¹D. J. Wilson, ¹B. T. Gänsicke, ²D. Koester, ¹O. Toloza, ¹A. F. Pala, ¹E. Breedt,³S. G. Parsons

¹Department of Physics, University of Warwick, Coventry CV4 7AL, UK
²Institut für Theoretische Physik und Astrophysik, University of Kiel, D-24098 Kiel, Germany
³Departamento de Física y Astronomía, Universidad de Valparaíso, Avenida Gran Bretaña 1111, Valparaíso 2360102, Chile

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Reference
Wilson DJ, Gänsicke BT, Koester D, Toloza O, Pala AF, Breedt E, Parsons SG (2015)
The composition of a disrupted extrasolar planetesimal at SDSS J0845+2257 (Ton 345). Monthly Notices of the Royal Astronomical Society 451, 3237-3248.
Link to Article [doi: 10.1093/mnras/stv1201]

¹Aaron S. Bella, ¹Charles Shearera, ²J. Maarten deMoor, ¹Paula Provencio
¹Institute of Meteoritics and Department of Earth and Planetary Sciences, University of New Mexico
²OVSICORI, Universidad Nacional, Heredia, Costa Rica

In this work, we investigate the compositions and origin of metasomatic fluids responsible for the formation of sulfide replacement textures in Mg-Suite lithologies of lunar samples 67915-149 and 67915-150. We have constructed a quantitative thermodynamic model of the composition of the metasomatic fluid using fO2, fS2, and temperature constraints derived from a thermodynamic analysis of the metasomatic fluid-mineral reactions and the measured compositions of the phases in the sulfide assemblages. Results from this modeling indicate that the metasomatic fluid responsible for the formation of the sulfide replacement textures was likely dominated by a combination of H2 and CH4, with minor abundances of H2O, CO, and H2S. The modeling indicates that H2S was, by orders of magnitude, the dominant S-species present in the metasomatic fluid and S isotopes in the replacement sulfides suggest that the fluid experienced significant removal of H2S by sulfide precipitation. The calculated H2 and H2O contents of the metasomatic fluid are consistent with those that might be expected for the late stage degassing of shallowly emplaced, intrusive magma bodies.

Reference
Bell AS, Charles Shearera, deMoor JM, Provencio P (2015) Using the Sulfide Replacement Petrology in Lunar Breccia 67915 to Construct a Thermodynamic Model of S-bearing Fluid in the Lunar Crust. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.08.002]

Copyright Elsevier

The most popular papers on Cosmochemistry Papers in August were:

1-Holst JC, Paton C, Wielandt D., Bizzarro M. (2015) Tungsten isotopes in bulk meteorites and their inclusions—Implications for processing of presolar components in the solar protoplanetary disk. Meteoritics&Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12488]

2-Groopman E, Zinner E, Amari S, Gyngard F, Hoppe P, Jadhav M, Lin Y, Xu Y, Marhas K, Nittler LR (2015) Inferred Initial 26Al/27Al Ratios in Presolar Stardust Grains from Supernovae are Higher than Previously Estimated. Astrophyical Journal 803, 31. Link to Article [doi:10.1088/0004-637X/809/1/31]

3-Hoppe P, Leitner J, Kodolányi J (2015) New Constraints on the Abundances of Silicate and Oxide Stardust from Supernovae in the Acfer 094 Meteorite. Astrophysical Journal 808 L9. Link to Article [doi:10.1088/2041-8205/808/1/L9]

4-Lantz C, Brunetto R, Barucci MA, Dartois E, Duprat J, Engrand C, Godard M, Ledu D, Quirico E (2015) Ion irradiation of the Murchison meteorite: Visible to mid-infrared spectroscopic results. Astronomy & Astrophysics 577, A41 Link to Article [dx.doi.org/10.1051/0004-6361/201425398 ]

5-Chen H-W, Lee T, Lee D-C, Chen J-C (2015) Correlation of 48Ca, 50Ti, and 138La Heterogeneity in the Allende Refractory Inclusions. Astrophysical Journal 806 L21. Link to Article [doi:10.1088/2041-8205/806/1/L21]

^1,2Tomáš Magna, ¹Nikolaus Gussone, ^1,3Klaus Mezger
¹Institut für Mineralogie, Universität Münster, Corrensstr. 24, D-48149 Münster, Germany
²Czech Geological Survey, Klárov 3, CZ-118 21 Prague, Czech Republic
³Institut für Geologie, Universität Bern, Baltzerstr. 1+3, CH-3012 Bern, Switzerland

