¹M. Patzek, ¹A. Bischoff, ²R. Visser, ²T. John
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13175]
¹Institut für Planetologie, Westfälische Wilhelms‐Universität Münster, Münster, Germany
²Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstr. 74‐100, Berlin, Germany
Published by arrangement with John Wiley & Sons

Meteoritic breccias are valuable samples as they can contain rare materials from the early solar system as clasts. Volatile‐rich, CI‐ and CM‐like clasts may represent parent body lithologies, which cannot be found as individual meteorites in today’s meteorite collections. In order to reveal a better knowledge about the presence and chemical characteristics and variability of volatile (water‐bearing) materials in the early solar system these clasts play an important role. Such materials may have been available as the volatile component during the accretion of terrestrial planets. To understand the distribution of volatile‐rich materials in the solar system, we studied CI‐ and CM‐like clasts in brecciated meteorites including polymict ureilites, HEDs, CR, CB, CH, and ordinary chondrites. CI‐like clasts occur throughout all of the mentioned meteorite groups, whereas the CM‐like clasts have only been identified in HEDs and ordinary chondrites. The abundance of volatile‐rich clasts in general decreases in the order CH > CR > ureilites > HEDs > CB > OC > R. The mineralogy of CI‐like clasts is similar to CI chondrites, but their compositions of phyllosilicates differ. The mineralogy of CM‐like clasts clearly links them to CM chondrites. They must have been delivered to the HED parent body by low‐velocity impacts after differentiation and volcanism, as there is no evidence for high shock and heating processes. Additionally, we propose that CI‐like clasts in the CR, CB, and CH chondrites are a primary component of the appropriate parent bodies (accretionary breccias). Conversely, the CI‐like clasts in polymict ureilites and HEDs represent an infall as (micro)meteorites or as low‐velocity impactors, which happened after the accretion and differentiation of the appropriate parent bodies.

^1,2Ninja Braukmüller, ^1,2Frank Wombacher, ^1,3Dominik C.Hezel, ^1,2Raphaelle Escoube, ^1,2Carsten Münker
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.07.023]
¹Institut für Geologie und Mineralogie, Universität zu Köln, Zülpicher Str. 49b, 50674 Köln, Germany
²Steinmann Institut für Geologie, Mineralogie und Paläontologie, Universität Bonn, Poppelsdorfer Schloss, 53115 Bonn, Germany
³Natural History Museum, Department of Mineralogy, Cromwell Road, SW7 5BD, London, UK
Copyright Elsevier

In Earth and planetary sciences, the chemical composition of chondritic meteorites provides an essential reference to constrain the composition and differentiation history of planetary reservoirs. Yet, for many trace elements, and in particular for volatile trace elements the composition of chondrites is not well constrained. Here we present new compositional data for carbonaceous chondrites with an emphasis on the origin of the volatile element depletion pattern. Our database includes 25 carbonaceous chondrites from 6 different groups (CI, CM, CR, CV, CO, CK), two ungrouped carbonaceous chondrites and Murchison powder samples heated up to 1000°C in O₂ or Ar gas streams, respectively. A total of 51 major and trace elements were analyzed by sector field inductively coupled plasma mass spectrometry (SF-ICP-MS), using chondrite-matched calibration solutions. Our results confirm that parent body alteration and terrestrial weathering only have minor effects on the bulk chondrite compositions. Thermal metamorphism can lead to the loss of some volatile elements, as best observed in the heating experiments and two thermally overprinted chondrites Y-980115 (CI) and EET 96026 (CV4/5 or CK4/5). The effects of aqueous alteration and terrestrial weathering on the Antarctic samples are difficult to discriminate. Both processes may redistribute fluid mobile elements such as K, Na, Rb, U and LREE within the meteorite. In hot desert finds, the typical weathering effects are enrichments of Sr, Ba and U and a depletion of S.

