Gas-solid reactions in hot, reduced planetary environments

Deutsche Forschungsgemeinschaft (DFG) - Project number 442083018

PI: Christian J. Renggli

The composition of planetary surfaces and crusts is strongly affected by the behavior of volatile and moderately volatile elements. Volatile elements become enriched in low-pressure environments by processes including degassing and volatilization of chemical elements, as well as reactions between gases and solids. One of the main properties affecting such gas-solid reactions is the oxidation state of the gas and these are poorly constrained at reducing conditions. In this research project, we will investigate the behavior of sulfur (S) and the metals zinc (Zn), copper (Cu) and iron (Fe) in gas-solid reactions under reducing conditions. The proposed experiments will simulate reduced fumarolic processes on the Moon and on Mercury for the first time. We will conduct laboratory experiments and analyze the obtained products regarding their mineralogy, and reaction induced effects on their isotopic signatures and fractionation behavior. There is currently no experimental data on the mineralogical and isotopic fractionation resulting from such gas-solid reactions. The obtained mineralogical and isotopic information is vital for the correct interpretation of the lunar Apollo samples, and will help in the preparation of future lunar missions and the understanding of their observations. Among the terrestrial planets, Mercury displays the most reducing surface conditions in the solar system, and the largest surface abundance of S (with up to 4wt%). Our experiments will investigate a possible formation mechanism for this atypical sulfur enrichment, a mechanism that is likely unique to the Solar System. We will characterize the experimentally obtained products not only regarding their isotopic composition and mineralogy, but also with infrared spectroscopy. Comparing these results with the data of the MERTIS spectrometer (Mercury Radiometer and Thermal Infrared Spectrometer), part of the scientific payload of the ESA/JAXA BepiColombo mission to Mercury (reaching Mercury in 2025), will allow to test our formation hypothesis of S-rich compounds on Mercury’s surface.