New Ca isotope data from a suite of Martian meteorites provide constraints on the Ca isotope composition of the Martian mantle and possible recycling of surface materials back into the mantle. A mean δ44/40Ca of 1.04±0.09‰1.04±0.09‰ (2SD) is estimated for the Martian mantle which can also be taken as an approximation for Bulk Silicate Mars. This value is identical with the estimates for Bulk Silicate Earth, and the inner Solar System planets can therefore be considered homogeneous with respect to Ca isotopes. The Ca isotope composition of two Martian dunites varies by ∼0.3‰∼0.3‰ despite strong chemical and mineralogical similarities and this difference can be caused by the presence of carbonate, probably of pre-terrestrial origin, implying a protracted period of the existence of CaCO3-rich fluids and sufficient amounts of CO2 on the surface of Mars. The variability of δ44/40Ca within the groups of shergottites and nakhlites (clinopyroxene cumulates) cannot be related to partial melting and fractional crystallization in any simple way. However, there is no necessity of incorporating surface lithologies with isotopically light Ca into the mantle sources of Martian meteorites. These inferences are consistent with the absence of large scale crust–mantle recycling and thus of plate tectonics on Mars.

Reference
Magna T, Gussone N, Mezger K (2015) The calcium isotope systematics of Mars. Earth and Planetary Science Letters 430, 86–94
Link to Article [doi:10.1016/j.epsl.2015.08.016]
Copyright Elsevier

¹A. Frigeri et al. (>10)*
¹Istituto Nazionale di Astrofisica (INAF), Istituto di Astrofisica e Planetologia Spaziali (IAPS), Via Fosso del Cavaliere 100, Rome, Italy
We currently do not have a copyright agreement with this publisher and cannot display the abstract here

In this manuscript we present the mineralogic mapping of the Av-9 Numisia quadrangle of Vesta using the most up-to-date data from the NASA–Dawn mission.

This quadrangle is located in Vesta’s equatorial zone (22°° south to 22°° north, 218°° to 288°° east, in Claudia coordinate system) and takes its name from the impact crater Numisia. The main feature, which dominates the quadrangle, is the Vestalia Terra plateau, a topographic high about 10 km above the surrounding areas. To the south, this region fades into the Rheasilvia basin, while to the north it is bounded by the steep scarp of Postumia basin.

The Visible and Infrared mapping spectrometer (VIR) onboard NASA/Dawn provided the main data source for this work, at an unprecedented level of spatial and spectral resolution. In particular we are using spectral parameters to synthesize characteristics of the whole spectra into a single value. Pyroxene-related spectral parameters allow for the detection of lower crust or mantle material (diogenites) and upper crust material (eucrites) in the study area.

The combined analysis of albedo from the Framing Camera, the geologic map and the spectroscopic data offer an interesting opportunity to understand better the surface features of this region of Vesta, and their Evolution. Numisia, Cornelia, Fabia, Teia and Drusilla are the main craters in the study area, rich in bright and dark material outcrops, pitted terrains and OH-rich materials.

Using the spectral parameters we demonstrate that the internal composition of Vestalia Terra is mainly diogenite-rich howardite, as shown by materials excavated by Cornelia and Fabia, and the composition of the slope north of Vestalia Terra. This agrees with the strong positive Bouguer Anomaly observed in the area, indicating a higher density of these features in relation to the surrounding Areas. Besides the recently published works based on gravimetric modelling and geologic interpretation, the mineralogic mapping presented herein gives an additional contribution, in order to depict a more complete geologic history of the Numisia quadrangle of Vesta.

Reference
Frigeri A et al. (2015) Mineralogic Mapping of the Av-9 Numisia quadrangle of Vesta. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.07.029]
Copyright Elsevier

^1,2Laura Flagg,²Alycia J. Weinberger,³Keith Matthews
¹Department of Physics and Astronomy, Northern Arizona University, Flagstaff, AZ 86011-6010, USA
²Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015, USA
³Caltech Optical Observatories, California Institute of Technology, MC 301-17, Pasadena, CA 91125, USA

The detectability of planetesimal impacts on imaged exoplanets can be measured using Jupiter during the 1994 comet Shoemaker-Levy 9 events as a proxy. By integrating the whole planet flux with and without impact spots, the effect of the impacts at wavelengths from 2 – 4 μμm is revealed. Jupiter’s reflected light spectrum in the near-infrared is dominated by its methane opacity including a deep band at 2.3 μμm. After the impact, sunlight that would have normally been absorbed by the large amount of methane in Jupiter’s atmosphere was instead reflected by the cometary material from the impacts. As a result, at 2.3 μμm, where the planet would normally have low reflectivity, it brightened substantially and stayed brighter for at least a month.

