Targeting organic molecules in hydrothermal environments on Mars

Details Targeting organic molecules in hydrothermal environments on Mars Targeting organic molecules in hydrothermal environments on Mars

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..900p&link_type=abstract

European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a

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Hydrothermal deposits on Mars Hydrothermal systems are proposed as environments that could support organic synthesis, the evolution of life or the maintenance of life [1,2,3]. They have therefore been suggested as primary targets for exploration on Mars [1,2,4,].There is now confidence that hydrothermal deposits occur at the martian surface. This is based on a range of criteria that could point towards hydrothermal activity, including volcanic activity, magmatic-driven tectonism, impact cratering in icy terrains, hydrous alteration of minerals and typical hydrothermal mineralogies [4]. The proposals to search for evidence of life at martian hydrothermal sites have been focussed on seeking morphological evidence of microbial activity [5]. Here we discuss the potential to seek a chemical signature of organic matter in hydrothermal systems. Organics in terrestrial hydrothermal systems Terrestrial hydrothermal systems can have large quantities of organic matter because they intersect organic-rich sedimentary rocks or oil reservoirs. Thus the signatures that they contain reflect some preexisting concentration of fossil organic compounds, rather than life which was active in the hydrothermal system. If any extant life was incorporated in these hydrothermal systems, it is swamped by the fossil molecules. Examples of environments where organic materials may become entrained include subsurface hydrothermal mineral deposits, generation of hydrothermal systems by igneous intrusions, and hot fluid venting at the seafloor. Nevertheless, there is value in studying the interactions of hydrothermal systems with fossil organic matter, for information about the survivability of organic compounds, phase relationships between carbonaceous and noncarbonaceous materials, and where in hydrothermal deposits to find evidence of organic matter. Microbial colonization of hot spring systems is feasible at depth within the systems and at the surface where the hydrothermal waters discharge. Discharging fluids will also precipitate minerals due to drop in temperature and pressure, and colonising organisms are likely to become entrained by the minerals. Attempts to find evidence of microbial activity related to hydrothermal systems in the geological record have therefore been focussed on hydrothermal mineral precipitates. Organic matter is found in hydrothermal precipitates back into the Precambrian [6]. Fig. 1 Settings for organic matter in hydrothermal systems. Surface discharge could be in subaerial or subaqueous environment. Application of SERS Studies using conventional laser Raman instruments have made a good case for application of this type of spectroscopy to planetary exploration. The detection of pigments sited in microbial matter in a range of samples from extreme environments (e.g. [7]) has supported development of the technique for space exploration generally, and Mars exploration in particular [8]. A major advantage of conventional Raman spectroscopy is that it can be applied to simultaneous characterization of bond types in both organic and inorganic materials. Surface-Enhanced Raman Spectroscopy (SERS) increases the sensitivity by several orders of magnitude, and overcomes the problems created by natural fluorescence [9]. SERS is achieved by adsorbing the target analyte onto the surface of a metal. We are combining the additional sample processing necessary for SERS with sample preparation in a microfluidic format (including extraction and sample concentration). The final result will be a very rapid assay, capable of detecting ppb concentrations of certain organic analytes. This approach was tested at a site in Iceland, where young/active hydrothermal systems are focussed in a rift environment. Sulphur species are prevalent, in a range of oxidation states, including sulphates, sulphides and native sulphur. Thus they are a useful model for systems that might exist on Mars, where sulphur species are widespread and therefore likely to be incorporated into hydrothermal systems. Microbial colonization of the Iceland sites is evident as pigmentation, which is amenable to SERS. The pigments detected by SERS are particularly phycocyanin, scytonemin and β,β carotene (Fig. 2), the distribution of which is controlled by water temperature. A SERS response is obtained from sinters as well as active hydrothermal discharges. This successful application of SERS indicates a potential technique for the exploration for organic compounds in martian hydrothermal systems.

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