Laura Schaefer¹ and Bruce Fegley Jr.^2,3
Astrophysical Journal 843, 120 Link to Article [https://doi.org/10.3847/1538-4357/aa784f]
¹Arizona State University, School of Earth and Space Exploration, Tempe, AZ 85287, USA
²Planetary Chemistry Laboratory, Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, USA
³McDonnell Center for the Space Sciences, USA

The Earth and other rocky planets and planetesimals in the solar system formed through the mixing of materials from various radial locations in the solar nebula. This primordial material likely had a range of oxidation states as well as bulk compositions and volatile abundances. We investigate the oxygen fugacity produced by the outgassing of mixtures of solid meteoritic material, which approximate the primitive nebular materials. We find that the gas composition and oxygen fugacity of binary and ternary mixtures of meteoritic materials vary depending on the proportion of reduced versus oxidized material, and also find that mixtures using differentiated materials do not show the same oxygen fugacity trends as those using similarly reduced but undifferentiated materials. We also find that simply mixing the gases produced by individual meteoritic materials together does not correctly reproduce the gas composition or oxygen fugacity of the binary and ternary mixtures. We provide tabulated fits for the oxygen fugacities of all of the individual materials and binary mixtures that we investigate. These values may be useful in planetary formation models, models of volatile transport on planetesimals or meteorite parent bodies, or models of trace element partitioning during metal-silicate fractionation.

G. A. Doschek and H. P. Warren
Astrophysical Journal 844, 52 Link to Article [https://doi.org/10.3847/1538-4357/aa7bea]
Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA

Element abundances in the solar photosphere, chromosphere, transition region, and corona are key parameters for investigating sources of the solar wind and for estimating radiative losses in the quiet corona and in dynamical events such as solar flares. Abundances in the solar corona and photosphere differ from each other depending on the first ionization potential (FIP) of the element. Normally, abundances with FIP values less than about 10 eV are about 3–4 times more abundant in the corona than in the photosphere. However, recently, an inverse FIP effect was found in small regions near sunspots where elements with FIP less than 10 eV are less abundant relative to high FIP elements (eV) than they are in the photosphere. This is similar to fully convective stars with large starspots. The inverse FIP effect is predicted to occur in the vicinity of sunspots/starspots. Up to now, the solar anomalous abundances have only been found in very spatially small areas. In this paper, we show that in the vicinity of sunspots there can be substantially larger areas with abundances that are between coronal and photospheric abundances and sometimes just photospheric abundances. In some cases, the FIP effect tends to shut down near sunspots. We examine several active regions with relatively large sunspots that were observed with the Extreme-ultraviolet Imaging Spectrometer on the Hinodespacecraft in cycle 24.

^1,2Khiri, F., ¹Ibhi, A., ³Saint-Gerant, T., ³Medjkane, M., ¹Ouknine, L.
Journal of African Earth Sciences 134, 644-657 Link to Article [DOI: 10.1016/j.jafrearsci.2017.07.022 ]
¹Geoheritage and Geomaterials Laboratory, University Ibn Zohr, Agadir, Morocco
²Regional Center of Trades of Education and Training, Inzegane, Agadir, Morocco
³Identité et différenciation des espaces, de l’environnement et des sociétés (IDEES), Université de Caen, France

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹George J. Flynn, ²Guy J. Consolmagno, ³Peter Brown, ²Robert J. Macke
Chemie der Erde (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2017.04.002]
¹Department of Physics, SUNY-Plattsburgh,101 Broad St., Plattsburgh, NY 12901, USA
²Vatican Observatory, V-00120, Vatican City State
³Department of Physics and Astronomy and Centre for Planetary Science and Exploration, University of Western Ontario, London, N6A 3K7, ON, Canada
Copyright Elsevier

The physical properties of the stone meteorites provide important clues to understanding the formation and physical evolution of material in the Solar protoplanetary disk as well providing indications of the properties of their asteroidal parent bodies. Knowledge of these properties is essential for modeling a number of Solar System processes, such as bolides in planetary atmospheres, the thermal inertia of atmosphereless solid body surfaces, and the internal physical and thermal evolution of asteroids and rock-rich icy bodies. In addition, insight into the physical properties of the asteroids is important for the design of robotic and crewed reconnaissance, lander, and sample return spacecraft missions to the asteroids. One key property is meteorite porosity, which ranges from 0% to more than 40%, similar to the range of porosities seen in asteroids. Porosity affects many of the other physical properties including thermal conductivity, speed of sound, deformation under stress, strength, and response to impact. As a result of the porosity, the properties of most stone meteorites differ significantly from those of compact terrestrial rocks, whose physical properties have been used in many models of asteroid behavior. A few physical properties, such as grain density, magnetic susceptibility, and heat capacity are not functions of porosity. Taken together, the grain density and the magnetic susceptibility can be used to classify unweathered or minimally weathered ordinary chondrites. This provides a rapid screening technique to identify heterogeneous samples, classify new samples, and identify misclassified meteorites or interlopers in strewn fields.

