¹Yung-Hsin Liu,¹Kuo-Fang Huang, ¹Der-Chuen Leea
Journal of Analytical Atomic Spectrometry 33, 846-855 Link to Article [DOI: 10.1039/C7JA00400A]
¹Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan

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¹Bernard Bourdon, ²Mathieu Roskosz, ³Remco C.Hin
Earth-Science Reviews 181, 61-81 Link to Article [https://doi.org/10.1016/j.earscirev.2018.04.006]
¹Laboratoire de Géologie de Lyon, ENS de Lyon, UCBL and CNRS, 46 Allée d’Italie, Lyon, France
²IMPMC, MNHN, UPMC, UMR CNRS 7590, 61 rue Buffon, 75005 Paris, France
³School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK

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¹María José Martíneza, ²Francisco J. Marcob
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.06.015]
¹Universidad Politécnica de Valencia. Dept. Matemàtica Aplicada. IUMPA. Camino de Vera SN. 46022. Valencia. Spain
²Universitat Jaume I. Dep. Matemàtiques. IMAC. Campus de Riu Sec. 12071 Castellón. Spain
Copyright Elsevier

The distribution of meteors streams throughout a year from the 5th to the 15th century is investigated, based on a new compilation of meteor records in the diverse European Medieval sources. The records of meteor showers and storms in the chronicles of Korea, Japan, China and Arab have also been considered, and compare their appearance dates with those of showers obtained above, as well as with modern observations. We found that the three sets of data are in agreement with each other, the Perseids, Leonids, and Lyrids being best represented.

¹Yuki Hibiya et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article[https://doi.org/10.1016/j.gca.2018.04.031]
¹Department of Earth and Planetary Science, University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-0033, Japan
Copyright Elsevier

Northwest Africa (NWA) 6704 is a unique achondrite characterized by a near-chondritic major element composition with a remarkably intact igneous texture. To investigate the origin of this unique achondrite, we have conducted a combined petrologic, chemical, and 187Re–187Os, O, and Ti isotopic study. The meteorite consists of orthopyroxene megacrysts (En55–57Wo3–4Fs40–42; Fe/Mn = 1.4) up to 1.7 cm in length with finer interstices of olivine (Fa50–53; Fe/Mn = 1.1–2.1), chromite (Cr# ∼ 0.94), awaruite, sulfides, plagioclase (Ab92An5Or3) and merrillite. The results of morphology, lattice orientation analysis, and mineral chemistry indicate that orthopyroxene megacrysts were originally hollow dendrites that most likely crystallized under high super-saturation and super-cooling conditions (1–102 °C/h), whereas the other phases crystallized between branches of the dendrites in the order of awaruite, chromite → olivine → merrillite → plagioclase. In spite of the inferred high super-saturation, the remarkably large size of orthopyroxene can be explained as a result of crystallization from a melt containing a limited number of nuclei that are preserved as orthopyroxene megacryst cores having high Mg# or including vermicular olivine. The Re–Os isotope data for bulk and metal fractions yield an isochron age of 4576 ± 250 Ma, consistent with only limited open system behavior of highly siderophile elements (HSE) since formation. The bulk chemical composition is characterized by broadly chondritic absolute abundances and only weakly fractionated chondrite-normalized patterns for HSE and rare earth elements (REE), together with substantial depletion of highly volatile elements relative to chondrites. The HSE and REE characteristics indicate that the parental melt and its protolith had not undergone significant segregation of metals, sulfides, or silicate minerals. These combined results suggest that a chondritic precursor to NWA 6704 was heated well above its liquidus temperature so that highly volatile elements were lost and the generated melt initially contained few nuclei of relict orthopyroxene, but the melting and subsequent crystallization took place on a timescale too short to allow magmatic differentiation. Such rapid melting and crystallization might occur as a result of impact on an undifferentiated asteroid. The O–Ti isotope systematics (Δ17O = −1.052 ± 0.004, 2 SD; ε50Ti = 2.28 ± 0.23, 2 SD) indicate that the NWA 6704 parent body sampled the same isotopic reservoirs in the solar nebula as the carbonaceous chondrite parent bodies. This is consistent with carbonaceous chondrite-like refractory element abundances and oxygen fugacity (FMQ = −2.6) in NWA 6704. Yet, the Si/Mg ratio of NWA 6704 is remarkably higher than those of carbonaceous chondrites, suggesting significant nebular fractionation of forsterite in its provenance.

