¹Takaharu Saito,¹Hiroshi Hidaka,²Seung-Gu Lee
The Astrophysical Journal 877, 73 Link to Article [https://doi.org/10.3847/1538-4357/ab1aa5]
¹Department of Earth and Planetary Sciences, Nagoya University, Nagoya 464-8601, Japan
²Geological Research Division, Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Republic of Korea

Howardite–eucrite–diogenite meteorites are believed to originate in the crust of the asteroid 4 Vesta, whose differentiation processes are still controversial. In this study, the first 176Lu–176Hf isotopic data of nine diogenites are presented together with their 87Rb–87Sr isotopic compositions and rare earth element (REE) abundances to investigate the differentiation process of diogenites. The 176Lu–176Hf data sets of nine diogenites revealed the significantly higher initial 176Hf/177Hf ratio of diogenites than that of eucrites, while there are no resolvable differences between their ages. Based on the high initial ratio and the early formation of diogenites, their source material is estimated to be the Vestan mantle. The 87Rb–87Sr systematics of nine diogenites are entirely disturbed probably due to impact events on Vesta. The significant variation observed in the REE abundances of nine diogenites suggests their crystallization from compositionally diverse melts. Based on the mantle origin and compositional diversity of diogenites, we propose the crystallization of diogenites from partial melts of the Vestan mantle. The variation of the trace element abundances of diogenites can be explained by the variation of the degree of the partial melting. The timescale between the crystallization and partial melting of the Vestan mantle is estimated to be ~100–600 Ma from the 176Lu–176Hf isotopic data of nine diogenites, while a heat source for the partial melting is uncertain.

¹Bernd Helber,^1,2Bruno Dias,^1,3,4Federico Bariselli,¹Luiza F. Zavalan,⁵Lidia Pittarello,⁶Steven Goderis,⁶Bastien Soens,^6,7,8Seann J. McKibbin,⁶Philippe Claeys,¹Thierry E. Magin
The Astrophysical Journal 876, 120 Link to Article [https://doi.org/10.3847/1538-4357/ab16f0]
¹Aeronautics and Aerospace Department, von Karman Institute for Fluid Dynamics, Rhode-Saint-Genèse, Belgium
²Institute of Mechanics, Materials and Civil Engineering, Université catholique de Louvain, Louvain-la-Neuve, Belgium
³Research Group Electrochemical and Surface Engineering, Vrije Universiteit Brussel, Brussels, Belgium
⁴Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano, Milano, Italy
⁵Department of Lithospheric Research, University of Vienna, Vienna, Austria
⁶Analytical, Environmental, and Geo-Chemistry, Vrije Universiteit Brussel, Brussels, Belgium
⁷Institute of Earth and Environmental Science, University of Potsdam, Potsdam-Golm, Germany
⁸Geowissenschaftliches Zentrum, Georg-August-Universität Göttingen, Göttingen, Germany

Meteoroids largely disintegrate during their entry into the atmosphere, contributing significantly to the input of cosmic material to Earth. Yet, their atmospheric entry is not well understood. Experimental studies on meteoroid material degradation in high-enthalpy facilities are scarce and when the material is recovered after testing, it rarely provides sufficient quantitative data for the validation of simulation tools. In this work, we investigate the thermo-chemical degradation mechanism of a meteorite in a high-enthalpy ground facility able to reproduce atmospheric entry conditions. A testing methodology involving measurement techniques previously used for the characterization of thermal protection systems for spacecraft is adapted for the investigation of ablation of alkali basalt (employed here as meteorite analog) and ordinary chondrite samples. Both materials are exposed to a cold-wall stagnation point heat flux of 1.2 MW m−2. Numerous local pockets that formed on the surface of the samples by the emergence of gas bubbles reveal the frothing phenomenon characteristic of material degradation. Time-resolved optical emission spectroscopy data of ablated species allow us to identify the main radiating atoms and ions of potassium, calcium, magnesium, and iron. Surface temperature measurements provide maximum values of 2280 K for the basalt and 2360 K for the chondrite samples. We also develop a material response model by solving the heat conduction equation and accounting for evaporation and oxidation reaction processes in a 1D Cartesian domain. The simulation results are in good agreement with the data collected during the experiments, highlighting the importance of iron oxidation to the material degradation.