¹Peter H. Edwards et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12953]
¹Department of Physics and Astronomy, Leicester Institute for Space and Earth Observation, University of Leicester, Leicester, UK
Published by arrangement with John Wiley & Sons

The ChemCam instrument on the Mars Science Laboratory (MSL) rover, Curiosity, observed numerous igneous float rocks and conglomerate clasts, reported previously. A new statistical analysis of single-laser-shot spectra of igneous targets observed by ChemCam shows a strong peak at ~55 wt% SiO2 and 6 wt% total alkalis, with a minor secondary maximum at 47–51 wt% SiO2 and lower alkali content. The centers of these distributions, together with the rock textures, indicate that many of the ChemCam igneous targets are trachybasalts, Mg# = 27 but with a secondary concentration of basaltic material, with a focus of compositions around Mg# = 54. We suggest that all of these igneous rocks resulted from low-pressure, olivine-dominated fractionation of Adirondack (MER) class-type basalt compositions. This magmatism has subalkaline, tholeiitic affinities. The similarity of the basalt endmember to much of the Gale sediment compositions in the first 1000 sols of the MSL mission suggests that this type of Fe-rich, relatively low-Mg#, olivine tholeiite is the dominant constituent of the Gale catchment that is the source material for the fine-grained sediments in Gale. The similarity to many Gusev igneous compositions suggests that it is a major constituent of ancient Martian magmas, and distinct from the shergottite parental melts thought to be associated with Tharsis and the Northern Lowlands. The Gale Crater catchment sampled a mixture of this tholeiitic basalt along with alkaline igneous material, together giving some analogies to terrestrial intraplate magmatic provinces.

¹Laura M. Corley et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.09.012]
¹Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, HI, USA
Copyright Elsevier

High-resolution hyperspectral data from Chandrayaan-1’s Moon Mineralogy Mapper (M3) allow detection of olivine on the lunar surface. Olivine exposed at the surface may originate as mantle material or igneous products (intrusive or extrusive). Potential transport mechanisms include excavation of the mantle or lower crustal material by impacts that form basins and complex craters, differentiation of impact melt sheets, or magmatic emplacement of lavas, cumulates or xenoliths. A sample of the lunar mantle, which has not been conclusively identified in the lunar sample collection, would yield fundamental new insights into the composition, structure, and evolution of the lunar interior. Olivine identified in remote spectral data is generally accepted to originate from the primary mantle, because abundant olivine is expected to exist in the mantle and lower crust, yet have sparse occurrences in the upper crust. In this study, we identified 111 M3 single-pixel spectra with characteristic absorption features consistent with olivine at Crisium, Nectaris, and Humorum basins and near the crater Roche. In an effort to determine the origins and transport mechanisms that led to these individual exposures, we estimated mineral abundances using radiative transfer modeling and examined crustal thickness estimates, topography and slope maps, and images from the Lunar Reconnaissance Orbiter Camera (LROC). At Crisium basin, where crustal thickness is near 0 km (Wieczorek et al., 2013), mantle olivine may have been exposed by basin-forming impact and deposited on the rim. Picard crater, which is superposed on the floor of Crisium, also exhibits potential mantle olivine in its ejecta. Within Nectaris basin, olivine exposures are confined to the rims of small craters on the mare, which are inferred to excavate a layer of olivine-rich mare basalt. Olivine occurrences on the rim of Humorum basin, including those located on a graben, are likely to be cumulates of a shallow intrusion that were transported magmatically to the surface. Near Roche crater, olivine may have originated in shallow intrusions (dikes) that reached the subsurface and were exposed by impacts. In addition to verifying both known and previously unidentified olivine exposures, our combined geophysical, spectral, and radiative transfer modeling investigation has allowed identification of both igneous and mantle-derived olivine.

