¹David L. Cook,²Ingo Leya,¹Maria Schönbächler
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13446]
¹Institute for Geochemistry and Petrology, ETH Zürich, Clausiusstrasse 25, 8092 Zürich, Switzerland
²Space Research and Planetology, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
Published by arrangement with John Wiley & Sons

We present model calculations for cosmogenic production rates in order to quantify the potential effects of spallation and neutron capture reactions on Fe and Ni isotopes in iron meteorites. We aim to determine whether the magnitude of any cosmogenic effects on the isotopic ratios of Fe and/or Ni may hinder the search for nucleosynthetic variations in these elements or in the application of the ⁶⁰Fe‐⁶⁰Ni chronometer. The model shows that neutron capture reactions are the dominant source of shifts in Fe and Ni isotopic ratios and that spallation reactions are mostly negligible. The effects on ⁶⁰Ni are sensitive to the Co/Ni ratio in the metal. The total galactic cosmic ray (GCR) effects on ⁶⁰Ni and ⁶⁴Ni can be minimized through the choice of normalizing isotopes (⁶¹Ni/⁵⁸Ni versus ⁶²Ni/⁵⁸Ni). In nearly all cases, the GCR effects (neutron capture and/or spallation) on Fe and Ni isotopic ratios are smaller than the current analytical resolution of the isotopic measurements. The model predictions are compared to the Fe and Ni isotopic compositions measured in a suite of six group IAB irons with a range of cosmic ray exposure histories. The experimental data are in good agreement with the model results. The minimal effects of GCRs on Fe and Ni isotopes should not hamper the search for nucleosynthetic variations in these two elements or the application of the ⁶⁰Fe‐⁶⁰Ni chronometer in iron meteorites or chondrites.

¹Pavel Spurný,¹Jiří Borovička,¹Lukáš Shrbený
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13444]
¹Astronomical Institute of the Czech Academy of Sciences, Fričova 298, 25165 Ondřejov Observatory, Czech Republic
Published by arrangement with John Wiley & Sons

We report a comprehensive analysis of the instrumentally observed meteorite fall Žďár nad Sázavou, which occurred in the Czech Republic on December 9, 2014, at 16:16:45–54 UT. The original meteoroid with an estimated initial mass of 150 kg entered the atmosphere with a speed of 21.89 km s⁻¹ and began a luminous trajectory at an altitude of 98.06 km. At the maximum, it reached −15.26 absolute magnitude and terminated after a 9.16 s and 170.5 km long flight at an altitude of 24.71 km with a speed of 4.8 km/s. The average slope of the atmospheric trajectory to the Earth’s surface was only 25.66°. Before its collision with Earth, the initial meteoroid orbited the Sun on a moderately eccentric orbit with perihelion near Venus orbit, aphelion in the outer main belt, and low inclination. During the atmospheric entry, the meteoroid severely fragmented at a very low dynamic pressure 0.016 MPa and further multiple fragmentations occurred at 1.4–2.5 MPa. Based on our analysis, so far three small meteorites classified as L3.9 ordinary chondrites totaling 87 g have been found almost exactly in the locations predicted for a given mass. Because of very high quality of photographic and radiometric records, taken by the dedicated instruments of the Czech part of the European Fireball Network, Žďár nad Sázavou belongs to the most reliably, accurately, and thoroughly described meteorite falls in history.

