^1,4L.Nardi, ^1,2E.Palomba, ^1,3A.Longobardo, ^1,5A.Galiano, ¹F.Dirri
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.10.035]
¹INAF-IAPS, Via Fosso del Cavaliere 100, Roma 00133, Italy
²ASI-SSDC, via del Politecnico, Roma 00133, Italy
³Università Parthenope, Dist. Centro Direzionale Isola C4, 80143, Italy
⁴La Sapienza Università di Roma, Piazzale Aldo Moro 5, Roma 00185, Italy
⁵Università degli Studi di Roma Tor Vergata, Via Orazio Raimondo 18, Roma 00173, Italy
Copyright Elsevier

Olivine is one of the main abundant mineral in the Solar System, and the determination of its abundance on a surface may give fundamental information about its evolution. The study of surface distribution of olivine on asteroid (25143) Itokawa through near-Infrared reflectance spectroscopy is a difficult goal because olivine and pyroxene bands centred at 1 μm and 2 μm are not entirely included in Hayabusa/NIRS’ spectral range. In this work, the retrieval of olivine abundance has been performed by applying two different methods: the first one uses some spectral indices to retrieve olivine abundance, whilst the second one consists of the application of the Hapke’s theory in order to create synthetic spectra aimed at fitting a selection of NIRS’ spectra. The analysis performed with the first method brought to an approximately homogeneous distribution of olivine content (60  ±  15% on average) on Itokawa’s surface, with the exception of Sagamihara region, which has a slightly (up to 10%) lower olivine content. The second method brought to an average 60  ±  7.5% olivine content within 5 selected spectra, with the same reduction found in the spectrum from the Sagamihara region. All these values are in agreement with literature values on this topic, especially with the ones retrieved from particles sampled in Muses Sea by the Hayabusa probe.

¹Wen Xiang Xia et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.10.031]
¹Hubei Subsurface Multi-scale Imaging Key Laboratory, Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan, 430074, China
Copyright Elsevier

The major oxides (SiO2, Al2O3, CaO, FeO, MgO, and TiO2) and Mg# are critical for revealing the petrological characteristics of the Moon and for testing models of lunar formation and geologic evolution. There are few high-spatial-resolution (<250 m/pixel) abundance maps for all the six major oxides and Mg# across the Moon. Furthermore, previous studies primarily employed the traditional regression methods to derive oxide contents from optical images, which may influence the inversion accuracies of the lunar chemical compositions. This paper reports the abundance maps of all the six major oxides and Mg# with a high spatial resolution of ∼200 m/pixel and compared them with the ones in the previous works. Neural networks algorithms along with the data from the Interference Imaging Spectrometer (IIM) onboard Chang’E-1 were employed in this paper to derive the abundances of the six oxides. Compared with the traditional linear regression models, the neural networks method suggested in this work is hopeful to better depict the complex nonlinear relations between the spectra and the chemical components, so it may improve the inversion performance of the lunar chemistry.

^1,2Sune G.Nielsen,¹Maureen Auro,³Kevin Righter,⁴David Davis,^5,6Julie Prytulak,⁷Fei Wu,⁷Jeremy D.Owens
Earth and Planetary Science Letters 505, 131-140 Link to Article [https://doi.org/10.1016/j.epsl.2018.10.029]
¹NIRVANA Laboratories, Woods Hole Oceanographic Institution, Woods Hole, MA, USA
²Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, USA
³NASA JSC, Houston, TX, USA
⁴Department of Earth Science, Georgia State University, Atlanta, GA, USA
⁵Department of Earth Science and Engineering, Imperial College London, UK
⁶Department of Earth Science, Durham University, UK
⁷Department of Earth, Ocean and Atmospheric Science, National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32306, USA
Copyright Elsevier

Vanadium (V) isotopes have been hypothesized to record irradiation processes in the early solar system through production of the minor 50V isotope. However, because V only possesses two stable isotopes it is difficult to distinguish irradiation from other processes such as stable isotope fractionation and nucleosynthetic heterogeneity that could also cause V isotope variation. Here we perform the first detailed investigation of V isotopes in ordinary and carbonaceous chondrites to investigate the origin of any variation. We also perform a three-laboratory inter-calibration for chondrites, which confirms that the different chemical separation protocols do not induce V isotope analytical artifacts as long as samples are measured using medium resolution multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS). Vanadium isotope compositions (51V/50V) of carbonaceous chondrites correlate with previously reported nucleosynthetically derived excesses in 54Cr. Both 51V and 54Cr are the most neutron-rich of their respective elements, which may suggest that pre-solar grains rich in r-process isotopes is the primary cause of the V–Cr isotope correlation. Vanadium isotope ratios of ordinary chondrite groups and Earth form a weaker correlation with 54Cr that has a different slope than observed for carbonaceous chondrites. The offset between carbonaceous and non-carbonaceous meteorites in V–Cr isotope space is similar to differences also reported for chromium, titanium, oxygen, molybdenum and ruthenium isotopes, which has been inferred to reflect the presence in the early solar system of two physically separated reservoirs. The V isotope composition of Earth is heavier than any meteorite measured to date. Therefore, V isotopes support models of Earth accretion in which a significant portion of Earth was formed from material that is not present in our meteorite collections.