¹Gert Nolze,²Klaus Heide
Geochemistry (Chemie der Erde) (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.125538]
¹Dept 5.1, Federal Institute for Materials, Research and Testing (BAM), Unter den Eichen 87, 12205 Berlin, Germany
²Institut für Geowissenschaften (IGW), Friedrich-Schiller-Universität Jena (FSU), Germany
Copyright Elsevier

Roaldite – Fe4N – has been identified in the São Julião de Moreira iron meteorite using electron backscatter diffraction (EBSD) and simultaneously acquired energy-dispersive x-ray spectroscopy (EDS). Mean-periodic-number images derived from raw EBSD patterns confirm this phase by an even higher spatial resolution compared to EDS.
Roaldite appears in the form of systematically and repetitively aligned plates. Despite the locally heavy plastic deformation, it is shown that the origin of the oriented precipitation of roaldite is linked to the orientation of the kamacite matrix. Roaldite can be considered to be precipitated from kamacite using an inverse Kurdjumov-Sachs (K-S) or Nishiyama-Wassermann (N-W) orientation relationship. A more accurate discrimination is impossible due to the accumulated shock deformation, which blurs the local reference orientation of kamacite. The habit plane of roaldite is found to be {112}R, which is most likely parallel to {120}K of kamacite. Some of the roaldite plates contain two orientation variants which repeatedly alternate. Their misorientation angle is about 12°.

^1,2,3E.S.Steenstra,²J.Berndt, ¹S.Klemme,¹A.Rohrbach,¹E.S.Bullock,³W.van Westrenen
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.10.006]
¹The Geophysical Laboratory, Carnegie Institution of Science, Washington D.C., the United States of America
²Institute of Mineralogy, University of Münster, Germany
³Faculty of Science, Vrije Universiteit Amsterdam, The Netherlands
Copyright Elsevier

The geochemistry of asteroidal magmas provides fundamental clues to the processes involved in the origin and early evolution of planetary bodies. Although sulfides are important reservoirs for a diverse suite of major and trace elements, it is currently unclear whether the interiors of asteroid Vesta and the Angrite Parent Body were sulfide liquid saturated during petrogenesis of non-cumulate eucrites and volcanic angrites. To assess the potential of sulfide liquid saturation in the interiors of these bodies, high pressure (P) – temperature (T) experiments were used to quantify the sulfur concentrations at sulfide saturation (SCSS) for volcanic angrites and non-cumulate eucrites. The sulfide-silicate partitioning behavior of various trace elements was simultaneously quantified to study their geochemical behavior at sulfide liquid saturation.

It was found that the measured SCSS values agree well with the SCSS values predicted from a previous thermodynamic model for high-FeO* melts. To assess the possibility of sulfide liquid saturation of the source regions of non-cumulate eucrites and angrites, their S abundances were compared with the calculated SCSS values for their source regions. Results show that if eucritic and angritic source regions were saturated with FeS liquid, significant degassing (> 50–80%) of S must have occurred during or following their magmatic emplacement. Such loss is inconsistent with the S, Cl, Zn and Rb isotopic compositions of non-cumulate eucrites. Sulfide liquid saturation of eucrite and angrite source regions is also excluded from the strongly incompatible behavior of Cu and HSE in non-cumulate eucrites and angrites (Riches et al., 2012).

Additional calculations were performed to further explore the timing and extent of S loss during crystallization of the Vestan magma ocean. The assumption of chondritic bulk S abundances of bulk Vesta would correspond with extremely high S contents of the eucrite source region(s), even after consideration of depletion of S due to core formation. In light of the S, Cl, Zn and Rb stable isotopic compositions of eucrites, the S abundances in eucrites are most consistent with the hypothesis that the Vestan mantle was already strongly depleted in S (>70–80 %) by the time of Vestan magma ocean crystallization, resulting in more realistic S contents of the eucrite source region(s). The depletion of S could have been established during initial accretion of Vesta or it could simply reflect accretion of volatile depleted components that experienced incomplete condensation (Wu et al., 2018). Modeling of the new experimentally determined sulfide-silicate partition coefficients and previously reported Vestan mantle depletions of the various chalcophile and siderophile elements suggests that sulfide liquid segregation during early Vestan magma ocean crystallization is also unlikely. The lack of sulfide liquid saturation in the source regions of non-cumulate eucrites and angrites, as well as during early Vestan magma ocean solidification, shows that current geochemical models of core formation and late accretion remain valid for these bodies.

^1,2J. Chen,²B.L. Jolliff,²A. Wang,²R.L. Korotev,²K. Wang,²P.K. Carpenter,²H. Chen,¹Z. Ling,¹X. Fu,¹Y. Ni,¹H. Cao,¹Y. Huang
Journal of Geophysical Research , Planets  (in Press) Link to Article [https://doi.org/10.1029/2019JE006084]
¹Institute of Space Sciences, Shandong Provincial Key Laboratory of OpticaJ Astronomy and
Solar-TerrestriaJ Environment, Shandong University, Weihai 264209, China.
²Departrnent of Earth & Planetary Sciences and the McDonnell Center for the Space
Sciences, Washington University in St. Louis, MO 63130, USA.
²The Australian National Uruversity, Canberra ACT 2600, Australia.
Published by arrangement with John Wiley & Sons

