^1,2Bethany L. Ehlmann, ²Robert Hodyss, ³Thomas F. Bristow, ¹George R. Rossman, ^4,5Eleonora Ammannito M., ⁶Cristina De Sanctis, ⁵Carol A. Raymond
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13103]
¹Division of Geological & Planetary Sciences, California Institute of Technology, Pasadena, California, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
³Exobiology Branch, NASA Ames Research Center, Moffett Field, California, USA
⁴Department of Earth Planetary and Space Sciences, University of California, Los Angeles, California, USA
⁵Italian Space Agency (ASI), , Rome, Italy
⁶Istituto di Astrofisica e Planetologia Spaziali, Istituto Nazionale di Astrofisica, , Rome, Italy
Published by arrangement with John Wiley & Sons

Mg‐phyllosilicate‐bearing, dark surface materials on the dwarf planet Ceres have NH4‐bearing materials, indicated by a distinctive 3.06 μm absorption feature. To constrain the identity of the Ceres NH4‐carrier phase(s), we ammoniated ground particulates of candidate materials to compare their spectral properties to infrared data acquired by Dawn’s Visible and Infrared (VIR) imaging spectrometer. We treated Mg‐, Fe‐, and Al‐smectite clay minerals; Mg‐serpentines; Mg‐chlorite; and a suite of carbonaceous meteorites with NH4‐acetate to exchange ammonium. Serpentines and chlorites showed no evidence for ammoniation, as expected due to their lack of exchangeable interlayer sites. Most smectites showed evidence for ammoniation by incorporation of NH4+ into their interlayers, resulting in the appearance of absorptions from 3.02 to 3.08 μm. Meteorite samples tested had weak absorptions between 3.0 and 3.1 μm but showed little clear evidence for enhancement upon ammoniation, likely due to the high proportion of serpentine and other minerals relative to expandable smectite phases or to NH4+ complexing with organics or other constituents. The wavelength position of the smectite NH4 absorption showed no variation between IR spectra acquired under dry‐air purge at 25 °C and under vacuum at 25 °C to −180 °C. Collectively, data from the smectite samples show that the precise center wavelength of the characteristic ~3.05 μm v3 absorption in NH4 is variable and is likely related to the degree of hydrogen bonding of NH4‐H2O complexes. Comparison with Dawn VIR spectra indicates that the hypothesis of Mg‐saponite as the ammonium carrier phase is the simplest explanation for observed data, and that Ceres dark materials may be like Cold Bokkeveld or Tagish Lake but with proportionally more Mg‐smectite.

¹Rona Oran, ¹Benjamin P. Weiss, ²Ofer Cohen
Earth and Planetary Science Letters 492, 222-231 Link to Article [https://doi.org/10.1016/j.epsl.2018.02.013]
¹Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
²Lowell Center for Space Science and Technology, University of Massachusetts, Lowell, MA 01854, USA
Copyright Elsevier

Chondritic meteorites have been traditionally thought to be samples of undifferentiated bodies that never experienced large-scale melting. This view has been challenged by the existence of post-accretional, unidirectional natural remanent magnetization (NRM) in CV carbonaceous chondrites. The relatively young inferred NRM age [∼10 million years (My) after solar system formation] and long duration of NRM acquisition (1–10⁶ y) have been interpreted as evidence that the magnetizing field was that of a core dynamo within the CV parent body. This would imply that CV chondrites represent the primitive crust of a partially differentiated body. However, an alternative hypothesis is that the NRM was imparted by the early solar wind. Here we demonstrate that the solar wind scenario is unlikely due to three main factors: 1) the magnitude of the early solar wind magnetic field is estimated to be <0.1 μT in the terrestrial planet-forming region, 2) the resistivity of chondritic bodies limits field amplification due to pile-up of the solar wind to less than a factor of 3.5 times that of the instantaneous solar wind field, and 3) the solar wind field likely changed over timescales orders of magnitude shorter than the timescale of NRM acquisition. Using analytical arguments, numerical simulations and astronomical observations of the present-day solar wind and magnetic fields of young stars, we show that the maximum mean field the ancient solar wind could have imparted on an undifferentiated CV parent body is <3.5 nT, which is 3–4 and 3 orders of magnitude weaker than the paleointensities recorded by the CV chondrites Allende and Kaba, respectively. Therefore, the solar wind is highly unlikely to be the source of the NRM in CV chondrites. Nevertheless, future high sensitivity paleomagnetic studies of rapidly-cooled meteorites with high magnetic recording fidelity could potentially trace the evolution of the solar wind field in time.

