In-situ Mössbauer spectroscopy on Earth, Mars, and beyond Christian Schröder 1 , Göstar Klingelhöfer 1 , Richard V. Morris 2 , Bodo Bernhardt 3 , Mathias Blumers 1 , Iris Fleischer 1 , Daniel S. Rodionov 1,4 , & Jordi Gironés López 1 1 Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität, Staudinger Weg 9, D- 55099 Mainz, Germany (e-mail: schroedc@uni-mainz.de) 2 Astromaterials Research and Exploration Science, NASA Johnson Space Center, Mail Code KR, 2101 NASA Parkway, Houston, TX 77058, USA 3 Von Hoerner & Sulger GmbH, Schlossplatz 8, D-68723 Schwetzingen, Germany 4 Space Research Center IKI, Moscow, Russia ABSTRACT: Iron occurs naturally as Fe 2+ , Fe 3+ , and, to a lesser extent, as Fe 0 . Many fundamental (bio)geochemical processes are based on redox cycling between these oxidation states. Mössbauer spectroscopy provides quantitative information about the distribution of Fe among its oxidation states, identification of Fe-bearing phases, and relative distribution of Fe among those phases. Determination of Fe 3+ /Fe Total and the identification of iron hydroxide mineral phases, for example, provide evidence for aqueous activity on the surface of Mars. Metallic iron identified in several rocks investigated on Mars suggests a meteoritic origin. These Mössbauer spectra were obtained with portable, miniaturized spectrometers on board the NASA Mars Exploration Rovers. Because of their backscattering measurement geometry, the instruments are directly placed on the sample surface to be analyzed by a robotic arm. In field studies on Earth, similar instruments have been used for the in situ study of green rust in soil, and as a prospecting tool and process monitor during field testing of precursor hardware for lunar in situ resource utilization (oxygen production). An advanced version of the Mars spectrometer has a new detector system permitting shorter measurement times and the capability for simultaneous acquisition of X-ray fluorescence spectra to determine elemental compositions. KEYWORDS: Mössbauer spectroscopy, MIMOS IIa, Mars Exploration Rover, In-situ resource utilization, X-ray fluorescence spectroscopy INTRODUCTION Iron is one of the most abundant elements in the universe. Mössbauer (MB) spectroscopy is an established laboratory technique and a powerful tool to study Fe- bearing substances. The surface of Mars is Fe-rich compared to Earth, and a miniaturized MB spectrometer (MIMOS II) was developed for its robotic exploration as part of NASA’s Mars Exploration Rover (MER) mission (Klingelhöfer et al. 2003). The capability of simultaneous acquisition of X-ray Fluorescence (XRF) spectra has been added. This new instrument, capable of both mineralogical and chemical applications (Klingelhöfer et al. 2008) is briefly described and then a few examples of extraterrestrial and terrestrial applications are presented. MIMOS IIa INSTRUMENT DESCRIPTION Mössbauer Spectroscopy Available textbooks and reviews provide a detailed introduction to MB spectroscopy (e.g., Hawthorne 1988; Burns 1993). MB spectra provide quantitative information about the distribution of Fe among its oxidation and coordination states (e.g., octahedrally coordinated Fe 3+ ), identification of Fe-bearing phases, relative distribution of Fe among those phases, and can help to constrain crystallinity and particle size. MIMOS IIa MIMOS IIa is an advanced version of the MER instruments (Klingelhöfer et al. 2003) operating continuously since landing in January 2004. A new detector system has 1