^1,2M.J.Loeffler,³B.S.Prince
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.114881]
¹Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, AZ 86011, United States of America
²Center for Materials Interfaces in Research and Applications, Northern Arizona University, Flagstaff, AZ 86011, United States of America
³Department of Applied Physics and Materials Science, Northern Arizona University, Flagstaff, AZ 86011, United States of America
Copyright Elsevier

In an effort to better understand the role dark material plays in the reflectance spectrum of carbonaceous asteroids, we performed laboratory studies focusing on quantifying how the addition of relevant dark material (graphite, magnetite and troilite) can alter the ultraviolet-visible and near-infrared spectrum of a neutral silicate mineral. We find that addition of graphite, magnetite and troilite all darken the reflectance spectrum of our forsterite samples and cause the spectral slope to decrease (become blue). These spectral changes can be caused by both nm- and μm-sized grains. In the ultraviolet-visible region, we find that graphite is most efficient at altering the spectral slope, while in the near-infrared, magnetite is the most efficient. At all wavelengths studied, graphite is the most efficient at darkening our sample spectrum. However, the observation that troilite also alters the slope and albedo of our samples suggests that the spectral changes caused by magnetite and graphite may not be unique. In addition, we find that the spectral slopes in our mixtures compare generally well to what has been observed on Bennu suggesting that a significant portion of fine-grained dark material, including sulfides, present in the regolith can cause the observed negative (blue) slope found on B-type asteroids.

¹Addi Bischoff,¹Jakob Storz,^2,3Jean-Alix Barrat,⁴Dieter Heinlein,^5,6A. J. Timothy Jull,^7,8Silke Merchel,⁹Andreas Pack,⁷Georg Rugel
Meteorotics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13779]
¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm Str. 10, Münster, D-48149 Germany
²CNRS, IRD, Ifremer, LEMAR, University of Brest, Plouzané, F-29280 France
³Institut Universitaire de France, Paris, 75005 France
⁴German Fireball Network, Lilienstraße 3, Augsburg, D-86156 Germany
⁵University of Arizona AMS Laboratory, 1118 East Fourth St, Tucson, Arizona, 85721 USA
⁶Isotope Climatology and Environmental Research Centre (ICER), Institute for Nuclear Research, Hungarian Academy of Sciences, Bem ter 18/c, Debrecen, 4026 Hungary
⁷Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, Dresden, D-01328 Germany
⁸Faculty of Physics, Isotope Physics, VERA Laboratory, University of Vienna, Währinger Str. 17, Vienna, 1090 Austria
⁹Geowissenschaftliches Zentrum, Universität Göttingen, Goldschmidtstr. 1, Göttingen, D-37077 Germany
Published by Arrangement with John Wiley & Sons

In the last 7 years, three meteorites (Blaubeuren, Cloppenburg, and Machtenstein) found in Germany were identified as chondrites. Two of these rocks had been recovered from the impact sites decades ago but not considered to be meteorites. The aim of this study is to fully characterize these three meteorites. Based on the compositional data on the silicates, namely olivine and low-Ca pyroxene, these meteorites fit nicely within the H-group ordinary chondrites. The brecciated texture of Blaubeuren and Cloppenburg (both H4-5) is perfectly visible, whereas that of Machtenstein, officially classified as an H5 chondrite, is less obvious but was detected and described in this study. Considering chondrites in general, brecciated rocks are very common rather than an exception. The bulk rock degree of shock is S2 for Blaubeuren and Machtenstein and S3 for Cloppenburg. All samples show significant features of weathering. They have lost their original fusion crust and more than half (W3) or about half (W2-3) of their original metal abundances. The oxygen isotope compositions of the three chondrites are consistent with those of other H chondrites; however, the Cloppenburg values are heavily disturbed and influenced by terrestrial weathering. This is supported by the occurrence of the very rare hydrated iron phosphate mineral vivianite (Fe2+Fe2+2[PO4]2·8H2O), which indicates that the chondrite was weathered in a very wet environment. The terrestrial ages of Blaubeuren (~9.2 ka), Cloppenburg (~5.4 ka), and Machtenstein (~1.8 ka) show that these chondrites are very similar in their degree of alteration and terrestrial age compared to meteorite finds from relatively wet terrestrial environments. They still contain abundant metal, although, as noted, the oxygen isotope data indicate substantial weathering of Cloppenburg. The bulk compositions of the three meteorites are typical for H chondrites, although terrestrial alteration has slightly modified the concentrations, leading in general to a loss of Fe, Co, and Ni due to preferential alteration of metals and sulfides. As exceptions, Co and Ni concentrations in Machtenstein, which has the shortest terrestrial age, are typical for H chondrites. The chemical data show no enrichments in Ba and Sr, as is often observed in different meteorite groups of desert finds.