We present comprehensive compositional and mineralogical results on two basaltic lunar meteorites Northwest Africa (NWA) 4734 and NWA 10597 to constrain their igneous mineralogy and metamorphic characteristics and examine the potential pairing relationship among them and other meteorites (e.g., basaltic lunar meteorites collected from LaPaz Icefield, Antarctica (LAPs)). NWA 4734 and NWA 10597 are low‐Ti (3.2–3.5 wt.% TiO₂), low‐Al (10–12 wt.% Al₂O₃), low‐K (880–1300 ppm K) mare basalts derived from evolved parental magma (Mg# (molar Mg/[Mg+Fe]×100) = 33.6–38.3) and are mostly composed of pyroxene (52.7–55.5 vol.%), plagioclase/maskelynite (27.5–29.3 vol.%), olivine (6.7–7.6 vol.%), and late‐formed components (i.e., mesostasis). Pyroxene and olivine in these two meteorites exhibit a multimodal compositional distribution, indicating multiple generations of these mafic minerals, which correspond to different evolution phases (e.g., magma chamber, ascending, and eruption) during the solidification of the basaltic parental magma. Immiscibility played an important role in the evolution of the late‐stage melts, inducing fractionation involving Fe‐rich and Si, K‐rich melts within mesostasis. Considering the extensive partial transformation of plagioclase to maskelynite across the sections, the average shock pressure endured by NWA 4734 and NWA 10597 is determined to be 23–29 GPa, which is consistent with the pressure condition (below 29.8 GPa) recorded by various silica polymorphs. Similar textures, bulk composition, modal mineral proportions, and mineral compositions indicate that NWA 4734, NWA 10597, and LAPs were most likely originated from the same region and both experienced intensive shock events after their crystallization.

¹Harries, D.
ACS Earth and Space Chemistry (in Press) Link to Article [DOI: 10.1021/acsearthspacechem.9b00081]
¹Institute of Geosciences, Friedrich Schiller University Jena, Carl-Zeiss-Promenade 10, Jena, 07745, Germany

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

^1,5,6Seann J. MCKIBBIN,^1,7Lidia PITTARELLO,¹Christina MAKARONA,^2,3
Christopher HAMANN,^2,3Lutz HECHT,^4,8Stepan M. CHERNONOZHKIN,¹Steven GODERIS,¹Philippe CLAEYS
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13392]
¹Analytical, Environmental and Geo-Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, Brussels 1050, Belgium
²Museum fur Naturkunde, Leibniz-Institut fur Evolutions- und Biodiversitatsforschung, Invalidenstraße 43,
10115 Berlin, Germany
³Institut fur Geologische Wissenschaften, Freie Universitat Berlin, Malteserstraße 74-100, 12249 Berlin, Germany
⁴GeoRessources, Faculte des Sciences et Technologies, Universite de Lorraine, Rue Jacques Callot, BP 70239, 54506,
Vandoeuvre-les-Nancy CEDEX, France
⁵Present address: Institut f€ur Erd- und Umweltwissenschaften, Universitat Potsdam, Haus 27, Karl-Liebknecht-Straße 24-25,
Potsdam-Golm 14476, Germany
⁶Present address: Geowissenschaftliches Zentrum, Abteilung Isotopengeologie, Georg-August-Universitat Göttingen,
Goldschmidtstraße 1, Göttingen 37073, Germany
⁷Present address: Department of Lithospheric Research, Universit€at Wien, UZA 2, Althanstraße 14, Vienna A-1090,Austria
⁸Department of Chemistry, Universiteit Gent, Krijgslaan 281-S12, Ghent 9000, BelgiumPresent address: Department of Chemistry, Universiteit Gent, Krijgslaan 281-S12, Ghent 9000, Belgium
Published by arrangement with John Wiley & Sons

Main group pallasite meteorites are samples of a single early magmatic planetesimal, dominated by metal and olivine but containing accessory chromite, sulfide, phosphide, phosphates, and rare phosphoran olivine. They represent mixtures of core and mantle materials, but the environment of formation is poorly understood, with a quiescent core–mantle boundary, violent core–mantle mixture, or surface mixture all recently suggested. Here, we review main group pallasite data sets and petrologic characteristics, and present new observations on the low‐MnO pallasite Brahin that contains abundant fragmental olivine, but also rounded and angular olivine and potential evidence of sulfide–phosphide liquid immiscibility. A reassessment of the literature shows that low‐MnO and high‐FeO subgroups preferentially host rounded olivine and low‐temperature P₂O₅‐rich phases such as the Mg‐phosphate farringtonite and phosphoran olivine. These phases form after metal and silicate reservoirs back‐react during decreasing temperature after initial separation, resulting in oxidation of phosphorus and chromium. Farringtonite and phosphoran olivine have not been found in the common subgroup PMG, which are mechanical mixtures of olivine, chromite with moderate Al₂O₃ contents, primitive solid metal, and evolved liquid metal. Lower concentrations of Mn in olivine of the low‐MnO PMG subgroup, and high concentrations of Mn in low‐Al₂O₃ chromites, trace the development and escape of sulfide‐rich melt in pallasites and the partially chalcophile behavior for Mn in this environment. Pallasites with rounded olivine indicate that the core–mantle boundary of their planetesimal may not be a simple interface but rather a volume in which interactions between metal, silicate, and other components occur.