Mariko Kato¹, Hideyuki Saio², and Izumi Hachisu³
The Astrophysical Journal 863, 125 Link to Article [https://doi.org/10.3847/1538-4357/aad327]
¹Department of Astronomy, Keio University, Hiyoshi, Yokohama 223-8521, Japan
²Astronomical Institute, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan
³Department of Earth Science and Astronomy, College of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan

Type Ia supernovae (SNe Ia) often show high-velocity absorption features (HVFs) in their early phase spectra; however, the origin of the HVFs is unknown. We show that a near-Chandrasekhar-mass white dwarf (WD) develops a silicon-rich layer on a carbon–oxygen (CO) core before it explodes as an SN Ia. We calculated the nuclear yields in successive helium shell flashes for 1.0 M _☉, 1.2 M _☉, and 1.35 M _☉ CO WDs accreting helium-rich matter with several mass-accretion rates, ranging from 1 × 10⁻⁷ M _☉ yr⁻¹ to 7.5 × 10⁻⁷ M _☉ yr⁻¹. For the 1.35 M _☉ WD with the accretion rate of 1.6 × 10⁻⁷ M _☉ yr⁻¹, the surface layer developed as helium burning ash and consisted of 40% ²⁴Mg, 33% ¹²C, 23% ²⁸Si, and a few percent of ²⁰Ne by weight. For a higher mass-accretion rate of 7.5 × 10⁻⁷ M _☉ yr⁻¹, the surface layer consisted of 58% ¹²C, 31% ²⁴Mg, and 0.43% ²⁸Si. For the 1.2 M_☉ WDs, silicon is produced only for lower mass-accretion rates (2% for 1.6 × 10⁻⁷ M _☉ yr⁻¹). No substantial silicon (<0.07%) is produced on the 1.0 M _☉ WD independently of the mass-accretion rate. If the silicon-rich surface layer is the origin of Si ii HVFs, its characteristics are consistent with that of mass-increasing WDs. We also discuss possible Ca production on very massive WDs (1.38 M _☉).

^1,2P. Woitke, ^1,2,5Ch. Helling, ^1,2G. H. Hunter, ^1,2J. D. Millard, ^1,2G. E. Turner, ^1,2M. Worters, ³J. Blecic, ⁴J. W. Stock
Astronomy & Astrophysics 614, A1 Link to Article [https://doi.org/10.1051/0004-6361/201732193]
¹SUPA, School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
²Centre for Exoplanet Science, University of St Andrews, St Andrews, UK
³New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
⁴Department of Chemistry and Environmental Science, Medgar Evers College – City University of New York, 1650 Bedford Avenue, Brooklyn, NY 11235, USA
⁵Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands

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^1,2David Morate, ^1,2Julia de León, ³Mário De Prá, ^1,2Javier Licandro, ^1,4Antonio Cabrera-Lavers, ⁵Humberto Campins, ⁶Noemí Pinilla-Alonso
Astronomy & Astrophysics 610, A25 Link to Article [https://doi.org/10.1051/0004-6361/201731407]
¹Instituto de Astrofísica de Canarias (IAC), C/vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
e-mail: damog@iac.es
²Departamento de Astrofca, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
³Observatório Nacional, Coordenao de Astronomia e Astrofca, 20921-400 Rio de Janeiro, Brazil
⁴GTC Project Office, 38205 La Laguna, Tenerife, Spain
⁵Physics Department, University of Central Florida, PO Box 162385, Orlando, FL 32816-2385, USA
⁵Florida Space Institute, University of Central Florida, Orlando, FL 32816, USA

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¹E. Dartois, ²C. Engrand, ²J. Duprat, ²M. Godard, ²E. Charon, ²L. Delauche, ³C. Sandt, ³F. Borondics
Astronomy & Astrophysics 609, A64 Link to Article [https://doi.org/10.1051/0004-6361/201731322]
¹Institut d’Astrophysique Spatiale (IAS), CNRS, Univ. Paris Sud, Université Paris-Saclay, 91405 Orsay, France
e-mail: emmanuel.dartois@ias.u-psud.fr
²Centre de Sciences Nucléaires et de Sciences de la Matière (CSNSM), CNRS/IN2P3, Univ. Paris Sud, Université Paris-Saclay, 91405 Orsay, France
³Synchrotron SOLEIL, L’Orme des Merisiers, BP48 Saint Aubin, 91192 Gif-sur-Yvette Cedex, France

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¹A.P.Crósta,^2,3W.U.Reimold,⁴M.A.R.Vasconcelos, ²N.Hauser, ¹G.J.G.Oliveira, ¹M.V.Maziviero, ⁵A.M.Góes
Chemie der Erde (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2018.09.002]
¹State University of Campinas, Brazil
²University of Brasília, Brazil
³Natural History Museum—Leibniz Institute for Evolution and Biodiversity Research, Berlin, Germany
⁴Federal University of Bahia, Brazil
⁵University of São Paulo, Brazil
Copyright Elsevier

