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]
Copyright Elsevier

¹Jamie E. Elsila, ¹Michael P. Callahan, ¹Jason P. Dworkin, ¹Daniel P. Glavin, ^1,2Hannah L. McLain, ^1,2Sarah K. Noble, ³Everett K. Gibson Jr.
¹NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
²Catholic University of America, Washington, DC 20064
³NASA Johnson Space Center, Houston, TX 77058

We analyzed the amino acid content of seven lunar regolith samples returned by the Apollo 16 and Apollo 17 missions and stored under NASA curation since collection using ultrahigh-performance liquid chromatography with fluorescence detection and time-of-flight mass spectrometry. Consistent with results from initial analyses shortly after collection in the 1970s, we observed amino acids at low concentrations in all of the curated samples, ranging from 0.2 parts-per-billion (ppb) to 42.7 ppb in hot-water extracts and 14.5 ppb to 651.1 ppb in 6M HCl acid-vapor-hydrolyzed, hot-water extracts. Amino acids identified in the Apollo soil extracts include glycine, d- and l-alanine, d- and l-aspartic acid, d- and l-glutamic acid, d- and l-serine, l-threonine, and l-valine, all of which had previously been detected in lunar samples, as well as several compounds not previously identified in lunar regoliths: α-aminoisobutyric acid (AIB), d- and l-β-amino-n-butyric acid (β-ABA), dl-α-amino-n-butyric acid, γ-amino-n-butyric acid, β-alanine, and ε-amino-n -caproic acid. We observed an excess of the l enantiomer in most of the detected proteinogenic amino acids, but racemic alanine and racemic β-ABA were present in some samples.

We also examined seven samples from Apollo 15, 16, and 17 that had been previously allocated to a non-curation laboratory, as well as two samples of terrestrial dunite from studies of lunar module engine exhaust that had been stored in the same laboratory. The amino acid content of these samples suggested that contamination had occurred during non-curatorial storage.

We measured the compound-specific carbon isotopic ratios of glycine, β-alanine, and l-alanine in Apollo regolith sample 70011 and found values of -21‰ to -33‰. These values are consistent with those seen in terrestrial biology and, together with the enantiomeric compositions of the proteinogenic amino acids, suggest that terrestrial biological contamination is a primary source of the amino acids in these samples. However, the presence of the non-proteinogenic amino acids such as AIB and β-ABA suggests the possibility of some contribution from exogenous sources.

We did not observe a correlation of amino acid content with proximity to the Apollo 17 lunar module, implying that lunar module exhaust was not a primary source of amino acid precursors. Solar-wind-implanted precursors such as HCN also appear to be at most a minor contributor, given a lack of correlation between amino acid content and soil maturity (as measured by Is/FeO ratio) and the differences between the δ13C values of the amino acids and the solar wind.

Reference
Elsila JE, Callahan MP, Dworkin JP, Glavin DP, McLain HL, Noble SK, Gibson Jr. EK (2015) The origin of amino acids in lunar regolith samples. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.10.008]
Copyright Elsevier