¹Hoppe, P.,^2,4,5,6Pignatari, M.,³Amari, S.
Springer Proceedings in Physics 219, 373-376 Link to Article [DOI: 10.1007/978-3-030-13876-9_68]
¹Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, Mainz, 55128, Germany
²E. A. Milne Centre for Astrophysics, University of Hull, Hull, HU6 7RX, United Kingdom
³McDonnell Center for the Space Sciences and Physics Department, Washington University, St. Louis, MO 63130, United States
⁴NuGrid Collaboration, East Lansing, United States
⁵JINA-CEE, East Lansing, United States
⁶Konkoly Observatory, Konkoly Thege Miklos ut 15-17, Budapest, 1121, Hungary

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹E. A. MacLagan,^1,2E. L. Walton,¹C. D. K. Herd,¹B. Rivard
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13388]
¹Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, Alberta T6G 2E3, Canada
²Department of Physical Sciences, MacEwan University, City Centre Campus, 10700 104 Ave, Edmonton, Alberta T5J 4S2, Canada
Published by Arrangement with John Wiley and Sons

Hyperspectral imaging can be used to rapidly identify and map the spatial
distributions of many minerals. Here, hyperspectral mapping in three wavelength regions(visible and near-infrared, shortwave infrared, and thermal infrared) was applied to drill cores (ST001, ST002, and ST003) penetrating a continuous sequence of crater-fill breccias from the Steen River impact structure in Alberta, Canada. The combined data sets reveal distinct mineralogical layering, with breccias derived predominantly from sedimentary rocks overlying those derived from granitic basement. This stratigraphy demonstrates that the
breccias were not appreciably disturbed following deposition, which is inconsistent with formation models of similar breccias (suevites) by explosive impact melt–fluid interaction. At Steen River, volatiles from sedimentary target rocks were an inherent part of forming these enigmatic breccias. Approximately three quarters of terrestrial impact structures contain sedimentary target rocks; therefore, the role of volatiles in producing so-called
suevitic breccias may be more widespread than previously realized. The hyperspectral maps, specifically within the SWIR wavelength region, also delineate minerals associated with postimpact hydrothermal activity, including ammoniated clay and feldspar minerals not detectable using traditional techniques. These nitrogen-bearing minerals may have originated from microbial processes, associated with oil- and gas-producing units in the
crater vicinity. Such minerals may have important implications for the production of habitable environments by impact-induced hydrothermal activity on Earth and Mars.

¹B.L. Carrier,¹W.J. Abbey,¹L.W. Beegle,¹R. Bhartia,¹Y. Liu
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005758]
¹Jet Propulsion Laboratory, California Institute of Technology
Published by arrangement with John Wiley & Sons

The effects of radiation on the survivability of key biosignatures are a driving factor in exploration strategies throughout the solar system. Ultraviolet (UV) radiation, especially shorter wavelength UVC radiation, is known to be damaging to organisms and to potential organic biosignatures; however the interaction of UV radiation with minerals and rocks is not well understood. Constraining the survivability of organics and generation of habitable zones requires assessment of physical parameters such as penetration depth of UV photons. This type of information helps to identify to what extent rocks and minerals can provide effective shielding against UV radiation and is especially important on Mars where the surface chemistry is more oxidizing and the radiation environment is more extreme than on Earth. Using pressed pellets of natural gypsum, kaolinite, Mars simulant basalt and welded tuff, we measured the spectral transmittance of each in the wavelength range of 220‐400 nm. Although transmittance drops off quickly with depth, detectable levels of UV can penetrate >500 μm in each material. Each substrate allowed higher transmittance of UVC radiation than of longer wavelength UVA/B radiation, possibly as a result of surface reflectance and internal scattering properties. This could result in increased subsurface photolysis of organic compounds and biosignatures. We have used the transmittance data collected herein to constrain the lifetimes of several organic molecules in the Martian subsurface. These results will also have implications for organic analyses to be conducted by Mars 2020, and could be used to better constrain the SHERLOC/Mars 2020 interrogation volume.