In general, moderately volatile elements with 50% condensation temperatures (T_C) ranging from 1250 K to 800 K show an increasing depletion, whereas 11 moderately volatile elements with 50% T_C between 800 K and 500 K are unfractionated from each other in most samples. Their extent of depletion is characteristic for the different chondrite groups. Because of this well-defined “hockey stick” pattern, we propose to divide the moderately volatile elements into two subgroups, the ‘slope volatile elements’ and the unfractionated ‘plateau volatile elements’ with lower T_C. Notably, the abundances of plateau volatile elements exhibit a co-variation with the matrix abundances of the respective host meteorites. Carbonaceous chondrite matrices are likely mixes of: (i) CI-like material and (ii) chondrule-related matrix. Chondrule-related matrix is expected to be depleted in volatile elements relative to CI and likely formed contemporaneously with chondrules, leading to chondrule-matrix complementarity. The addition of CI-like material only changed the absolute elemental concentrations of bulk matrix and bulk chondrite, while refractory and main component element ratios such as Mg/Si remain unaffected. Such a model can also account for the co-existence of low temperature CI-like material and high temperature chondrule and chondrule-related matrix. However, elevated volatile element abundances observed in chondrules still provide a challenge for the model as proposed here.

¹Mamta Chauhan, ²Satadru Bhattacharya, ^1,2Sumit Pathak, ³Prakash Chauhan
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13176]
¹Department of Geology, School of Earth Sciences, Banasthali Vidyapith, Rajasthan, India
²Space Applications Centre, Indian Space Research Organization, Ahmedabad, Gujarat, India
³Indian Institute of Remote Sensing, Dehradun, Uttarakhand, India
Published by arrangement with John Wiley & Sons

The Hansteen‐Billy region of the Moon lying toward the southwest edge of Oceanus Procellarum is characterized by emplacement of three different aged basaltic units viz. INm, Im, and Em. The present study primarily utilizes high‐resolution Chandrayaan‐I, Moon Mineralogy Mapper (M3) data clipped at ~2.5 μm for mineral analysis of these units. The spectra of all the three regions show two prominent absorption bands. Spectral analysis characterizes the earliest INm basalts as low‐Ca pyroxenes with large band area ratios (BAR) and nearly similar B‐I and B‐II strength. The Em and Im basalts are Ca and high‐Ca pyroxenes, respectively, with relatively less BAR values and more B‐II/B‐I strength. The relative content of their spectra after olivine correction appears to be dominated by pyroxene. The obtained results have been used for estimation of the compositional characteristics of pyroxenes from laboratory‐based calibration equations. The pyroxene composition for INm basalts indicates their pigeonitic affinity, whereas the Im and Em basalts is close to augite. The estimated temperature of crystallization suggests that basalts in this region evolved at higher temperature and are preserved in a metastable condition due to quick cooling. Furthermore, the area is characterized by increase in concentration of both the Fe and Ti with age as assessed from Clementine mineral map. The obtained results have been discussed in relation with source of the magma.

¹Samuel Ebert, ¹Jan Render, ¹Gregory A.Brennecka,¹Christoph Burkhardt, ¹Addi Bischoff, ¹Simone Gerber, ¹Thorsten Kleine
Earth & Planetary Science Letters 498, 257-265 Link to Article [https://doi.org/10.1016/j.epsl.2018.06.040]
¹Institut für Planetologie, University of Münster, Wilhelm Klemm-Straße 10, 48149 Münster, Germany
Copyright Elsevier

Understanding the relationships between and among chondritic components of various chondrite groups is of prime importance for deciphering the dynamics of material transport and planetary accretion in the early Solar System. Here we obtain insights into these processes and the reservoirs present by investigating the nucleosynthetic Ti isotopic signatures of individual Ca,Al-rich inclusions (CAIs) and Na–Al-rich chondrules from ordinary and CO chondrites. This specific type of chondrule is of interest as it is thought to have incorporated refractory, CAI-like material as precursors. Our data show that CAIs from ordinary and CO chondrites exhibit 50Ti excesses that are indistinguishable from CV CAIs, and thus indicate a common source reservoir for refractory inclusions in ordinary, CO, and CV chondrites. Na–Al-rich chondrules from CO chondrites also show 50Ti excesses, indicating the presence of CAIs from this reservoir in the precursor materials of CO chondrules. In contrast, Na–Al-rich chondrules from ordinary chondrites show no 50Ti excesses and are indistinguishable from the bulk values for ordinary chondrites. Thus, known CAIs cannot have been the refractory precursor of the Na–Al-rich chondrules in ordinary chondrites. Consequently, within the accretion region of the ordinary chondrites, two different types of refractory components must have existed: (1) a 50Ti-enriched refractory component that is present as CAIs and either arrived at the accretion region of the ordinary chondrites after chondrule formation, or was only present in insignificant amounts, and (2) another type of refractory material without a 50Ti excess, which was involved as precursor in the chondrule formation process. Our data thus imply that refractory components with condensation signatures must have formed in at least two isotopically distinct nebular regions. These may be related to non-carbonaceous and carbonaceous source regions, that is, the inner and outer Solar System, divided by the early formation of Jupiter.