Reference
Flagg L, Weinberger AJ, Matthews K (2015) Detectability of Planetesimal Impacts on Giant Exoplanets. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.08.024]
Copyright Elsevier

^1,2Marina A. Ivanova, ¹Cyril A. Lorenz, ³Alexander N. Krot,²Glenn J. MacPherson
¹Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academy of Sciences, Moscow, Russia
²National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia, USA
³Hawaiʻi Institute of Geophysics and Planetology, University of Hawaiʻi at Mānoa, Honolulu, Hawaiʻi, USA

A calcium-aluminum-rich inclusion 3N from the Northwest Africa (NWA) 3118 CV3 carbonaceous chondrite is a unique cm-sized compound object, primarily a forsterite-bearing type B (FoB) CAI, that encloses at least 26 smaller CAIs of different types, including compact type A (CTA), B, C, and an ultra-refractory inclusion. Relative to typical type A and B CAIs found elsewhere, the bulk compositions of the types A and B CAIs within 3N more closely match the bulk compositions predicted by equilibrium condensation of a gas of solar composition. Being trapped within the FoB melt may have protected them from melt evaporation that affected most “stand-alone” CAIs. 3N originated either as an aggregate of many smaller (mostly types A, B, C) CAIs plus accreted Fo-bearing material (like an amoeboid olivine aggregate) which experienced partial melting of the whole, or else as a FoB melt droplet that collided with and trapped many smaller solid CAIs. In the former case, 3N recorded the earliest accretion of pebble-sized bodies known. In the latter case, the presence of a large number of individual refractory inclusions within 3N suggests a very high local density of refractory solids in the immediate region of the host CAI during the brief time while it was melted. Collisions would have occurred on time scales of hours at most, assuming a melt solidification interval for the host CAI of 300–400 °C (maximum) and a cooling rate of ~10 °C/h.

Reference
Ivanov MA, Lorenz CA, Krot AN, MacPherson GJ (2015) A compound Ca-, Al-rich inclusion from CV3 chondrite Northwest Africa 3118: Implications for understanding processes during CAI Formation. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12489]
Published by Arrangement with John Wiley&Sons

¹A. D. Beard, ^1,2H. Downes,³M. Chaussidon
¹Department of Earth and Planetary Sciences, UCL/Birkbeck Centre for Planetary Sciences, Birkbeck, London, UK
²Department of Earth Sciences, Natural History Museum, London, UK
³Institute of Physics of the Globe, Paris, France

EET 87720 is a polymict ureilite breccia known to contain numerous nonindigenous fragments. We have discovered a microgranitic clast in an interior chip of Elephant Moraine (EET) 87720. The clast consists of a granophyre-like intergrowth of a pure SiO2 phase (tridymite) and albite, mantling a zoned oligoclase phenocryst. In the intergrowth, the tridymite occurs as thin elongate vermicular blebs within larger albite crystals. The granophyre-like intergrowth and the oligoclase phenocryst share a common margin, suggesting that the clast was originally part of a larger fragment. An estimate of its bulk composition is equivalent to that of granite (77 wt% SiO2). Patches of high-Si K-bearing glass occur interstitially within the clast; they have high concentrations of SO3 (11–12 wt%) and contain Cl (0.6 wt%), suggesting that the clast formed on a volatile-rich parent body perhaps resembling early Mars. The mean oxygen isotope composition of the feldspar and tridymite in the clast is very different from the oxygen isotope compositions of ureilites, and is similar to those of silicate inclusions in IIE and IVA irons. Thus, the clast is not indigenous to the ureilite parent body, but it provides evidence for the formation of evolved melts on an unknown parent body in the early solar system.