In the first part of this review of the impact record of South America, we have presented an up-to-date introduction to impact processes and to the criteria to identify/confirm an impact structure and related deposits, as well as a comprehensive examination of Brazilian impact structures. The current paper complements the previous one, by reviewing the impact record of other countries of South America and providing current information on a number of proposed impact structures. Here, we also review those structures that have already been discarded as not being formed by meteorite impact. In addition, current information on impact-related deposits is presented, focusing on impact glasses and tektites known from this continent, as well as on the rare K–Pg boundary occurrences revealed to date and on reports of possible large airbursts. We expect that this article will not only provide systematic and up-to-date information on the subject, but also encourage members of the South American geoscientific community to be aware of the importance of impact cratering and make use of the criteria and tools to identify impact structures and impact deposits, thus potentially contributing to expansion and improvement of the South American impact record.

¹Michael C. Bouchard,¹Bradley L. Jolliff
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005631]
¹Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, Missouri
Published by arrangement with John Wiley & Sons

The Mars rover Opportunity has collected in‐situ compositional data with the Alpha Particle X‐Ray Spectrometer at almost 500 sites. To analyze these data, hierarchical clustering analysis and an error‐weighted similarity index are applied to a subset of 57 APXS target compositions and selected martian meteorites. Hierarchical clustering provides a rapid first approximation of compositional relationships whereas the error‐weighted similarity index provides an in‐depth and quantifiable comparison of individual composition pairs. These analyses are combined into a statistical grouping model that provides insight into lithologic relationships and is critically informed by examination of Panoramic Camera and Microscopic Imager images. Major lithologies are (1) the Burns formation sulfate sandstones, (2) Shoemaker impact breccias (Endeavour crater ejecta/rim deposits), (3) the morphologically distinct Grasberg formation, associated with Endeavour crater rim deposits, (4) the Matijevic formation, an exposure interpreted to be Endeavour crater target rocks, and (5) erratics or other rocks that do not cluster with groups 1‐4. The Grasberg formation is more similar to the Shoemaker formation than any other formation, and thus likely incorporated eroded Shoemaker material. The lowest Shoemaker member (Copper Cliff breccia) may contain material from the pre‐ impact Matijevic formation. The Matijevic formation is the most chemically distinct formation and is most similar to the volcanic erratic rock “Marquette Island.” Clustering and similarity index values also show that regolith breccia martian meteorites (represented by the NWA 7475/7034 paired meteorites) are similar in bulk composition to Mars surface materials at Meridiani, especially the Matijevic formation.

¹C. B. Kiddell, ¹E. A. Cloutis, ¹B. R. Dagdick, ¹J. M. Stromberg, ¹D. M. Applin, ¹J. P. Mann
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005600]
¹Dept. of Geography, University of Winnipeg, Winnipeg, Manitoba, Canada
Published by arrangement with John Wiley & Sons

Carbonaceous chondrite meteorites (CCs) are among the most primitive materials in the solar system and provide important insights into solar system history and evolution. A number of planetary spacecraft missions will visit asteroids that are thought to compositionally resemble these meteorites. To better assist sample acquisition in terms of how the physical properties of CCs affect their reflectance spectra, we investigated the spectral reflectance properties of solid and powdered CCs, and powder coatings on slabs of a number of CCs, including CB, CH, CK, CM, CO, CR, and CV classes. We found that decreasing grain size leads to increasing reflectance across the ~500‐2500 nm range and steeper spectral slope, regardless of CC type. Powdered CC reflectance spectra are brighter beyond ~500 nm and redder than bare roughened slabs. For powders sprinkled on slabs, as the powder coating gets thicker, spectral slopes get redder.

Optically thick fine‐grained powders are brighter beyond ~500 nm and are as red or redder, than slabs covered with airfall dust (for dust thicknesses up to a few hundred microns). Diagnostic absorption features of CC minerals, particularly those in the 1000 nm region attributable to Fe‐bearing silicates, are ubiquitous regardless of physical properties. Reflectance spectra of terrestrially weathered (i.e., “rusty”) CCs are strongly modified below ~700 nm and in the 900 and 1900 nm regions by these Fe oxyhydroxides. Their effects can be mitigated through chemical treatment, but this may also affect pre‐terrestrial ferric iron‐bearing phases. Some spectral characteristics, such as hydrous and anhydrous silicate absorption bands in CC spectra, are present regardless of physical properties (fine‐grained dust, powders, slabs, dust on slabs). Other spectral characteristics (such as albedo and spectral slope) vary as a function of physical properties, indicates that reflectance spectroscopy could be used to ascribe spectral variations across an asteroid’s surface to either physical or compositional causes. This information can, in turn, be used to inform site selection for asteroid sample return missions, where both composition and physical properties are important drivers. When searching for fine‐grained areas on an asteroid to sample, the best indication would be the brightest and reddest‐sloped spectra.