¹T. H. Burbine,²P. C. Buchanan,³R. L. Klima,⁴R. P. Binzel
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005561]
¹Department of Astronomy, Mount Holyoke College, South Hadley, MA, USA
²Department of Geology, Kilgore College, Kilgore, TX, USA
³Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
⁴Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
Published by arrangement with John Wiley & Sons

We compare methods for determining the pyroxene mineralogies of V‐type near‐Earth asteroids from their reflectance spectra. We evaluate whether band centers derived from the spectra of synthetic pyroxenes can be used to achieve greater analytical accuracy than is achieved through the use of band centers derived from the spectra of basaltic achondrites (howardites, eucrites, diogenites or HEDs). We conclude that band centers derived from the reflectance spectra of synthetic pyroxenes with known mineralogies do not provide useful diagnostic information to derive equations for determining accurate pyroxene compositions of V‐type asteroids. Band centers from the reflectance spectra of HEDs with known pyroxene mineralogies can be used to derive equations for determining accurate pyroxene compositions of V‐type asteroids. HEDs are physical mixtures of a number of different types of pyroxenes and best simulate the surfaces of V‐type asteroids. Formulas using the Band I center appear best for determining asteroid pyroxene mineralogies for V‐type asteroids due to the current difficulty in doing accurate temperature corrections to the Band II center. Most of thes observed V‐type near‐Earth asteroids have interpreted mineralogies similar to eucrites or howardites. One of the observed near‐Earth asteroids could possibly have a surface mineralogy similar to diogenites.

¹J. T. Wilson,¹D. J. Lawrence,¹P. N. Peplowski,¹J. T. S. Cahill,²V. R. Eke,²R. J. Massey,³L. F. A. Teodoro
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005589]
¹The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
²Institute for Computational Cosmology, Department of Physics, Durham University, Science Laboratories, Durham, UK
³BAER, Planetary Systems Branch, Space Sciences and Astrobiology Division, MS 245‐3, NASA Ames Research CenterMoffett Field, CA, USA
Published by arrangement with John Wiley & Sons

We present improved resolution maps of the Lunar Prospector Neutron Spectrometer thermal, epithermal and fast neutron data and Gamma‐Ray Spectrometer Th‐line fluxes via global application of pixon image reconstruction techniques. With the use of mock data sets, we show that the pixon image reconstruction method compares favorably with other methods that have been used in planetary neutron and gamma‐ray spectroscopy. The improved thermal neutron maps are able to clearly distinguish variations in composition across the lunar surface, including within the lunar basins of Hertzsprung and Schrödinger. The improvement in resolution reveals a correlation between albedo and thermal neutron flux within the basins. The consequent increase in dynamic range confirms that Hertzsprung basin contains one of the most anorthositic parts of the lunar crust, including nearly pure anorthite over a region tens of km in diameter. At Orientale, the reconstructed epithermal neutron data show broad overlap with cpr but there remains a mismatch between measures of regolith maturity that sample the surface and those that probe the near‐subsurface, which is consistent with a complex layering scenario.

¹Justin Filiberto et al. (>10)
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005635]
¹Southern Illinois University, Department of GeologyCarbondale, IL, USA
²School of Environment, Earth and Ecosystem Sciences, Walton Hall, The Open UniversityMilton Keynes, MK, UK
Published by arrangement with John Wiley & Sons

Northwest Africa (NWA) 6963 was found in Guelmim‐Es‐Semara, Morocco, and based on its bulk chemistry and oxygen isotopes, it was classified as a Martian meteorite. On the basis of a preliminary study of the textures and crystal sizes, it was re‐subclassified as a gabbroic shergottite because of the similarity with terrestrial and lunar gabbros. However, the previous work was not a quantitative investigation of NWA 6963; to supplement the original re‐subclassification and enable full comparison between this and other Martian samples, here we investigate the mineralogy, petrology, geochemistry, quantitative textural analyses, and spectral properties of gabbroic shergottite NWA 6963 to constrain its petrogenesis, including the depth of emplacement (i.e., base of a flow versus crustal intrusion).
NWA 6963 is an enriched shergottite with similar mineralogy to the basaltic shergottites, but importantly, does not contain any fine‐grained mesostasis. Consistent with the mineralogy, the reflectance (VNIR and TIR) spectrum of powdered NWA 6963 is similar to other shergottites because they are all dominated by pyroxene, but its reflectance is distinct in terms of albedo and spectral contrast due to its gabbroic texture. NWA 6963 represents a partial cumulate gabbro that is associated with the basaltic shergottites. Therefore, NWA 6963 could represent a hypabyssal intrusive feeder dike system for the basaltic shergottites that erupted on the surface.

¹Mariek E. Schmidt, ^2,3Glynis M. Perrett, ¹Samantha L. Bray, ¹Nicholas J. Bradley, ^1,4Rebekka E. Lee, ⁵Jeff A. Berger, ⁵John L. Campbell, ⁶Cathy Ly, ²Steven W. Squyres, ⁵Dustin Tesselaar
Journal of Geophysical Research, Planets Link to Article [https://doi.org/10.1029/2018JE005553]
¹Department of Earth Sciences, Brock University, St. Catharines, Ontario, Canada
²Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, NY, USA
³Wilfrid Laurier University, Department of Physics and Computer Science, Waterloo, Ontario, Canada
⁴Lafarge Aggregates, Mississauga, Canada
⁵Department of Physics, University of Guelph, Guelph, Ontario, Canada
⁶Cornell University, Ithaca, NY, USA
Published by arrangement with John Wiley & Sons