¹Alexey A. Berezhnoy,
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.08.034]
¹Sternberg Astronomical Institute, Moscow State University, Universitetskij pr., 13, 119234 Moscow, Russia
Copyright Elsevier

Based on the equilibrium thermochemical approach and quenching theory, formation of molecules and dust grains in impact-produced clouds formed after collisions between meteoroids and Mercury is considered. Based on observations of Al, Fe, and Mn atoms in the exosphere of Mercury and new results of studies of the elemental composition of the surface of Mercury, quenching temperatures and pressures of main chemical reactions and condensation of dust particles were estimated. The behavior of the main Na-, K-, Ca-, Fe-, Al-, Mn-, Mg-, Si-, Ti, Ni-, Cr-, Co, Zn-, O-, H-, S-, C-, Cl-, N-, and P-containing species delivered to the Hermean exosphere during meteoroid impacts was studied. The importance of meteoroid bombardment as a source of Na, K, Ca, Fe, Al, Mn, Mg, and O atoms in the exosphere of Mercury is discussed.

¹Paul G. Lucey, ¹David Trang, ²Jeffrey R. Johnson, ³Timothy D. Glotch
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.09.010]
¹University of Hawai‘i at Mānoa, Hawai‘i Institute of Geophysics and Planetology, Honolulu, HI, 96822
²Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723
³Department of Geological Sciences, Stony Brook University, Stony Brook, NY 11794
Copyright Elsevier

Several studies have detected the presence of nanophase ferric oxide, such as nanophase hematite, across the martian surface through spacecraft and rover data. In this study, we used the radiative transfer method to detect and quantify the abundance of these nanophase particles. Because the visible/near-infrared spectral characteristics of hematite >10 nm in size are different from nanophase hematite <10 nm, there are not any sufficient optical constants of nanophase hematite to study visible to near-infrared rover/spacecraft data of the martian surface. Consequently, we found that radiative transfer models based upon the optical constants of crystalline hematite are unable to reproduce laboratory spectra of nanophase hematite. In order to match the model spectra to the laboratory spectra, we developed a new set of optical constants of nanophase hematite in the visible and near-infrared and found that radiative transfer models based upon these optical constants consistently model the laboratory spectra. We applied our model to the passive bidirectional reflectance spectra data from the Chemistry and Camera (ChemCam) instrument onboard the Mars Science Laboratory rover, Curiosity. After modeling six spectra representing different major units identified during the first year of rover operations, we found that the nanophase hematite abundance was no more than 4 wt%.

¹Hamed Pourkhorsandi, ¹Jérôme Gattacceca, ¹Bertrand Devouard, ^bMassimo D’Orazio, ¹Pierre Rochette, ³Pierre Beck, ¹Corinne Sonzogni, ^4,5Millarca Valenzuela
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.09.013]
¹CNRS, Aix-Marseille Univ., IRD, Coll. France, CEREGE, Aix-en-Provence, France
²Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy
³Institut de Planétologie et d’Astrophysique de Grenoble, Grenoble, France
⁴Millennium Institute of Astrophysics (MAS), Pontificia Universidad Católica de Chile, Santiago, Chile
⁵Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Santiago, Chile
Copyright Elsevier

El Médano 301 (EM 301) is an ungrouped chondrite with overall texture and trace-element distribution similar to those of ordinary chondrites (OCs), but with silicate (olivine and low-Ca pyroxene) compositions that are more reduced than those in OCs, with average olivine and low-Ca pyroxene of Fa_3.9±0.3 and Fs_12.8±4.9, respectively. These values are far lower than the values for OCs and even for chondrites designed as “reduced” chondrites. Low-Ca pyroxene is the dominant mineral phase and shows zoning with higher MgO contents along the crystal rims and cracks (reverse zoning). The Co content of kamacite is also much lower than the concentrations observed in OCs (below detection limit of 0.18 wt% versus 0.44-37 wt%). Oxygen isotopic composition is Δ¹⁷O = +0.79, +0.78‰ and slightly different from that of OCs. The lower modal olivine/pyroxene ratio, different Infrared (IR) spectra, lower Co content of kamacite, lower mean FeO contents of olivine and pyroxene, different kamacite texture, and different oxygen-isotopic composition show that EM 301 does not belong to a known OC group. EM 301 shows similarities with chondritic clasts in Cumberland Falls aubrite, and with Northwest Africa 7135 (NWA 7135) and Acfer 370 ungrouped chondrites. However, dissimilar to NWA 7135 and the clasts, it does not contain highly reduced mineral phases like daubréelite.

