¹Andreas Morlok, ¹Aleksandra Stojic, ²Isabelle Dittmar, ¹Harald Hiesinger, ¹Manuel Ahmedi, ²Martin Sohn, ¹Iris Weber, ³Joern Helbert 
¹Institut für Planetologie, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
²Hochschule Emden/Leer, Constantiaplatz 4, 26723 Emden, Germany
³Institute for Planetary Research, DLR, Rutherfordstrasse 2, 12489 Berlin, Germany

This study is part of an effort to build a mid-infrared database (7-14μm) of spectra for MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer), an instrument onboard of the ESA/JAXA BepiColombo space probe to be launched to Mercury in 2017.

Mercury was exposed to abundant impacts throughout its history. This study of terrestrial impactites can provide estimates of the effects of shock metamorphism on the mid-infrared spectral properties of planetary materials.

In this study, we focus on the Nördlinger Ries crater in Southern Germany, a well preserved and easily accessible impact crater with abundant suevite impactites. Suevite and melt glass bulk samples from Otting and Aumühle, as well as red suevite from Polsingen were characterized and their reflectance spectra in mid-infrared range obtained. In addition, in-situ mid-infrared spectra were made from glasses and matrix areas in thin sections. The results show similar, but distinguishable spectra for both bulk suevite and melt glass samples, as well as in-situ measurements.

Impact melt glass from Aumühle and Otting have spectra dominated by a Reststrahlen band at 9.3-9.6 μm. Bulk melt rock from Polsingen and bulk suevite and fine-grained matrix have their strongest band between 9.4 to 9.6 μm. There are also features between 8.5 and 9 μm, and 12.5 – 12.8 μm associated with crystalline phases. There is evidence of weathering products in the fine-grained matrix, such as smectites. Mercury endured many impacts with impactors of all sizes over its history. So spectral characteristics observed for impactites formed only in a single impact like in the Ries impact event can be expected to be very common on planetary bodies exposed to many more impacts in their past. We conclude that in mid-infrared remote sensing data the surface of Mercury can be expected to be dominated by features of amorphous materials.

Reference
Morlok A, Stojic A, Dittmar I, Hiesinger H, Ahmedi M, Sohn M, Weber I, Helbert J (2015) Mid-Infrared spectroscopy of impactites from the Nördlinger Ries impact crater. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.10.003]
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