E. Kankeleit

Jarosite and Hematite at Meridiani Planum from Opportunity's Mossbauer Spectrometer

Mössbauer spectra measured by the Opportunity rover revealed four mineralogical components in Meridiani Planum at Eagle crater: jarosite- and hematite-rich outcrop, hematite-rich soil, olivine-bearing basaltic soil, and a pyroxene-bearing basaltic rock (Bounce rock). Spherules, interpreted to be concretions, are hematite-rich and dispersed throughout the outcrop. Hematitic soils both within and outside Eagle crater are dominated by spherules and their fragments. Olivine-bearing basaltic soil is present throughout the region. Bounce rock is probably an impact erratic. Because jarosite is a hydroxide sulfate mineral, its presence at Meridiani Planum is mineralogical evidence for aqueous processes on Mars, probably under acid-sulfate conditions.

Mössbauer mineralogy of rock, soil, and dust at Meridiani Planum, Mars: Opportunity's journey across sulfate-rich outcrop, basaltic sand and dust, and hematite lag deposits

Additonal co-authors: P Gutlich, E Kankeleit, T McCoy, DW Mittlefehldt, F Renz, ME Schmidt, B Zubkov, SW Squyres, RE Arvidson

Mössbauer spectroscopy in space

Nearly 40 years after the discovery of the Mössbauer effect for the first time a Mössbauer spectrometer will leave our planet to explore in situ the surface of another solar system body: the red planet Mars [1]. We are currently developing a miniaturized Mössbauer spectrometer (MIMOS) which is part of the scientific payload of the Russian Mars96 mission, to be launched within the next 2–4 years [2,3]. To fulfill the requirements for a space mission to the planet Mars, all parts of the spectrometer had to be extremely miniaturized and ruggedized to withstand the space flight and Mars environmental conditions. The relevant parts (e.g. drive, detector system, electronics etc.) will be described in more detail and its characteristics compared to standard systems. Because of this new development there now is a growing interest to include a Mössbauer (MB) instrument in future space missions to other solar system bodies as for instance Venus, the terrestrial Moon, and a comet nucleus. Because of extremely different environmental conditions (e.g. nearly zero gravity on the surface of a comet nucleus, high pressure and temperature on the surface of Venus, etc.) different instrument designs and concepts are required for different missions. We will present some ideas for various types of missions, as well as the motivation for using Mössbauer spectroscopy in these cases.

The Miniaturized Mössbauer Spectrometer MIMOS II for Extraterrestrial and Outdoor Terrestrial Applications: A Status Report

In May and July 2003 both the European space agency ESA and the American space agency NASA will launch space missions to Mars. The ESA lander Beagle 2 and the two NASAMars-Exploration-Rovers (MER) will explore the Martian surface with a set of sophisticated instruments. Part of the payload will be our miniaturized Mossbauer spectrometer MIMOS II. It operates in backscattering geometry and meets the requirements for space application of low mass (⩽500 g), small volume (coke can size), and low power consumption (⩽3 W). Main goals are the determination of the oxidation state of iron and the iron mineralogy on the surface. This information will contribute to a much deeper understanding of the evolution of the planet Mars, its surface and atmosphere, and the history of water. The MIMOS II flight units for MER were delivered in April 2002 to the NASA Jet Propulsion Laboratories (JPL), California, for integration to the Rovers. After some more testing of the complete Rover system the spacecraft will be shipped to the Kennedy Space Center early February 2003. The first launch will be in May 2003 and the second launch in late June on early July 2003. The flight unit for the ESA Mars-Express Beagle lander was delivered to ESA by the end of May 2002 for integration to the lander in late November/early December 2002. The launch is scheduled for June 2003 from Baikonur, Kazakhstan. The instrument MIMOS II is also under consideration for an ESA space mission to Mercury in 2009, and it is part of the ESA exobiology multi-user facility to be launched as part of one of the next lander Mars missions after 2005.

Remarks on depth selective CEMS — Backscattering measurements

Depth Selective Conversion Electron Mössbauer (MB) Spectroscopy measurements usually are done in backscattering geometry under bad geometrical conditions due to low resonant count rates. Furthermore in the case of iron these investigations are often done on samples enriched with57Fe, partially polarized. Because of these conditions the spectra are modified more or less strongly by the cosine smearing effect and/or saturation effects due to high enrichment of57Fe. We have investigated these effects in the case of an α-Fe-metal sample using a high transmission orange spectrometer.

