Manson L. Wade

A Mossbauer investigation of iron-rich terrestrial hydrothermal vent systems: Lessons for Mars exploration

Hydrothermal spring systems may well have been present on early Mars and could have served as a habitat for primitive life. The integrated instrument suite of the Athena Rover has, as a component on the robotic arm, a Mossbauer spectrometer. In the context of future Mars exploration we present results of Mossbauer analysis of a suite of samples from an iron-rich thermal spring in the Chocolate Pots area of Yellowstone National Park (YNP) and from Obsidian Pool (YNP) and Manitou Springs, Colorado. We have found that Mossbauer spectroscopy can discriminate among the iron-bearing minerals in our samples. Those near the vent and on the surface are identified as ferrihydrite, an amorphous ferric mineraloid. Subsurface samples, collected from cores, which are likely to have undergone inorganic and/or biologically mediated alteration (diagenesis), exhibit spectral signatures that include nontronite (a smectite clay), hematite (alpha-Fe2O3), small-particle/nanophase goethite (alpha-FeOOH), and siderite (FeCO3). We find for iron minerals that Mossbauer spectroscopy is at least as efficient in identification as X-ray diffraction. This observation is important from an exploration standpoint. As a planetary surface instrument, Mossbauer spectroscopy can yield high-quality spectral data without sample preparation (backscatter mode). We have also used field emission scanning electron microscopy (FESEM), in conjunction with energy-dispersive X ray (EDX) fluorescence spectroscopy, to characterize the microbiological component of surface sinters and the relation between the microbiological and the mineralogical framework. Evidence is presented that the minerals found in these deposits can have multi-billion-year residence times and thus may have survived their possible production in a putative early Martian hot spring up to the present day. Examples include the nanophase property and the Mossbauer signature for siderite, which has been identified in a 2.09-billion-year old hematite-rich chert stromatolite. Our research demonstrates that in situ Mossbauer spectroscopy can help determine whether hydrothermal mineral deposits exist on Mars, which is significant for exobiology because of the issue of whether that world ever had conditions conductive to the origin of life. As a useful tool for selection of samples suitable for transport to Earth, Mossbauer spectroscopy will not only serve geological interests but will also have potential for exopaleontology.

Mössbauer spectroscopy as a tool in the search for evidence of past life on Mars

Iron Mössbauer spectroscopy has provided evidence for the presence in deep-sea smoker vents of superparamagnetic material, which is correlated with anaerobic bacteria found to thrive there. The finding of superparamagnetic terrestrial vent material suggests that prospecting for such material on Mars may be a way to locate sites with micropaleontological potential.

Optimization of the glycine‐metal nitrate combustion method for preparing barium ferrite (abstract)

A combustion‐synthesis method1 has been adapted2 for the preparation of barium ferrite. In this method, stoichiometric amounts of metal‐nitrate solutions are mixed and glycine (aminoacetic acid) is added at specific glycine/metal‐nitrate ratios. The resulting solution is then heated until autoignition (combustion). The combustion products for several G/N ratios have been analyzed by XRD, Mossbauer spectroscopy, and EDS; they consist of hematite and/or maghemite with traces of residual barium nitrate that vary according to the G/N ratio. Packing experiments reveal a dramatic variation in density of the powdered combustion products ranging from 0.08 to 0.87 g/cm3 for G/N=0.4 to 0.7 molar, respectively. SEM micrographs show what appear to be sintered ceramic flakes of undetermined particle shape. Barium ferrite is obtained with subsequent heat treatment. Along with TEM, SSA, and VSM analysis of the combustion products and the converted barium ferrite, a DTA determination of minimum phase‐change temperature f...

Synthesis and Characterization of Pure Barium Ferrite Prepared by a Glycine - Metal Nitrate Combustion Method

A combustion-synthesis method [Chick et al ., Materials Letters 10, 6 (1990)] has been adapted for the efficient preparation of pure barium ferrite particles, BaFe 12 O1 9 . Solutions of Ba(NO 3 ) 2 and Fe(NO 3 ) 3 · 9H 2 O were mixed in stoichiometric amounts and glycine (aminoacetic acid) was then added according to the desired glycine / nitrate ratio. The solution was heated to around 200°C, when combustion occured, yielding a highly magnetic ash, which XRD suggests consists of extremely fine-grained γ-Fe 2 O 3 and Ba 3 Fe 2 O 6 . Subsequent heat-treatments of 1050°C for 1.5 hr or 1200°C for 1 hr converted the ash to pure barium ferrite, as determined by XRD and Mdssbauer spectroscopy. Single-crystal platelets of barium ferrite, identified by SEM, varied dramatically in size with heat-treatment (diameter ∼0.2 pm and 6 μm, respectively), as did coercivity, measured by VSM (∼5000 Oe and 2500 Oe, resp.), while magnetization was unaffected.