1Andreas Morlok, 2Stephan Klemme, 1Iris Weber, 1Aleksandra Stojic, 3Martin Sohn, 1Harald Hiesinger
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.05.024]
1Institut für Planetologie, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
2Institut für Mineralogie, Corrensstraße 24, 48149 Münster, Germany
3Hochschule Emden/Leer, Constantiaplatz 4, 26723 Emden, Germany
In a study to provide ground-truth data for mid-infrared observations of the surface of Mercury with the MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) instrument onboard the ESA/JAXA BepiColombo mission, we have studied 17 synthetic glasses. These samples have the chemical compositions of characteristic Hermean surface areas based on MESSENGER data.
The samples have been characterized using optical microscopy, EMPA and Raman spectroscopy. Mid-infrared spectra have been obtained from polished thin sections using Micro-FTIR, and of powdered size fractions of bulk material (0-25, 25-63, 93-125 and 125-250 μm) in the 2.5-18 µm range.
The synthetic glasses display mostly spectra typical for amorphous materials with a dominating, single Reststrahlen Band (RB) at 9.5 µm – 10.7 µm. RB Features of crystalline forsterite are found in some cases at 9.5-10.2 µm, 10.4-11.2 µm, and at 11.9 µm. Dendritic crystallization starts at a MgO content higher than 23 wt.% MgO.
The Reststrahlen Bands, Christiansen Features (CF), and Transparency Features (TF) shift depending on the SiO2 and MgO contents. Also a shift of the Christiansen Feature of the glasses compared with the SCFM (SiO2/(SiO2+CaO+FeO+MgO)) index is observed. This shift could potentially help distinguish crystalline and amorphous material in remote sensing data. A comparison between the degree of polymerization of the glass and the width of the characteristic strong silicate feature shows a weak positive correlation.
A comparison with a high-quality mid-IR spectrum of Mercury shows some moderate similarity to the results of this study, but does not explain all features.