Mid-infrared reflectance spectroscopy of synthetic glass analogs for mercury surface studies

Andreas Morlok, Christian Renggli, Bernard Charlier, Maximilian P. Reitze, Stephan Klemme, Olivier Namur, Martin Sohn, Dayl Martin, Iris Weber, Leksandra N.Stojic, Harald Hiesinger, Katherine H.Joy, Roy Wogelius, Peter Tollan, Cristian Carli, Karin E. Bauch, Joern Helbert

Available online 6 February 2021



• We synthesized glasses based on experiments of surface processes on Mercury.
• We obtained mid-infrared FTIR spectra for the comparison with spectra of Mercury.
• Results show Reststrahlenbands from 9.3 μm–9.9 μm, and CF from 7.6 μm–8.2 μm.
• Mg-rich glasses show similarity to hermean data, but more phases needed in mixture.
• Data will be used to interpret IR data from MERTIS on the BepiColombo mission.”

“We have synthesized and analyzed silicate glasses that are representative for the glasses on the surface of Mercury by mid-infrared reflectance spectroscopy, based on high-pressure laboratory experiments and the resulting compositions of the glass phase. The spectra are of interest for investigating the surface of Mercury using the MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) instrument on board of the ESA/JAXA BepiColombo mission.

Both powdered fractions and polished blocks have been analyzed. Powdered size fractions of 0–25 μm, 25-63 μm, 63-125 μm, and 125–250 μm were measured in reflectance in the thermal infrared (2–20 μm). Spectra for powdered bulk glasses (1.6 wt% – 19.0 wt% MgO) show a single, dominating Reststrahlenband (RB, 9.3–9.8 μm), a Christiansen Feature (CF; 7.6 μm – 8.1 μm), and a size dependent Transparency Feature (TF; 11.6–11.9 μm). Micro-FTIR analyses of polished blocks of glasses (3.4–26.5 wt% MgO) have characteristic bands at 7.8–8.2 μm (CF), and 9.3–9.9 μm (RB). Only few olivine crystalline features were observed.

Spectral features correlate with compositional characteristics, e.g. SiO2 content or SCFM (SiO2/(SiO2 + CaO + FeO + MgO) index. The strongest correlation between band features CF and the strong RB are with Mg/Si. No simple mixture of glass spectra from this study is able to reproduce the entire ground based spectrum of the surface of Mercury. However Mg-rich glasses reproduce identified features at 8.5 μm, 9.9 μm and 12.4 μm.”