Reference
Beard AD, Downes, H, Chaussidon M (2015) Petrology of a nonindigenous microgranitic clast in polymict ureilite EET 87720: Evidence for formation of evolved melt on an unknown parent Body. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12484]

Published by arrangement with John Wiley&Sons

¹Lydia Bonal et al. (>10)*
¹Institut de Planétologie et d’Astrophysique de Grenoble, CNRS/UJF Grenoble 1, Grenoble, France
*Find the extensive, full author and affiliation list on the publishers website

Hayabusa-returned samples offer a unique perspective for understanding the link between asteroids and cosmomaterials available in the laboratory, and provide insights on the early stages of surface space weathering. This study characterizes the mineralogy and the extent of space weathering of the three Itokawa particles RA-QD02-0163, RA-QD02-0174, and RA-QD02-0213 provided by JAXA to our consortium. We report here a series of results based on nondestructive analyses through visible-near-infrared reflectance and Raman spectroscopy. Results were obtained on the raw particles, both in their original containers and deposited on diamond windows. Identification of the minerals, characterization of their elemental compositions, and measurements of their relative abundances were led through Raman spectroscopy in punctual and automatic mode. Reflectance spectra in the visible and near-IR wavelengths constrain the mineralogy of the grains and allow direct comparison with the surface of Itokawa. The spectra reflect the extent of space weathering experienced by the three particles. Particle RA-QD02-0163 consists of a heterogeneous mixture of minerals: olivine (Fo76) dominates an assemblage with both Ca-rich (En50, Wo50) and Ca-poor (En85) pyroxenes. The elemental compositions of the silicates are consistent with those previously reported for distinct Hayabusa particles. Particles RA-QD-0174 and RA-QD02-0213 are solely composed of olivine, whose chemical composition is similar to that observed in RA-QD02-0163. It has been previously shown that the S-type asteroid 25143 Itokawa is a breccia of poorly equilibrated LL4 and highly equilibrated LL5 and LL6 materials. The three particles studied here can be related to the least metamorphosed lithology (LL4) based on the high forsterite content of the olivine. Neither carbonaceous matter nor hydrated minerals were detected through Raman on the three allocated particles. The NIR-VIS reflectance (incidence = 45°, light collection at e = 0°) spectra of the three particles, in particular the 1 μm band, are consistent with the presence of both olivine and pyroxene detected via Raman. The spectra of particles RA-QD02-0163 and RA-QD02-0213 are also fully compatible with the ground-based observations of asteroid (25143) Itokawa in terms of both spectral features and slope. By contrast, particle RA-QD02-0174 has a similar 1 μm band depth but higher (redder) spectral slope than the surface of Itokawa. This probably reveals a variable extent of space weathering among the regolith particles. RA-QD02-0174 may contain a higher amount of nanophase metallic iron and nanophase FeS. Such phases are products by space weathering induced by solar wind, previously detected on other Itokawa particles

Reference
Bonal L. et al. (2015) Visible-IR and Raman microspectroscopic investigation of three Itokawa particles collected by Hayabusa: Mineralogy and degree of space weathering based on nondestructive analyses. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12496]
Published by arrangement with John Wiley&Sons

¹Catherine M. Corrigan, ^1,2Michael A. Velbel, ³Edward P. Vicenzi
¹Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia, USA
²Department of Geological Sciences, Michigan State University, East Lansing, Michigan, USA
³Museum Conservation Institute, Smithsonian Institution, Suitland, Maryland, USA

Nakhlites, clinopyroxenite meteorites from Mars, share common crystallization and ejection ages, suggesting that they might have been ejected from the same place on Mars by the same ejection event (impact) and are different samples of the same thick volcanic flow unit or shallow sill. Mean modal abundances and abundance ranges of pyroxene, olivine, and mesostasis vary widely among different thin-sections of an individual nakhlite. Lithologic heterogeneity is the main factor contributing to the observed modal-abundance variations measured in thin-sections prepared from different fragments of the same stone. Two groups of nakhlites are distinguished from one another by which major constituent varies the least and the abundance of that constituent. The group consisting of Nakhla, Lafayette, Governador Valadares, and the Yamato nakhlite pairing group is characterized by low modal mesostasis and pyroxene-olivine covariance, whereas the group consisting of the Miller Range nakhlite pairing group and Northwest Africa 5790 is characterized by low modal olivine and pyroxene-mesostasis covariance. These two groups sample the slowest-cooled interior portion and the chilled margin, respectively, of the nakhlite emplacement body as presently understood, and appear to be also related to recently proposed nakhlite groups independently established using compositional rather than petrographic observations. Phenocryst modal abundances vary with inferred depth in the nakhlite igneous body in a manner consistent with solidification of the nakhlite stack from dynamically sorted phenocryst-rich magmatic crystal-liquid mush.

Reference
Corrigan CM, Velbel MA, Vicenzi EP (2015) Modal abundances of pyroxene, olivine, and mesostasis in nakhlites: Heterogeneity, variation, and implications for nakhlite Emplacement. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12492]
Published by arrangement with John Wiley&Sons