¹Addi Bischoff, ^1,2Maximilian Schleiting, ³Rainer Wieler, ¹Markus Patzek
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.07.020]
¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, D-48149 Münster, Germany
²Institut für konstruktiven Ingenieurbau, Universität Kassel, Mönchebergstr. 7, D-34125 Kassel, Germany
³ETH Zürich, Departement Erdwissenschaften, Clausiusstr. 25, CH-8092 Zürich, Switzerland
Copyright Elsevier

After accretion of meteorite parent bodies, larger and smaller collisions have led to significant modifications of these bodies. Involved processes include excavation of material, thermal metamorphism, melting, mixing of different materials, re-accretion, and re-lithification. All these processes can be repeated several times. In this study polished thin sections (PTS) of 2280 chondrites (1193 H, 947 L, and 140 LL chondrites) were investigated in order to obtain the abundance of brecciated rocks among the ordinary chondrites. In addition, we have determined the abundance and characteristics of shock vein-bearing H, L, and LL chondrites and of impact melt rock clasts. We also recognized xenolithic components based on O-isotope studies. Noble gas data were considered in order to detect regolith breccias and to discuss late impact histories. The investigation of 2280 samples shows that 23% (276 of 1193) of the H chondrites, 23% (220 of 947) of the L chondrites, and 79 % (110 of 140) of the LL chondrites are brecciated. Considering the heavily-brecciated LL chondrites in 63 of the 140 chondrites (45%) shock veins were clearly detected. 57 of these 63 chondrites are brecciated rocks. The investigation of the H and L chondrites has shown that about 26% (310 of 1193) of the H chondrites and 40% (379 of 947) of the L chondrites contain shock veins. In our data-set 20% of the H chondrites and 8.3% of the LL chondrites, but only 3.0% of the L chondrites contain solar noble gases. Remarkably, about 62% of all brecciated H chondrites (with noble gases analyzed) contain solar noble gases compared to only around 11% and 10% of the brecciated L and LL chondrites, respectively. The identification of xenolithic clasts (e.g., CI-, CM-, and ureilite-like lithologies) in primitive type 3 chondrites indicates simultaneous accretion of clasts and chondrules. These clasts must have been formed early within the first 2 Ma on subsequently-destroyed precursor, first generation parent bodies. The formation of complex breccias witnesses the collisions between asteroids of very different lithologies and heritage. Although the onion-shell configuration of primordial parent bodies is necessary in order to form the chondrites with different degrees of metamorphic overprint (petrologic types 3-6) subsequent catastrophic fragmentation and reassembly to form asteroids with a rubble-pile structure are required to explain certain features discussed in this work. However, distinct peaks in the cosmic ray exposure age distributions indicate that not too many impacts in the last 100 Ma were responsible to deliver the majority of the ordinary chondritic meteoroids to Earth. Yet, this certainly does not tell anything about the number of “last-generation” parent bodies that exist in the asteroid belt, since S-type asteroids are the most abundant type of asteroid in the inner main belt and thought to be the parent bodies of ordinary chondrites.

¹Kyusei Tsuno, ¹Damanveer S.Grewal, ¹Rajdeep Dasgupta
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.07.010]
¹Department of Earth, Environmental, and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, TX 77005, USA
Copyright Elsevier

Constraining carbon (C) fractionation between silicate magma ocean (MO) and core-forming alloy liquid during early differentiation is essential to understand the origin and early distribution of C between reservoirs such as the crust-atmosphere, mantle, and core of Earth and other terrestrial planets. Yet experimental data at high pressure (P)-temperature (T) on the effect of other light elements such as sulfur (S) in alloy liquid on alloy-silicate partitioning of C and C solubility in Fe-alloy compositions relevant for core formation is lacking. Here we have performed multi-anvil experiments at 6–13 GPa and 1800–2000 °C to examine the effects of S and Ni on the solubility limit of C in Fe-rich alloy liquid as well as partitioning behavior of C between alloy liquid and silicate melt (DCalloy/silicate). The results show that C solubility in the alloy liquid as well as DCalloy/silicate decreases with increasing in S content in the alloy liquid. Empirical regression on C solubility in alloy liquid using our new experimental data and previous experiments demonstrates that C solubility significantly increases with increasing temperature, whereas unlike in S-poor or S-free alloy compositions, there is no discernible effect of Ni on C solubility in S-rich alloy liquid.