¹S.Potin,²S.Manigand,^1,3P.Beck,¹ C.Wolters,¹B.Schmitt
Icarus (in Press) Link to Aricle [https://doi.org/10.1016/j.icarus.2020.113686]
¹Université Grenoble Alpes, CNRS, IPAG, 414 rue de la Piscine, 38400 Saint-Martin d’Hères, France
²Niels Bohr Institute & Centre for Star and Planet Formation, University of Copenhagen, Øster Voldgade 5–7, DK-1350 Copenhagen K., Denmark
³Institut Universitaire de France, Paris, France
Copyright Elsevier

We present here a new method to model the shape of the 3-μm absorption band in the reflectance spectra of meteorites and small bodies. The band is decomposed into several OH/H2O components using Exponentially Modified Gaussian (EMG) profiles, as well as possible organic components using Gaussian profiles when present. We compare this model to polynomial and multiple Gaussian profile fits and show that the EMGs model returns the best rendering of the shape of the band, with significantly lower residuals. We also propose as an example an algorithm to estimate the error on the band parameters using a bootstrap method. We then present an application of the model to two spectral analyses of smectites subjected to different H2O vapor pressures, and present the variations of the components with decreasing humidity. This example emphasizes the ability of this model to coherently retrieve weak bands that are hidden within much stronger ones.

¹Wataru Fujiya,¹Yuto Aoki,²Takayuki Ushikubo,¹Ko Hashizume,³Akira Yamaguchi
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.02.003]
¹Faculty of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, 310-8512 Ibaraki, Japan
²Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, 200 Monobe-otsu, Nankoku, Kochi 783-8502, Japan
³National Institute for Polar Research, Midoricho10-3, Tachikawa, Tokyo 190-8518, Japan
Copyright Elsevier

We report the variability in carbon and oxygen isotopic compositions, chemical compositions, and cathodoluminescence intensities within calcite grains in the Yamato-791198 CM chondrite measured by secondary ion mass spectrometry. To understand the change in carbon isotopic compositions during calcite formation, the carbon isotope-analyses were performed on a series of crystal growth bands of each calcite grain. The crystal growth of calcite grains was inferred from comprehensive analyses of oxygen isotopes, chemical compositions, and cathodoluminescence characteristics.

The observed δ¹⁸O variations within individual grains are as large as 13‰. The oxygen-isotope data plot on a single straight line with a slope of 0.61 ± 0.06 (2σ) in an oxygen three-isotope diagram. This slope steeper than that of the terrestrial fractionation line indicates that the oxygen isotopic compositions of aqueous fluids evolved from higher δ¹⁸O and Δ¹⁷O to lower δ¹⁸O and Δ¹⁷O compositions due to the oxygen-isotope exchange between water and anhydrous silicates in the parent body. Thus, calcite crystals grew from higher Δ¹⁷O to lower Δ¹⁷O areas. The crystal growth inferred from oxygen isotopic compositions is corroborated by the morphology and cathodoluminescence characteristics of the calcite grains. The minor element concentrations of the calcite grains did not increase/decrease monotonically during calcite formation.

The δ¹³C variations within individual grains are no more than 4‰ except for one grain. The intra-grain δ¹³C variations observed here are much smaller than inter-grain δ¹³C variations of ∼80‰ previously reported. These observations indicate that the carbon isotopic compositions of dissolved carbon species did not change during calcite formation and that they were locally heterogeneous which reflects variable proportions of carbon reservoirs with different isotopic compositions.

¹Eniko R.Toth,¹Manuela A.Fehr,¹Matthias Friebel,¹Maria Schönbächler
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.01.059]
¹Institute of Geochemistry and Petrology, ETH Zürich, Clausiusstrasse 25, 8092 Zürich, Switzerland
Copyright Elsevier

Nucleosynthetic isotope variations are well documented for refractory elements in meteorites and the Earth, while moderately volatile elements generally display homogeneous compositions. Cadmium is a moderately volatile element with eight stable isotopes generated by a variety of nucleosynthetic processes. To address the extent of the nucleosynthetic variability in moderately volatile elements, new high precision Cd isotope data are presented for bulk samples of six carbonaceous and one enstatite chondrite. In addition, we report the first Cd isotope results of sequential acid leachates for the CM2 chondrite Jbilet Winselwan. Our new Cd data displays nucleosynthetic homogeneity for bulk chondrites and acid leachates within analytical uncertainties, in agreement with results for other moderately volatile elements. This implies that Cd isotopes were efficiently homogenised prior to incorporation into planetary bodies. We propose that Cd never significantly condensed into dust in stellar environments, or alternatively that such Cd-bearing dust was efficiently destroyed and recycled in the interstellar medium. Our leachate data provides evidence for further homogenisation during thermal processing in the protoplanetary disk including parent body processing. The data shows that Cd in carbonaceous chondrites mainly resides in the more easily dissolved phases, most likely sulphides that were affected by aqueous alteration. Less than 1% of the total Cd was recovered in the final leach fractions that employed HF and mainly dissolve silicates and refractory oxides.

