| In this work, results are reported of Mossbauer analysis focused on a suite of samples collected systematically along the outflow channel from an iron-rich hydrothermal vent mound in the Chocolate Pots area of Yellowstone National Park in the context of Mars exploration. Similar hydrothermal spring systems may well have been present on an early Mars and could have harbored primitive life. Mossbauer spectroscopy was chosen as the primary investigative technique in this study because of its ability to discriminate among the iron-bearing minerals in these samples. Those on the surface and near the vent are identified as predominantly ferrihydrite, Fe5HO8 ˙ 4H2O or 5Fe2O3 ˙ 9H2O. Subsurface samples, which seem to have been altered by either inorganic and/or biological processes, exhibit spectral signatures that include nontronite Ca,Na 0.66Fe3+S4i7.34 Al0.66O20OH 4,nH2O, in the smectite clay mineral group, hematite (alpha-Fe 3+2O3), small-particle/nanophase goethite (alpha-Fe 3+OOH), and siderite Fe2+CO3 . Evidence is presented that all these minerals, including those with the nanophase property, can have multi-billion year residence times and thus survive from their possible production in a putative early Martian hydrothermal environment to present day. Mossbauer spectroscopy will be a planned component of the instrument suite included on the 2001 Mars Surveyor Athena Rover mission. It is hoped that this work will aid in the use of this instrument, in the service of exobiology, and in helping to identify hydrothermal sediments and samples suitable for subsequent return to Earth. |
