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Project Progress

In anticipation of human exploration, analytical strategies are urgently needed to characterize organic molecules in chemical and clastic deposits inferred to be present on or near the surface of Mars. Although organic compounds associated with clay minerals are relatively well studied, surprisingly little is known about sequestration of simple organic molecules in fluid inclusions and interfacial water or as sorbed and solid materials in halides and sulfates. Detection of sulfate minerals on the Martian surface by Viking and verification by Mars Exploration Rovers and orbital spectroscopic instruments emphasizes the need to understand preservation and possible catalytic activity of biologically relevant molecules in chemical precipitates from Martian brines. Therefore, a series of experiments was initiated with the intension of characterizing the distribution of amino acids and peptides during diurnal sub-freezing evaporitic cycles under a low-pressure carbon dioxide atmosphere with radiation and temperature regimes that mimic Martian surface conditions. We are specifically interested in 1) rates of amino acid racemization and degradation 2) catalytic properties of evaporitic minerals for potential polymerization of amino acids; 3) crystal boundaries and fluid inclusions as sites for preservation of simple organic molecules; and 4) effects of ultra-violet radiation on hydration, dehydration, and solvation of amino acids in sulfate evaporites.

Micromolar concentrations of glycine, L-alanine, L-valine, L-aspartic acid, and L-glutamic acid, representative of some 107 cells/milliliter of sample are suspended in carbon-dioxide equilibrated, millimolar brine solutions. Assuming that the composition of a Martian paleo-lake would be derived from the weathering of olivine-bearing basalts by neutral to moderately acidic water flow, brines are composed of magnesium, calcium, sodium and sulfate, with acetate constituting the remaining charge balance. Ferrous iron is also included in solution to mimic a more acidic weathering environment and facilitate the formation of acidic mineral assemblages such as jarosite. Amino-acid amended brines were reacted for two weeks in a Mars simulation chamber at Space Hardware Optimization Technology Incorporated, located in Greenville, Indiana. The atmosphere in the simulation chamber was carbon dioxide at a pressure of 40-150 millibars, with pressures occasionally reaching over 500 millibars due to vacuum loss. Twelve-hour light and dark cycles with ultraviolet radiation at a maximum flux of 50 micromoles of photons per square meter in the 240-400 nanometer range were used to imitate Martian daylight. Temperature endpoints were about 25o centigrade inside the chamber during the light hours and -40o centigrade in the dark hours. Cyclic thawing and freezing of samples is observed through a small window in the chamber. After removal from the chamber, precipitated samples and remaining brines were stored at -20 centigrade prior to analysis of mineral phases using X-ray diffraction and amino acid degradation and racemization using gas chromatography with a chiral selective column.

Precipitated samples were analyzed for mineralogy using x-ray diffraction and were found to contain end member combinations of gypsum, hexahydrite, epsomite, and minor carbonate phases. However, due to incomplete precipitation of mineral phases during the experiment cycle as evidenced by the remaining presence of brine, the complete suite of mineral phases to form under a Martian diurnal cycle was unavailable. However, future experimental parameters will ensure the complete dessication of brines and various rehydration phases characteristic of the present day Mars surface. Current analysis continue examining how the presence of organic compounds in the experimental setup alter the diffraction pattern of this limited sample suite, and explore how the presence of ultraviolet radiation affects the types of end member mineral facies.
Amino acid analysis is currently underway on a dedicated Hewlett Packard 5890 Gas Chromatograph fitted with an automated splitless injection column. The instrument is equipped with a enantiomer selective column with a flame ionization detector. Precipitated mineral samples are acid vapor hydrolyzed for 24 hours at 110° centigrade to liberate bound amino acids from the sample. Hydrolysates are collected, desalted and derivatized to their n-pentafluoropropionyl-amino acid isopropyl esters prior to analysis. Previous months were used in repairing and dedicating the instrument to amino acid analysis and then the analysis of both pure and racemic samples of amino acids to verify the correct elution of amino acid stereoisomers and develop calibration plots for each species. Sample analysis is currently underway and should proceed much more rapidly with the development of an analytical procedure that will facilitate accurate and reproducible data.

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