Cadmium is susceptible to thermal neutron-capture effects due to the large neutron capture cross-section of ¹¹³Cd (∼20,000 barns). We report variations of up to −0.6 ± 0.3 for ε¹¹³Cd (internally normalised to ¹¹⁶Cd/¹¹¹Cd) in bulk chondrites, which renders Cd a potential thermal neutron-capture monitor. Most neutron dosimeters, such as Pt, Os and Hf, are sensitive to neutron capture in the epithermal energy range and have applications mainly limited to lunar samples or iron and stony-iron meteorites. The additional use of Cd, susceptible to neutron capture in the thermal energy range, therefore provides a new tool to determine the exposure histories of stony meteorites in more detail. Our study demonstrates that thermal neutron-capture effects in carbonaceous and enstatite chondrites can produce resolvable effects and require attention when assessing nucleosynthetic isotope variations.

^1,2Jianqing Feng,^1,2Matthew A. Siegler,³Paul O. Hayne
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2019JE006130]
¹Planetary Science Institute, Tucson, AZ, USA
²Roy M. Huffington Department of Earth Sciences, Southern Methodist University, Dallas, TX, USA
³Department of Astrophysical and Planetary Sciences and Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA
Published by arrangement with John Wiley & Sons

We derive a new constraint on the thermal and dielectric properties of the lunar regolith layer by reconciling data from the Lunar Reconnaissance Orbiter (LRO) Diviner infrared radiometer and Chang’E‐2 (CE‐2) microwave radiometer (MRM). The bolometric Bond albedo of the lunar surface, which characterizes the ability of the lunar surface to reflect visible radiation, is a function of incidence angle. We determined the Bond albedo by using the Lunar Orbiter Laser Altimeter 1,064‐nm normal albedo and the surface temperature at noon as a function of latitude. The results suggest a modification to existing regolith thermal conductivity models based on a fit to the diurnal variation of Diviner data. Based on the thermal model, a 1‐D radiative transfer and dielectric properties model is developed to fit MRM data for the global Moon. With a new dielectric loss tangent equation for highland regolith applied, our model matches MRM data well at 19.35 and 37 GHz, which are generally accepted to be well calibrated. A global map of loss tangent of the Moon at these frequencies is also obtained by fitting the diurnal amplitude of microwave brightness temperature (TB) of each location on the Moon. We find that the loss tangent of highlands regolith has a slight frequency dependence and is larger than previous studies. We also identify a large discrepancy between our theoretical model and TB obtained by CE‐2 MRM at low frequencies, which is attributed to issues caused by contamination on calibration horn.

^1,2Jennika Greer,²Surya. S. Rout,^3,4Dieter Isheim,^3,4David N. Seidman,⁵Rainer Wieler,^1,2Philipp R. Heck
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13443]
¹Department of the Geophysical Sciences, The University of Chicago, Chicago, Illinois, 60637 USA
²Robert A. Pritzker Center for Meteoritics and Polar Studies, Field Museum of Natural History, Chicago, Illinois, 60605 USA
³Northwestern Center for Atom Probe Tomography (NUCAPT), Northwestern University, Evanston, Illinois 60208, USA
⁴Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois, 60208 USA
⁵Institute of Geochemistry and Petrology, ETH Zürich, Zürich, Switzerland
Published by arrangement with John Wiley & Sons