¹Mehmet Yesiltas
Spectrochmica Acta Part A: Molecular and Biomolecular Spectroscopy 194, 92-101 Link to Article [https://doi.org/10.1016/j.saa.2018.01.021]
¹Faculty of Aeronautics and Space Sciences, Kirklareli University, Kirklareli 39000, Turkey

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¹A.A.Maksimova,¹M.I.Oshtrakha,¹A.V.Chukina,²I.Felner,¹G.A.Yakovlev,¹V.A.Semionkin
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 192, 275-284 Link to Article [https://doi.org/10.1016/j.saa.2017.10.056]
¹Institute of Physics and Technology, Ural Federal University, Ekaterinburg 620002, Russian Federation
²Racah Institute of Physics, The Hebrew University, Jerusalem, Israel

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^1,2Farhang Nabiei, ¹James Badro, ^2,5Teresa Dennenwaldt, ²Emad Oveisi, ²Marco Cantoni, ^2,5Cécile Hébert, ⁶Ahmed El Goresy, ⁷Jean-Alix Barrat, ¹Philippe Gillet
Nature Communications 9, 1327 Link to Article [doi:10.1038/s41467-018-03808-6]
¹Earth and Planetary Science Laboratory (EPSL), Institute of Physics, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
²Interdisciplinary Center for Electron Microscopy (CIME), Ecole ³Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
⁴Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Paris, France
⁵Electron Spectrometry and Microscopy Laboratory (LSME), Institute of Physics, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
⁶Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth, Germany
⁷Institut Universitaire Européen de la Mer, Université de Bretagne Occidentale, Plouzané, France

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¹Knut Metzler
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13091]
¹Institut für Planetologie, Westfälische Wilhelms‐Universität Münster, , Münster, Germany
Published by arrangement with John Wiley & Sons

In order to characterize the relation between apparent chondrule sizes (2D) and true chondrule sizes (3D), three ordinary chondrites of the H, L, and LL group have been analyzed. The diameters of a large number of chondrule cut faces in thin sections (2D; n = 2037) and of separated chondrules from the same meteorites (3D: n = 2061) have been measured. The obtained 2D/3D mean chondrule sizes (μm) for the H, L, and LL chondrite are 450/490, 500/610, and 690/830; the corresponding median values (μm) are 370/420, 450/530, and 580/730. The data show that there is a cutoff for small chondrule sizes in each sample. Possibly characteristic minimum sizes exist for the various groups, increasing in the (3D) sequence H (~90 μm) <L (~180 μm) <LL (~240 μm). No systematics were found for the maximum chondrule sizes. The investigated samples show very similar chondrule volume (mass) distributions relative to the mode (peak) of their size‐frequency distributions. About 2.6–2.9% and 97.1–97.4% of the total chondrule volume (mass) is present in chondrule sizes smaller and larger than the mode, respectively. It was found that 2D sectioning consistently results in a shift of the true 3D size‐frequency distributions toward smaller sizes. This effect leads to the underestimation of the values for (1) the true mean chondrule size by 8–18%, (2) the true chondrule median value by 12–21%, and (3) the true mode value of the size‐frequency distributions by 12–17% (50 μm binning). This is the opposite of what popular 2D/3D correction models predict (e.g., Eisenhour 1996).

¹Alexander Hubbard, ¹Mordecai‐Mark Mac Low, ²Denton S. Ebel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13101]
¹Department of Astrophysics, American Museum of Natural History, New York, New York, USA
²Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA
Published by arrangement with John Wiley & Sons

Meteoritical and astrophysical models of planet formation make contradictory predictions for dust concentration factors in chondrule‐forming regions of the solar nebula. Meteoritical and cosmochemical models strongly suggest that chondrules, a key component of the meteoritical record, formed in regions with solids‐to‐gas mass ratios orders above the solar nebula average. However, models of dust grain dynamics in protoplanetary disks struggle to surpass concentration factors of a few except during very short‐lived stages in a dust grain’s life. Worse, those models do not predict significant concentration factors for dust grains the size of chondrule precursors. We briefly develop the difficulty in concentrating dust particles in the context of nebular chondrule formation and show that the disagreement is sufficiently stark that cosmochemists should explore ideas that might revise the concentration factor requirements downward.

¹Rebecca Winkler, ²Robert Luther, ¹Michael H. Poelchau, ²Kai Wünnemann, ¹Thomas Kenkmann
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13080]
¹Institute of Earth and Environmental Sciences—Geology, Albert‐Ludwigs‐Universität Freiburg (ALU), , Freiburg, Germany
²Museum für Naturkunde Berlin, Leibniz Institute for Evolution and Biodiversity Science, , Berlin, Germany
Published by arrangement with John Wiley and Sons

Two impact cratering experiments on nonporous rock targets were carried out to determine the influence of target composition on the structural mechanisms of subsurface deformation. Projectiles of 2.5 mm diameter were accelerated to ~5 km s⁻¹and impacted onto blocks of marble or quartzite. Subsurface deformation was mapped and analyzed on the microscale using thin sections of the bisected craters. Additionally, both experiments were modeled and the calculated strain zones underneath the craters were compared to experimental deformation features. Microanalysis shows that the formation of radial, tensile, and intragranular cracks is a common response of both nonporous materials to impact cratering. In the quartzite target, the subsurface damage is additionally characterized by highly localized deformation along shear bands with intense grain comminution, surrounded by damage zones. In contrast, the marble target shows closely spaced calcite twinning and cleavage activation. Crater diameter and depth as well as the damage lens underneath the crater are unexpectedly smaller in the marble target compared to the quartzite target, which is in contradiction to the marble’s much weaker compressive and tensile strengths. However, numerical models result in craters that are similar in size as well as in strain accumulation at the end of transient crater formation, indicating that current models should still be viewed cautiously when compared to experimental details.

