The Advanced Miniaturised Mössbauer Spectrometer MIMOS IIa. A Portable Instrument for the In Situ Investigation of Fe-Bearing Mineralogy and Elemental Composition

Two miniaturized Mössbauer spectrometers MIMOS II as part of the NASA Mars Exploration Rover mission have been operating on the surface of Mars for more than four years now. Their results proved vital in the search for signs of past water on Mars and in the assessment of past habitability. Advanced versions of these Mössbauer spectrometers are also part of future space missions such as the Russian Phobos Grunt, a sample return mission to Mars' moon Phobos, and the European Space Agency's ExoMars rover, an exo/astrobiological mission to the Red Planet.

Mössbauer spectroscopy can determine the quantitative speciation of Fe among its oxidation and coordination states, and Fe-bearing mineral phases. The advanced MIMOS IIa is portable and set up in backscattering geometry, rendering sample preparation unnecessary. The instrument is further reduced in mass. It uses Silicon Drift Detectors (SDD) instead of Si-PIN diodes. The SDDs provide a higher energy resolution and as a result an approximately tenfold better signal-to-noise ratio. This decreases measurement times significantly from several hours down to 10s of minutes. The SDDs also allow for the acquisition of X-ray fluorescence spectra and therefore the investigation of elemental composition. For terrestrial applications, where mass is not such an issue, internal shielding can be added which makes the instrument with its 57Co source safer to handle in the field or in the lab.