The surfaces of airless bodies, such as the Moon and asteroids, are subject to space weathering, which alters the mineralogy of the upper tens of nanometers of grain surfaces. Atom probe tomography (APT) has the appropriate 3‐D spatial resolution and analytical sensitivity to investigate such features at the nanometer scale. Here, we demonstrate that APT can be successfully used to characterize the composition and texture of space weathering products in ilmenite from Apollo 17 sample 71501 at near‐atomic resolution. Two of the studied nanotips sampled the top surface of the space‐weathered grain, while another nanotip sampled the ilmenite at about 50 nm below the surface. These nanotips contain small nanophase Fe particles (~3 to 10 nm diameter), with these particles becoming less frequent with depth. One of the nanotips contains a sequence of space weathering products, compositional zoning, and a void space (~15 nm in diameter) which we interpret as a vesicle generated by solar wind irradiation. No noble gases were detected in this vesicle, although there is evidence for ⁴He elsewhere in the nanotip. This lunar soil grain exhibits the same space weathering features that have been well documented in transmission electron microscope studies of lunar and Itokawa asteroidal regolith grains.

¹Johnson, D.,²Tyldesley, J.
Mummies, magic and medicine in ancient Egypt (Book Chapter) Link to Article [ISBN: 978-178499750-2;978-178499243-9]
¹The Department of Physical Sciences, The Open University, United Kingdom
²The University of Manchester, United Kingdom

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^1,2Louisa J. Preston,^2,3Rebeca Barcenilla,³Lewis R. Dartnell,⁴Ezgi Kucukkilic-Stephens,⁴Karen Olsson-Francis
Astrobiology 20, Link to Article [https://doi.org/10.1089/ast.2019.2106]
¹Department of Earth Sciences, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK
²Department of Earth and Planetary Sciences, Birkbeck College, University of London, London, UK.
³Department of Life Sciences, University of Westminster, London, UK.
⁴Department of EEES, The Open University, Walton Hall, Milton Keynes, UK.

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^1,2Lidia Pittarello,^3,4Joerg Fritz,¹Julia Roszjar,⁵Christoph Lenz,⁵Chutimun Chanmuang N.,^1,2Christian Koeberl
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13445]
¹Natural History Museum Vienna, Burgring 7, A‐1010 Vienna, Austria
²Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A‐1090 Vienna, Austria
³Saalbau Weltraum Projekt, Liebigstrasse 6, D‐64646 Heppenheim, Germany
⁴Zentrum für Rieskrater‐ und Impaktforschung Nördlingen (ZERIN), Vordere Gerbergasse 3, D‐86720 Nördlingen, Germany
⁵Institut für Mineralogie und Kristallographie, University of Vienna, Althanstrasse 14, A‐1090 Vienna, Austria
Published by arrangement with John Wiley & Sons

Shock amorphization of plagioclase, from partial to complete, has been used to evaluate the degree of shock in meteorites. Important information on the shock amplitude can be derived from the measurement of the refractive index in plagioclase, either from mineral separates or in petrographic thin sections. However, this technique is time‐consuming, and associated sample preparations are considered destructive and are not always possible for precious and rare meteorite samples. In addition, plagioclase amorphization is commonly inhomogeneous at the sample scale and a statistically meaningful number of grains must be considered. Here, we apply several nondestructive spectroscopic techniques, such as Raman spectroscopy, photoluminescence, and cathodoluminescence, to plagioclase experimentally shocked at 28 GPa, and thus in the transition regime between crystalline plagioclase and fully amorphous material. Most of the plagioclase was transformed into diaplectic glass at 28 GPa, yet some grains exhibit heterogeneously distributed crystalline domains. This confirms that intrinsic and extrinsic factors lead to local variations in the intensity of the shock pressure within individual plagioclase crystals of homogeneous composition. The amorphization of plagioclase can qualitatively (and potentially also quantitatively) be investigated by spectroscopic techniques, highlighting such local variations in the shock efficiency.