¹Iris Weber,¹Maximilian P. Reitze,¹Andreas Morlok,¹Aleksandra N. Stojic,¹Harald Hiesinger,¹Nico Schmedemann,¹Karin E. Bauch,¹Jan Hendrik Pasckert,²Jörn Helbert
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115683]
¹Institut für Planetologie (IfP), Westfälische Wilhelms-Universität, Wilhelm-Klemm-Str. 10, Münster 48149, Germany
²DLR, Institut für Planetenforschung, Rutherfordstr. 2, Berlin 12489, Germany
Copyright Elsevier

The behaviour of the Christiansen feature (CF) and the Reststrahlen bands (RBs) in mid-infrared (IR) reflectance spectra on various silicate mixtures as pressed pellets and powders was investigated in high-vacuum. In addition, the influence of micrometeorite bombardment simulated with an excimer laser was studied. The mixtures cover a wide range of possible hermean surface compositions and include the minerals olivine, pyroxene (enstatite and diopside), and plagioclase.

For the laser experiments, silicates were pressed into pellets and examined by reflectance infrared spectroscopy to identify changes caused by micrometeorite impacts as one tracer of space weathering on airless bodies such as Mercury. For comparison, measurements were also performed on loose powders with the same compositions under the same conditions. As a result, it can be shown that the RBs of olivine are rather affected by laser irradiation although SEM investigations show the destruction mainly of plagioclase, indicating that the RBs of plagioclase are masked by the “stronger” RBs of olivine and pyroxene. Furthermore, we found that the CF in mixtures with a plagioclase content of >50% does not shift significantly towards the CF of pyroxene or olivine. On the other hand, the CF of a mixture containing 50% olivine shifts significantly to shorter wavelengths when pyroxene or plagioclase are present in the mixture. Therefore, care is required when interpreting remote sensing data using the CF alone. We also found that the CF shifts to longer wavelengths in rough (regolithic) samples.

Our work demonstrates large dependencies of the CF and the RBs positions on the composition of the silicates as well as on the nature of the surface, which is important for space missions, e.g., data acquired by the MErcury Radiometer and Thermal Infrared Spectrometer (MERTIS) experiment onboard BepiColombo.

¹Adriana Pisarčíková,¹Pavol Matlovič,¹Juraj Tóth,²Stefan Loehle,³Ludovic Ferrière,²David Leiser,²Felix Grigat,⁴Jérémie Vaubaillon
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115682]
¹Faculty of Mathematics, Physics and Informatics, Comenius University in Bratislava, Slovakia
²High Enthalpy Flow Diagnostics Group, Institute of Space Systems, University of Stuttgart, Pfaffenwaldring 29, Stuttgart, 70569, Germany
³Natural History Museum Vienna, Burgring 7, Vienna, 1010, Austria
⁴IMCCE, Observatoire de Paris, PSL, 77 Av Denfert Rochereau, Paris, 75014, France
Copyright Elsevier

Fragments of small solar system bodies entering Earth’s atmosphere have possibly been important contributors of organic compounds to the early Earth. The cyano radical (CN) emission from meteors is considered as potentially one of the most suitable markers of organic compounds in meteoroids, however, its detection in meteor spectra has been thus far unsuccessful. With the aim to improve our abilities to identify CN emission in meteor observations and use its spectral features to characterize the composition of incoming asteroidal meteoroids, we present a detailed analysis of CN emission from high-resolution spectra of 22 laboratory simulated meteors including ordinary, carbonaceous, and enstatite chondrites, as well as a large diversity of achondrites (i.e., ureilite, aubrite, lunar, martian, howardite, eucrite, and diogenite), mesosiderite, and iron meteorites. We describe the variations of CN emission from different classes of asteroidal meteor analogues, its correlation and time evolution relative to other major meteoroid components. We demonstrate that CN can be used as a diagnostic spectral feature of carbonaceous and carbon-rich meteoroids, while most ordinary chondrites show no signs of CN. Our results point out strong correlation between CN and H emission and suggest both volatile features are suitable to trace contents of organic matter and water molecules present within meteoroids. For the application in lower resolution meteor observations, we demonstrate that CN can be best recognized in the early stages of ablation and for carbon-rich materials by measuring relative intensity ratio of CN band peak to the nearby Fe I-4 lines.