2017 ; Xie et al, 2017 ; Hand, 2018 ; Michalski et al , 2018 ). This position is also well summarized in (i) the motivating goal #1.B of the Mars Exploration Program: “Determine if environments with high potential for current habitability and expression of biosignatures contain evidence of extant life” (MEPAG, 2015 ; italics added); (ii) the fact that the NASA Astrobiology Institute was established shortly after the possible detection of fossilized life on Mars (McKay et al, 1996 ); (iii) the initiative that the Chairs of the Mars Habitability Session at the 2010 Astrobiology Science Conference took to ask for adding a life-detection mission into the NASA Decadal Survey, which included a petition signed by more than 130 scientists, most of them still active in the Mars science community (Schulze-Makuch and Davila, 2010 ); and (iv) the debate held recently in this journal (the leading journal in the field) regarding the search for life on Mars (Schulze-Makuch et al, 2015 ).…”

A Method for Choosing the Best Samples for Mars Sample Return

“…Measurements of spectral features were taken and recorded: a peak located at 2349 cm −1 corresponding to the anti-symmetric stretch in carbon dioxide, one at 3853 cm −1 arising from a stretching mode of water, one at 1352 cm −1 corresponding to the sulfur dioxide anti-symmetric stretching mode, one at 3016 cm −1 corresponding to the methane anti-symmetric stretching mode and the height of a peak at 2933 cm −1 . Organic compounds, depending on the molecular composition and structure, typically produce features in a broad spectral window corresponding to the C-H stretch; for comparison with a previous study (Gordon and Sephton, 2016a ), the region (3150–2740 cm −1 ) was chosen to represent organic compounds. The mass of methane, water, carbon dioxide, and sulfur dioxide products were determined by reference to mass calibration curves.…”

“…To identify samples of highest priority for biosignature detection, a triage methodology was developed. A phased approach was adopted to utilize the advantages of different modes of pyrolysis-FTIR (the advantages of the chosen modes had been determined in previous investigations [Gordon and Sephton 2016a , 2016b ]). The phases were designed to occur in a sequence: an initial habitability assessment phase, a subsequent habitation assessment phase, and a final diagnostic phase.…”

“…Pyrolysis-FTIR has been demonstrated to provide diagnostic information on the mineralogy of samples and therefore past habitability (Gordon and Sephton, 2016b ). Pyrolysis-FTIR has also been utilized to provide insights into the probability of the presence of biosignatures, demonstrating that detection of organic compounds in concentrations as low as tens of parts per million is achievable (Gordon and Sephton 2016a ).…”