¹J. F. Rapp,²D. S. Draper
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13086]
¹Jacobs JETS, NASA Johnson Space Center, Houston, Texas, USA
²Astromaterials Research Office, EISD, NASA Johnson Space Center, Houston, Texas, USA
Published by arrangement with John Wiley & Sons

We report results of systematic experimental simulation of fractional crystallization of a lunar magma ocean (LMO) with the Lunar Primitive Upper Mantle bulk composition. These results complement prior work that simulated equilibrium crystallization. In contrast to previous numerical models for investigating magma ocean solidification processes and implications, our combined program simulates these processes directly using petrologic experimentation. Our experiments mimic LMO crystallization that is fractional throughout the process, rather than switching from initially equilibrium to fractional crystallization partway through. To do this, we adopted an iterative approach in which the starting material for each run is synthesized using the composition of the melt phase from the prior run. We compare our results to those from long‐standing numerical models of LMO crystallization and show that although some features of those models are broadly reproduced, there are key differences in liquid lines of descent and the cumulate lithologies generated. Our results can be used to estimate the possible thickness of a primordial lunar crust formed from flotation of plagioclase during magma ocean solidification. Our estimate is greater than that from the recent Gravity Recovery and Interior Laboratory (GRAIL) mission, but consistent with the criteria on which the starting bulk composition was originally calculated. It assumes perfectly efficient separation of all plagioclase formed from the crystallizing magma ocean, which is likely not the case. We also demonstrate that a non‐chondritic bulk composition, with respect to trace elements, is not required in order to generate a KREEP (potassium, rare earth elements, and phosphorus) signature from magma ocean crystallization.

^1,2Masahiro Kayama,^3,4Toshimori Sekine,⁵Naotaka Tomioka,⁶Hirotsugu Nishido,³Yukako Kato,⁶Kiyotaka Ninagawa,⁷Takamichi Kobayashi,^8,9Akira Yamaguchi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13092]
¹Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, Sendai, Japan
²Creative Interdisciplinary Research Division, Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai, Japan
³Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, Higashi‐Hiroshima, Japan
⁴Center for High Pressure Science and Technology Advanced Research, , Shanghai, China
⁵Kochi Institute for Core Sample Research, Japan Agency for Marine‐Earth Science and Technology, , Nankoku City, Kochi, Japan
⁶Department of Biosphere‐Geosphere Science, Okayama University of Science, , Okayama, Japan
⁷National Institute for Materials Science, , Tsukuba, Ibaraki, Japan
⁸National Institute of Polar Research, Tachikawa, Tokyo, Japan
⁹Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Hayama, Tokyo, Japan
Published by arrangement with John Wiley & Sons

Cathodoluminescence (CL) analyses were carried out on maskelynite and lingunite in L6 chondrites of Tenham and Yamato‐790729. Under CL microscopy, bright blue emission was observed in Na‐lingunite in the shock veins. Dull blue‐emitting maskelynite is adjacent to the shock veins, and aqua blue luminescent plagioclase lies farther away. CL spectroscopy of the Na‐lingunite showed emission bands centered at ~330, 360–380, and ~590 nm. CL spectra of maskelynite consisted of emission bands at ~330 and ~380 nm. Only an emission band at 420 nm was recognized in crystalline plagioclase. Deconvolution of CL spectra from maskelynite successfully separated the UV–blue emission bands into Gaussian components at 3.88, 3.26, and 2.95 eV. For comparison, we prepared K‐lingunite and experimentally shock‐recovered feldspars at the known shock pressures of 11.1–41.2 GPa to measure CL spectra. Synthetic K‐lingunite has similar UV–blue and characteristic yellow bands at ~550, ~660, ~720, ~750, and ~770 nm. The UV–blue emissions of shock‐recovered feldspars and the diaplectic feldspar glasses show a good correlation between intensity and shock pressure after deconvolution. They may be assigned to pressure‐induced defects in Si and Al octahedra and tetrahedra. The components at 3.88 and 3.26 eV were detectable in the lingunite, both of which may be caused by the defects in Si and Al octahedra, the same as maskelynite. CL of maskelynite and lingunite may be applicable to estimate shock pressure for feldspar‐bearing meteorites, impactites, and samples returned by spacecraft mission, although we need to develop more as a reliable shock barometer.