Mössbauer and Raman spectroscopic in situ characterization of iron-bearing minerals in Mars: Exploration and cultural heritage

An increasing number of minerals have been described from the Martian surface in recent times. The Mössbauer spectrometers onboard the rovers Opportunity and Spirit have revealed the presence of several hydrous minerals. The development of these miniaturized analytical instruments represented a milestone for planetary research. Future missions to Mars such as EXOMARS 2018 and Mars 2020 will be equipped with miniaturized Raman spectrometers, intending to carry out an exhaustive mineralogical study of the Mars surface. Furthermore, detection of the presence of organic compounds related to present or ancient life on Mars will be addressed. Investigation of mineral formation, biogenesis and other water-related processes on Earth in similar conditions to those experienced in the past on Mars, is of considerable interest in relation to present and future Mars missions. Accordingly, the present work reviews some recent results obtained in the framework of several field expeditions to potential Mars analogue sites, mainly Rio Tinto and Jaroso Ravine in Spain by combining Mössbauer and Raman spectroscopies. The prototypes of the instruments used for Mars exploration can also be used in several other interesting terrestrial applications such as the investigation of cultural heritage. This is relevant because in many cases sampling and even physical contact is not possible and only techniques performing in situ and non-destructive analysis are allowed. Some examples are addressed in this work, including Roman and Greek artefacts and prehistoric rock art in caves of great importance, such as Altamira cave (northern Spain). The outcomes of these analyses demonstrate the advantages of these portable techniques in detecting, in situ, and in a totally non-destructive way, mineral phases, and in the case of Mössbauer, Fe-bearing minerals in particular.