Our modelling results confirm previous findings that in order to satisfy the C budget of BSE, the bulk Earth C undergoing alloy-silicate fractionation needs to be as high as those of CI-type carbonaceous chondrite, i.e., not leaving any room for volatility-induced loss of carbon during accretion. For Mars, on the other hand, an average single-stage core formation at relatively oxidized conditions (1.0 log unit below IW buffer) with 10-16 wt.% S in the core could yield a Martian mantle with a C budget similar to that of Earth’s BSE for a bulk C content of ∼0.25-0.9 wt.%. For the scenario where C was delivered to the proto-Earth by a S-rich differentiated impactor at a later stage, our model calculations predict that bulk C content in the impactor can be as low as ∼0.5 wt.% for an impactor mass that lies between 9-20% of present day Earth’s mass. This value is much higher than 0.05-0.1 wt.% bulk C in the impactor predicted by Li et al. (2016) because C-solubility limit of 0.3 wt.% in a S-rich alloy predicted by their models is significantly lower than the experimentally derived C-solubility of ∼1.6 wt. % for the relevant S-content in the core of the impactor.

¹Robert Luther, ^1,2Meng‐Hua Zhu, ³Gareth Collins, ^1,4Kai Wünnemann
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13143]
¹Museum für Naturkunde Berlin, Leibniz Institute for Evolution and Biodiversity ScienceBerlin, Germany
²Space Science Institute, Macau University of Science and TechnologyTaipa, Macau
³Department of Earth Science & Engineering, Imperial College LondonLondon, UK
⁴Institute of Geological Sciences, Freie Universität BerlinBerlin, Germany
Published by arrangement with John Wiley & Sons

Impact craters are formed by the displacement and ejection of target material. Ejection angles and speeds during the excavation process depend on specific target properties. In order to quantify the influence of the constitutive properties of the target and impact velocity on ejection trajectories, we present the results of a systematic numerical parameter study. We have carried out a suite of numerical simulations of impact scenarios with different coefficients of friction (0.0–1.0), porosities (0–42%), and cohesions (0–150 MPa). Furthermore, simulations with varying pairs of impact velocity (1–20 km s⁻¹) and projectile mass yielding craters of approximately equal volume are examined. We record ejection speed, ejection angle, and the mass of ejected material to determine parameters in scaling relationships, and to calculate the thickness of deposited ejecta by assuming analytical parabolic trajectories under Earth gravity. For the resulting deposits, we parameterize the thickness as a function of radial distance by a power law. We find that strength—that is, the coefficient of friction and target cohesion—has the strongest effect on the distribution of ejecta. In contrast, ejecta thickness as a function of distance is very similar for different target porosities and for varying impact velocities larger than ~6 km s⁻¹. We compare the derived ejecta deposits with observations from natural craters and experiments.

¹N.H.Thomas et al. (>10)
Journal of Geophysical Research Planets (in Press) Link to Article [https://doi.org/10.1029/2017JE005467]
¹Division of Geological and Planetary Sciences, California Institute of TechnologyPasadena, California, USA
Published by arrangement with John Wiley & Sons

The Mars Science Laboratory rover, Curiosity, is equipped with ChemCam, a Laser‐Induced Breakdown Spectroscopy (LIBS) instrument, to determine the elemental composition of nearby targets quickly and remotely. We use a laboratory sample set including prepared mixtures of basalt with systematic variation in hydrated mineral content and compositionally well‐characterized, altered basaltic volcanic rocks to measure hydrogen by characterizing the H‐alpha emission line in LIBS spectra under martian environmental conditions. The H contents of all samples were independently measured using thermogravimetric analysis. We found that H peak area increases with weight percent H for our laboratory mixtures with basaltic matrices. The increase is linear with weight percent H in the mixtures with structurally bound H up to about 1.25 wt. % H and then steepens for higher H‐content samples, a non‐linear trend not previously reported but potentially important for characterizing high water content materials. To compensate for instrument, environmental, and target matrix related effects on quantification of H content from the LIBS signal, we examined multiple normalization methods. The best performing methods utilize O 778 nm and C 248 nm emission lines. The methods return comparable results when applied to ChemCam data of H‐bearing materials on Mars. The calibration and normalization methods tested here will aid in investigations of H by LIBS on Mars with ChemCam and SuperCam. Further laboratory work will aid quantification across different physical matrices and heterogeneous textures because of differences we observed in H in pelletized and natural rock samples of the same composition.