Mössbauer backscattering spectrometer for mineralogical analysis of the mars surface

A Mössbauer spectrometer for the mineralogical analysis of the Mars surface is under development. This instrument will be installed on a Mars-Rover, included in the Soviet Union Mars-94/96 Mars mission. Due to power and mass restrictions the electromechanical drive and the electronic components have been extremely miniaturized in comparison to standard systems. Solid state detectors (PIN-diodes) are used for γ- and x-ray detection. The whole spectrometer is controlled by a microprocessor (transputer). An additional application as x-ray fluorescence spectrometer is proposed.

IN-SITU PHASE ANALYSIS BY A VERSATILE MINIATURIZED MOSSBAUER SPECTROMETER

The element iron plays a major role in modern industries and technologies as for instance car-industry, mineral processing and steel production and power plants. For quality control, process monitoring and device inspection (e.g., pipes in power plants) a fast, non-destructive and sensitive analytical method is desirable. 57Fe Mössbauer spectroscopy is able to determine the different iron phases (e.g., oxides, sulfides, nitrates, carbonates and carbides) and therefore would be the ideal tool to perform this job. We have developed a miniaturized backscattering Mössbauer spectrometer for space applications which will be modified and used for industrial applications under certain circumstances. The instrument is designed in a modular way which would allow to adapt it to different applications. The instrument has approximately the size of a soft drink can, a weight of about 0.5 kg, and a power consumption of about 3 watts.

Surface sensitivity of low energy electron Mössbauer spectroscopy (LEEMS) using57Fe

Very low energy electrons (LEE) (Ee≤15 eV) are produced with high intensity directly by Mössbauerabsorption and conversion in the case of57Fe [1, 4, 5]. These electrons should be very surface sensitive due to their very low attenuation length compared to the 7.3 keV K-Conversion electrons of57Fe [5, 11]. We have examined the surface sensitivity of these resonant LEE, using nonresonant56Fe metal and56Fe stainless steel foils coated with about 20 Å and 50 Å57Fe, respectively. They were exposed to air after evaporation: The 20 Å samples are found to be fully oxidized [5]. Depth Selective Conversion Electron Mössbauer Spectroscopy (DCEMS), performed with a high transmission orange type magnetic spectrometer [5, 6, 13] reveals a two layer structure of the 50 Å samples. Low Energy Electron Mössbauer Spectroscopy (LEEMS) [5] is found to be significantly more surface sensitive than conventional DCEMS, but not as surface sensitive as Auger Electron Mössbauer Spectroscopy (AEMS) using LMM-Auger electrons of 500–600 eV, as expected due to the different mean free path. But because of the very low intensity of these Auger electrons this mode appears to be not very useful for practical application.

Iron ore processing -- in-situ monitoring

Mössbauer spectroscopy has been used to provide detailed quantitative insight into the reaction products present at different stages of the processing/reduction of iron ores. Typical phases include: α-Fe2O3; Fe3O4; Fe1-xO; Fe3C and Fe, which are in agreeement with the results obtained using standard wet chemistry methods. As an extension of this post reaction examination of products, we have used Mössbauer spectroscopy for in-situ measurements during the week long operation of an iron ore processing pilot plant. Such in-situ measurements allow optimal control of the plant to be obtained with, depending on the strength of the source, a time constant of ~ 1 h.

Critical behavior of the surface of FeBO3 single crystals

The behavior of the surface and near-surface layers of macroscopic FeBO3 single crystals is studied over the temperature range from 291 K to Neél temperature (TN) using depth-selective conversion-electron Mössbauer spectroscopy. Three different phases or states, namely, an antiferromagnetically ordered phase (similar to the crystal bulk state), a surface phase, and a transition layer between them coexist near the Neél point in a surface layer ∼500 nm thick. The critical parameters found for the bulk phase agree well with the theoretical critical index νth≅0.63 predicted by the 3D Ising model. As the crystal surface is approached, the critical parameter β increases to 0.51(2) but remains smaller than the value of β=0.8 for the surface of a semi-infinite Heisenberg model. Therefore, the effective dimensionality of the system, being equal to 3 in the bulk, decreases at the crystal surface.