Our observations suggest the formation of EM 301 in a nebular region compositionally similar to OCs but with a different redox state, with oxygen fugacity (ƒO₂) in this region lower than that of OCs and higher than that of enstatite chondrites condensation region. A second, possibly nebular, phase of reduction by the production of reducing gas phases (e.g., C-rich) could be responsible for the subsequent reduction of the primary material and the occurrence of reverse zoning in the low-Ca pyroxene and lower average Fa/Fs ratio. Based on the IR spectra of EM 301 we suggest the possibility that the parent body of this chondrite was a V-type asteroid.

^1,2Matthew J. Genge, ¹Bridie Davies, ^1,2Martin D. Suttle, ³Matthias van Ginneken, ⁴Andrew G. Tomkins
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.09.004]
¹Department of Earth Science and Engineering, Imperial College London, Exhibition Road, London SW7 11BW, UK
²Earth Sciences Department, The Natural History Museum, Cromwell Road, London SW7 2BW, UK
³Earth System Science, Vrije Universiteit Brussel, Pleinlaan, 2 B-1050 Brussel, Belgium
⁴School of Earth, Atmosphere & Environment, Monash University, Melbourne, Victoria 3800, Australia
Copyright Elsevier

I-type cosmic spherules are micrometeorites that formed by melting during atmospheric entry and consist mainly of iron oxides and FeNi metal. I-types are important because they can readily be recovered from sedimentary rocks allowing study of solar system events over geological time. We report the results of a study of the mineralogy and petrology of 88 I-type cosmic spherules recovered from Antarctica in order to evaluate how they formed and evolved during atmospheric entry, to constrain the nature of their precursors and to establish rigorous criteria by which they may be conclusively identified within sediments and sedimentary rocks. Two textural types of I-type cosmic spherule are recognised: (1) metal bead-bearing (MET) spherules dominated by Ni-poor (<1.5 w%) wüstite and FeNi metal (10-95 wt% Ni) with minor magnetite, and (2) metal bead-free (OX) spherules dominated by Ni-rich wüstite (0.5-22.5 wt%) and magnetite. Two varieties of OX spherule are distinguished, magnetite-poor dendritic spherules and magnetite-rich coarse spherules. Six OXMET particles having features of both MET and OX spherules were also observed. The wüstite to magnetite ratios and metal contents of the studied particles testify to their formation by melting of extraterrestrial FeNi grains during progressive oxidation in the atmosphere. Precursors are suggested to be mainly kamacite and rare taenite grains. Vesicle formation within metal beads and extrusion of metallic liquid into surrounding wüstite grain boundaries suggests an evaporated iron sulphide or carbide component within at least 23% of particles. The Ni/Co ratios of metal vary from 14 to >100 and suggest that metal from H-group ordinary, CM, CR and iron meteorites may form the majority of particles. Oxidation during entry heating increases in the series MET<magnetite-poor OX<magnetite-rich OX spherules owing to differences in particle size, entry angle and velocity. Magnetite-poor OX spherules are shown to form by crystallisation of non-stoichiometric wüstite at the liquidus followed by sub-solidus decomposition to magnetite, whilst in magnetite-rich OX spherules magnetite crystallises directly at the liquidus. Magnetite rims found on most particles are suggested to form by oxidation during sub-solidus flight. The separation of metal beads due to deceleration is proposed to have been minor with most OX spherules shown to have been in equilibrium with metal beads containing >80 wt% Ni comprising a particle mass fraction of <0.2. Non-equilibrium effects in the exchange of Ni between wüstite and metal, and magnetite and wüstite are suggested as proxies for the rate of oxidation and cooling rate respectively. Variations in magnetite and wüstite crystal sizes are also suggested to relate to cooling rate allowing relative entry angle of particles to be evaluated. The formation of secondary metal in the form of sub-micron Ni-rich or Pt-group nuggets and as symplectite with magnetite was also identified and suggested to occur largely due to the exsolution of metallic alloys during decomposition of non-stoichiometric wüstite. Weathering is restricted to replacement of metal by iron hydroxides. The following criteria are recommended for the conclusive identification of I-type spherules within sediments and sedimentary rocks: (i) spherical particle morphologies, (ii) dendritic crystal morphologies, (iii) the presence of wüstite and magnetite, (iv) Ni-bearing wüstite and magnetite, and (v) the presence of relict FeNi metal.