^1,2Peter Jennikens et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13137]
¹SETI Institute, Carl Sagan CenterMountain View, California, USA
²NASA Ames Research CenterMoffett Field, California, USA
Published by arrangement with John Wiley & Sons

Bolides are detected by the Geostationary Lightning Mapper onboard the GOES‐16 weather satellite, which takes images of Earth at a rate of 500 Hz in a 1.1 nm wide pass band centered on 777.4 nm wavelength. Ten case studies are discussed. These initial results were obtained using the Level 0 data received during the nonoperational in‐orbit postlaunch test period. GLM positions and timings are sufficiently accurate to assist in trajectory and orbit reconstruction. GLM samples the light curve nearly completely, unaffected by onboard and downlink processes tailored to lightning data. Sufficient data on the instantaneous background scene are provided to reconstruct the baseline drift in the brightest pixels. The agreement to within a factor of 2–3 between measured total radiated energy from GLM and that derived from other space‐borne observations implies that during the bolide’s peak brightness the GLM pass band is dominated by continuum emission, rather than O I line emission. The reported flux is corrected for angle‐from‐nadir shifts in the central wavelength of the pass band, which overestimates continuum flux by only up to 20% for most of the GLM field of view, but more so if the bolide is observed far from nadir. Assuming a 6000 K blackbody spectrum, GLM is able to detect bolides with peak visual magnitude (at a normalized 100 km distance) brighter than about −14 in nighttime, and slightly brighter in daytime.

^1,2Mutsumi Komatsu, ²Timothy J. Fagan, ³Alexander N. Krot, ³Kazuhide Nagashima, ^4,5Michail I. Petaev, ^6,7Makoto Kimura, ^6,8Akira Yamaguchi
Proceedings of the National Academy of Sciences of the United States of America
Link to Article [https://doi.org/10.1073/pnas.1722265115]
¹The Graduate University for Advanced Studies (SOKENDAI), Hayama, 240-0193 Kanagawa, Japan
²Department of Earth Sciences, Waseda University, Shinjuku, 169-8050 Tokyo, Japan
³Hawai‘i Institute of Geophysics and Planetology, School of Ocean, Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI 96822
⁴Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138
⁵Harvard–Smithsonian Center for Astrophysics, Cambridge, MA 02138
⁶National Institute of Polar Research, Tachikawa, 190-8518 Tokyo, Japan
⁷Ibaraki University, 310-8512 Mito, Japan
⁸Department of Polar Science, School of Multidisciplinary Science, SOKENDAI, Tachikawa, 190-8518 Tokyo, Japan

Calcium-aluminum–rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs), a refractory component of chondritic meteorites, formed in a high-temperature region of the protoplanetary disk characterized by approximately solar chemical and oxygen isotopic (Δ¹⁷O ∼ −24‰) compositions, most likely near the protosun. Here we describe a ¹⁶O-rich (Δ¹⁷O ∼ −22 ± 2‰) AOA from the carbonaceous Renazzo-type (CR) chondrite Yamato-793261 containing both (i) an ultrarefractory CAI and (ii) forsterite, low-Ca pyroxene, and silica, indicating formation by gas–solid reactions over a wide temperature range from ∼1,800 to ∼1,150 K. This AOA provides direct evidence for gas–solid condensation of silica in a CAI/AOA-forming region. In a gas of solar composition, the Mg/Si ratio exceeds 1, and, therefore, silica is not predicted to condense under equilibrium conditions, suggesting that the AOA formed in a parcel of gas with fractionated Mg/Si ratio, most likely due to condensation of forsterite grains. Thermodynamic modeling suggests that silica formed by condensation of nebular gas depleted by ∼10× in H and He that cooled at 50 K/hour at total pressure of 10⁻⁴ bar. Condensation of silica from a hot, chemically fractionated gas could explain the origin of silica identified from infrared spectroscopy of remote protostellar disks.