Dr. Christian Josef Renggli

High-temperature gas-solid reactions in plenetary environments

My research focuses on how high-temperature gas-rock interactions alter the surfaces, crusts, and the regolith of terrestrial planetary bodies. Direct sampling of volcanic or fumarolic gases in planetary environments is impossible, either because of extreme conditions such as on the Jupiter moon Io, or on Venus, or because volcanic activity has stopped billions of years ago, such as on the Moon or on Mercury. Experimental approaches are an important alternative to explore these processes in the laboratory and constrain planetary volatile budgets. I am currently funded through my DFG project “Gas-solid reactions in hot, reduced planetary environments” (project 442083018). In this project I study the behavior of S-rich volcanic and fumarolic gases at reducing conditions on the Moon and on Mercury.

Sulfur on Mercury

One of my current research interests is the question, what processes lead to the extreme enrichment of S on the surface of Mercury? I use silica glass tube experiments to investigate sulfidation processes under Mercury conditions that may be responsible for the enrichment of sulfur on the planets’ surface (up to 4 wt.%) (Weider et al., 2015; Mccoy et al., 2018; Nittler et al., 2018). By using graphite crucibles, gas-solid reactions can be conducted at reducing conditions that have been inferred for volcanic processes on Mercury. In an ongoing collaboration with the team of the ESA BepiColombo mid-infrared spectrometry instrument MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) at the Institut für Planetologie, Universität Münster, we use these experimental run products as reference materials for the observations expected from Mercury, allowing us to test the sulfidation hypothesis.

Element volatilization

An important research interest is in the speciation and volatilization behavior of chemical elements in volcanic gas phases (Renggli et al., 2017), and the volatilization from silicate melts. Within the framework of the SFB-TRR 170 “late accretion onto terrestrial planets” collaborative research center, funded by the German Research Foundation, I am an associate member and work with PhD candidates to study the effect of Cl and S on the volatilization of Zn, Cu and Ge, and the associated stable isotope fractionation. Additionally, we investigate the degassing and isotopic fraction of S and Te as a function of oxygen fugacity and temperature. Furthermore, we study the degassing of volatile and moderately volatile elements from metallic melts, to constrain their depletion in group IVB iron meteorites (Campbell and Humayun, 2005). These experiments will help us constrain the budget of late accreted materials and the earliest stages of planet formation.