Unraveling the true nature of Martian "LH-kieserite"

The exploration of our Solar system currently ranks among humanitys most exciting endeavors. The various strategies aiming to accomplish this feat include the reconnaissance of other planets and their moons, not only to investigate their surface topography, but also to assess the distribution and nature of local rocks and minerals, which in turn tells us more about the history of their formation and the processes having taken place on the particular celestial body. In this respect, the proven presence of various hydrated sulfate minerals is highly important. Not only do they contain significant amounts of chemically bound water, they also form part of its distribution cycle and even allow it to remain liquid below its usual freezing point, thus potentially enabling it to host primitive extraterrestrial life forms. For example, on the icy moons of Jupiter and Saturn the presence of sulfates often assists in maintaining a liquid ocean beneath their icy surface. On Mars, these minerals serve as storage of vast quantities of water and constitute part of the planetary water cycle. It is therefore of utmost relevance to unravel the true nature of the sulfates present on a given celestial body and to assess, in the laboratory, their chemical behavior. In course of a recently finished research project we now uncovered important hints about the potential presence of a hitherto overlooked group of magnesium sulfate minerals, summarily abbreviated MHSH, including the mysterious LH-kieserite, in our solar system. Their properties vary based on their water content as well as on chemical elements partially replacing magnesium, in turn leading to changes in their spectra and overall chemical behavior. If we could prepare MHSH and analyze these changes in detail here on Earth, such lab results would greatly assist the evaluation of measurements on other planets, currently attainable only in two ways by scanning of reflected spectra with orbiters or via direct measurements at the surface by current and upcoming rover missions, as is the case for Mars. Hence, the declared mission of our research project can be summarized as follows: 1) to refine the preliminary synthesis process for MHSH and fine-tune it for variations of the chemical composition as expected for planets and moons; 2) to investigate and document in detail the spectroscopic and crystallographic properties as a function of chemical composition, using infrared and Raman spectroscopy as well as X-ray diffraction; and 3) to perform these experiments also at low-temperature and high-pressure conditions relevant to the surface and interior of celestial bodies of our solar system. The obtained results will serve as a benchmark for comparison with data sent from Mars or the icy moons, enabling us to infer even the chemical composition of the material on the planets surface from infrared or Raman spectra.

Unraveling the true nature of Martian 'low-humidity-kieserite' The exploration of celestial bodies in our Solar system ranks among humanity's most exciting endeavors. Due to its high Earth-Similarity- and Planet-Habitability-Indices (ESI, PHI), Mars represents a primary target of international research efforts, using spectrometers on orbiters and sampling by Mars rovers to assess the distribution and nature of local rocks and minerals, which in turn tell us more about the history and processes of their formation. In particular, the presence of hydrated sulfate minerals attracts the attention since their discovery in Martian soils by the Viking landers in 1976. Since then, many studies confirmed the presence of sulfate-rich regions not only on Mars, but also on the icy moons of Jupiter and Saturn. These sulfates, among them the mineral kieserite, MgSO4H2O, contain significant amounts of water and constitute a relevant part of the Martian water cycle. In a solution, they allow it to remain liquid below its usual freezing point, and thus contribute to maintain liquid oceans beneath the surfaces of Jupiter's and Saturn's icy moons, representing potential hosts for primitive extraterrestrial life forms. It is therefore of highest importance to unravel the true nature of the sulfates present on these celestial bodies and to study the structural, spectroscopic, and chemical properties of their synthetic counterparts in laboratories on Earth. In our project we synthesized and studied a hitherto overlooked group of hydrated magnesium sulfate minerals, abbreviated 'MHSH'. Their properties change depending on their widely variable water content, in turn leading to changes in the spectra and chemical behavior. Our investigations of more than 100 group representatives also revealed that the mysterious Martian 'low-humidity kieserite' ('LH-kieserite') - a phase that has been controversially debated for almost 20 years - actually represents a member of this 'MHSH' group. While the aforementioned 'proper' kieserite, MgSO4H2O (studied in a previous project), allows the partial or even full replacement of Mg by cosmochemically relevant transition metals like Fe, Ni, Mn, or Co, compounds of the 'MHSH' group apparently do not incorporate other such elements (except Zn). Instead, synthesis runs aiming to replace Mg by Fe yielded the phase FeSO4OH as by-product. In collaboration with NASA and the SETI institute we could show that its spectral fingerprint matches certain spectral data from Mars that could not be assigned to any known mineral until then. Hence, with the results of our FWF-project we conclude that 1) 'MHSH' compounds with variable water content might play an important role for the sulfate assemblages on Mars, 2) the disputed and as yet quite mysterious Martian 'LH-kieserite' actually belongs to the 'MHSH' mineral group, and 3) FeSO4OH represents an important mineral on Mars, which has not been found on Earth so far.