A Moessbauer 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 Moessbauer spectrometer. In the context of future Mars exploration we present results of Moessbauer 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 Moessbauer 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 Moessbauer spectroscopy is at least as efficient in identification as X-ray diffraction. As a planetary surface instrument, Moessbauer spectroscopy can yield high-quality spectral data without sample preparation (backscatter mode). We have also used field emission scanning electron microscopy, in conjunction with energy-dispersive X-ray fluorescence spectroscopy, to characterize the microbiological component of surface sinters and the relation between the microbiological and the mineralogical framework. (Author)