A thin, patchy layer of airfall dust covers rock surfaces examined by the Mars Science Lab (MSL) rover Curiosity and complicates interpretation of textures in Mars Hand Lens Imager (MAHLI) images and compositions determined by Alpha Particle X‐ray Spectrometer (APXS). Using three image processing methods, we estimate dust coverages for MAHLI images of APXS targets to Sol 1512. Dust coverages of ‘as is’ rock targets range from 6 to 77% (±5 to 10% estimated error). Targets brushed by the Dust Removal Tool (DRT) range to lower coverages than ‘as is’ targets, but quality depends on surface type; brushed mudstones have the narrowest range and lowest coverages (11‐25%), while sandstones vary, ranging to higher coverages (12‐58%). Groups of rocks with similar compositions (APXS classes) can have strong correlations between dust coverage and SO3/Cl (up to r=0.985). Dust can also strongly affect the lightest elements measured (Na to Ca). By comparing paired ‘as is’ and DRT analyses, using the determined dust coverages, and finding a best fit dust thickness (generally ~10 μm), we model relative contributions of the dust and bedrock to extrapolate dust‐free compositions for homogeneous APXS classes. The dust is basaltic with high S and Cl. Dust‐free rocks have higher SiO2 and Na2O (up to 6.5 wt% and 0.5 wt% higher, respectively) and lower SO3 and CaO (up to 5.5 wt% and 1.3 wt% lower, respectively) than dusty equivalents. Dust most influences compositions that are very different from average Mars, including the alkali‐rich, MgO‐poor Jake M class.

^1,2Lu Pan, ^1,3Bethany L. Ehlmann
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2017JE005461]
¹Division of Geological and Planetary Sciences, California Institute of TechnologyPasadena, CA, USA
²Laboratoire de Geologie de Lyon, Université Claude Bernard Lyon 1Villeurbanne, France
³Jet Propulsion Laboratory, California Institute of TechnologyPasadena, CA, USA
Published by Arrangement with John Wiley & Sons

Amazonian‐aged Lyot crater is the best‐preserved and deepest peak‐ring impact crater (diameter, D=220km) in the northern lowlands of Mars. Morphological features including scouring channels emanating from its ejecta and small channels within the crater have been examined previously to understand hydrological activity associated with the crater. In this study, we analyze images acquired by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on board the Mars Reconnaissance Orbiter (MRO) to investigate the mineralogical record in Lyot and its surroundings, which are presently enriched in ground ice, to understand the associated aqueous processes, their relative timing, and a possible role for ground ice in hydrous mineral formation. We find diverse hydrous minerals, including Fe/Mg phyllosilicates, chlorite, illite/muscovite and prehnite in Lyot crater walls, central peak, and ejecta, as well as in two craters to the west of Lyot. The exposure and distribution of the hydrous minerals suggests they are related to the impact process, either exposed by the excavation of hydrothermally altered rocks or formed through syn‐depositional hydrothermal alteration immediately after impacts. The Lyot impact induced channel formation to the north, but no mineralogical evidence of aqueous alteration associated with the channels is observed. The sinuous channels within Lyot, diverted by bedrock units with hydrous mineral detections, did not cause mineralization but likely represent the last stage of water activity in Lyot crater. The separate episodes of water activity indicate flow of liquid water on Mars’ surface during the Amazonian but limited to no aqueous alteration to generate hydrous minerals.

¹Arya Udry,²Esteban Gazel,³Harry Y. McSween Jr
Journal of Geophyisical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005602]
¹Department of Geoscience, University of Nevada, Las Vegas
²Department of Earth and Atmospheric Sciences, Cornell University
³Department of Earth and Planetary Sciences, University of Tennessee
Published by Arrangement with John Wiley & Sons

The recent discovery of some ancient evolved rocks in Gale crater by the Curiosity rover has prompted the hypothesis that continental crust formed in early martian history. Here we present petrological modeling that attempts to explain this lithological diversity by magma fractionation. Using the thermodynamical software MELTS, we model fractional crystallization of different martian starting compositions that might generate felsic igneous compositions like those analyzed at Gale crater using different variables, such as pressure, oxygen fugacities, and water content. We show that similar chemical and mineralogical compositions observed in Gale crater felsic rocks can readily be obtained through different degrees of fractional crystallization of basaltic compositions measured on the martian surface. The results suggest that Gale crater rocks may not represent true primary liquids as they possibly accumulated and/or fractionated feldspar. In terms of major element compositions and mineralogy, we found that the Gale crater felsic compositions are more similar to fractionated magmas produced in Earth’s intraplate volcanoes than to terrestrial felsic continental crust as represented by tonalite‐trondhjemite‐granodiorite (TTG) suites. We conclude that the felsic rocks in Gale crater do not represent continental crust, as it is defined on Earth.