Extraterrestrial Mössbauer Spectroscopy

Abstract

To understand the origin of the Solar system and the origin of Life itself is one of the longest standing goals of human thought. Our Sun and its planets have formed out of an interstellar cloud which collapsed due to gravitational forces, forming a disk shaped so-called protosolar nebula, with the young star in the centre. Such disk shaped and dust grain containing protosolar nebulae have been observed. One of them is surrounding the young star Beta pictoris [1, 2]. Silicates, carbon and metal grains, oxides and sulfides should have been present. One of the important elements with relatively high abundance is iron. It is believed that simple molecules, such as water (H2O), carbon monoxide (CO), and hydrocarbons, were formed in this protosolar nebula [3]. As we know very well, at least in one case – our own Solar system – a variety of different objects were formed: planets, asteroids, and comets. At least on one of these planets, the Earth, life has formed. Today comets are believed to be remnants of the protosolar nebula, and the Sun and the planets are processed bodies, whereas asteroids are supposed to be only partially processed. The process of birth and evolution of our Solar system can be investigated indirectly by studying all the different members of the planetary system by means of remote sensing and planetary robotic space missions. One of the key elements in the evolution of the Solar system, and life itself, is iron. The chemistry of iron is strongly coupled to the chemistry of abundant elements as hydrogen, oxygen, and carbon. For instance, the oxidation state of iron in surface rocks of the planets is an important aspect because according to theoretical studies, iron contained in a planetary body should be the more oxidized the farther away from the sun this body has formed. By studying the cosmic history of iron, we have the possibility of understanding the chemical evolution of matter and life itself. Here, Mossbauer spectroscopy is the obvious tool, because it is a unique method for determining the oxidation state of the element iron, the mineralogical composition of iron containing rocks and their weathering products, meteorites and small grains from solid bodies, directly. This contributes to the understanding of the history and evolution of the planetary surfaces, for instance, the Martian surface, and their atmospheres.