¹P. Vernazza et al. (>10)*
¹Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, F-13388, Marseille, France
*Find the extensive, full author and affiliation list on the publishers website

Meteorites have long been considered as reflections of the compositional diversity of main belt asteroids and consequently they have been used to decipher their origin, formation, and evolution. However, while some meteorites are known to sample the surfaces of metallic, rocky and hydrated asteroids (about one-third of the mass of the belt), the low-density icy asteroids (C-, P-, and D-types), representing the rest of the main belt, appear to be unsampled in our meteorite collections. Here we provide conclusive evidence that the surface compositions of these icy bodies are compatible with those of the most common extraterrestrial materials (by mass), namely anhydrous interplanetary dust particles (IDPs). Given that these particles are quite different from known meteorites, it follows that the composition of the asteroid belt consists largely of more friable material not well represented by the cohesive meteorites in our collections. In the light of our current understanding of the early dynamical evolution of the solar system, meteorites likely sample bodies formed in the inner region of the solar system (0.5–4 AU) whereas chondritic porous IDPs sample bodies that formed in the outer region (>5 AU).

Reference
Vernazza P. et al. (2015) Interplanetary Dust Particles as Samples of Icy Asteroids. Astrophysical Journal 806, 204.
Link to Article [doi:10.1088/0004-637X/806/2/204]

^1,Emmanuel Jacquet, ³Olivier Alard, ¹Matthieu Gounelle
¹Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, CNRS & Muséum National d’Histoire Naturelle, UMR 7202, Paris, France
²Canadian Institute for Theoretical Astrophysics, Toronto, Ontario, Canada
³Géosciences Montpellier, UMR 5243, Université de Montpellier II, Montpellier Cedex 5, France

We report in situ LA-ICP-MS trace element analyses of silicate phases in olivine-bearing chondrules in the Sahara 97096 (EH3) enstatite chondrite. Most olivine and enstatite present rare earth element (REE) patterns comparable to their counterparts in type I chondrules in ordinary chondrites. They thus likely share a similar igneous origin, likely under similar redox conditions. The mesostasis however frequently shows negative Eu and/or Yb (and more rarely Sm) anomalies, evidently out of equilibrium with olivine and enstatite. We suggest that this reflects crystallization of oldhamite during a sulfidation event, already inferred by others, during which the mesostasis was molten, where the complementary positive Eu and Yb anomalies exhibited by oldhamite would have possibly arisen due to a divalent state of these elements. Much of this igneous oldhamite would have been expelled from the chondrules, presumably by inertial acceleration or surface tension effects, and would have contributed to the high abundance of opaque nodules found outside them in EH chondrites. In two chondrules, olivine and enstatite exhibit negatively sloped REE patterns, which may be an extreme manifestation of a general phenomenon (possibly linked to near-liquidus partitioning) underlying the overabundance of light REE observed in most chondrule silicates relative to equilibrium predictions. The silicate phases in one of these two chondrules show complementary Eu, Yb, and Sm anomalies providing direct evidence for the postulated occurrence of the divalent state for these elements at some stage in the formation reservoir of enstatite chondrites. Our work supports the idea that the peculiarities of enstatite chondrites may not require a condensation sequence at high C/O ratios as has long been believed.

Reference
Jacquet E, Alard O, Gounelle M (2015) The formation conditions of enstatite chondrites: Insights from trace element geochemistry of olivine-bearing chondrules in Sahara 97096 (EH3). Meteoritics&Planetary Science (in Press). Link to Article [DOI: 10.1111/maps.12481]
Published by arrangement with John Wiley&Sons

¹Priscille Cuvillier, ¹Hugues Leroux, ¹Damien Jacob andPierre Hirel
¹Unité Matériaux et Transformations UMR 8207, Université Lille 1 and CNRS, Villeneuve d’Ascq, France

The Allende matrix is dominated by micron-sized lath-shaped fayalitic olivine grains with a narrow compositional range (Fa40–50). Fayalitic olivines also occur as rims around forsterite grains in chondrules and isolated forsterite fragments in the matrix or as veins cross-cutting the grains. Allende is a type 3 CV carbonaceous chondrite having experienced a moderate thermal metamorphism. There is therefore a strong chemical disequilibrium between the large forsterite grains and the fayalite-rich fine-grained matrix. Chemical gradients at interfaces are poorly developed and thus not accessible using conventional techniques. Here, we used analytical transmission electron microscopy to study the microstructure of the fayalite-rich matrix grains and interfaces with forsterite fragments. We confirm that fayalitic grains in the matrix and fayalitic rims around forsterite fragments have the same properties, suggesting a common origin after the accretion of the parent body of Allende. Composition profiles at the rim/forsterite interfaces exhibit a plateau in the rim (typically Fa45), a compositional jump of 10 Fa% at the interface, and a concentration gradient in the forsterite grain. Whatever the studied forsterite grain or whatever the nature of the interface, the Fe-Mg profiles in forsterite grains have the same length of about 1.5 μm. This strongly suggests that the composition profiles were formed by solid-state diffusion during the thermal metamorphism episode. Time–temperature couples associated with the diffusion process during thermal metamorphism are deduced from profile modeling. Considering the uncertainties on the diffusion coefficient value, we found that the peak temperature in Allende is ranging from 425 to 505 °C.

Reference
Cuvillier P, Leroux H, Jacob D, Hirel P (2015) Fe-Mg interdiffusion profiles in rimmed forsterite grains in the Allende matrix: Time–temperature constraints for the parent body metamorphism. Meteoritics&Planetary Science (in Press)
Link to Article: [DOI: 10.1111/maps.12493]
Published by arrangement with John wiley & Sons

¹J. C. Holst, ¹C. Paton, ¹D. Wielandt, ¹M. Bizzarro
¹Centre for Star and Planet Formation and Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark

We present high precision, low- and high-resolution tungsten isotope measurements of iron meteorites Cape York (IIIAB), Rhine Villa (IIIE), Bendego (IC), and the IVB iron meteorites Tlacotepec, Skookum, and Weaver Mountains, as well as CI chondrite Ivuna, a CV3 chondrite refractory inclusion (CAI BE), and terrestrial standards. Our high precision tungsten isotope data show that the distribution of the rare p-process nuclide 180W is homogeneous among chondrites, iron meteorites, and the refractory inclusion. One exception to this pattern is the IVB iron meteorite group, which displays variable excesses relative to the terrestrial standard, possibly related to decay of rare 184Os. Such anomalies are not the result of analytical artifacts and cannot be caused by sampling of a protoplanetary disk characterized by p-process isotope heterogeneity. In contrast, we find that 183W is variable due to a nucleosynthetic s-process deficit/r-process excess among chondrites and iron meteorites. This variability supports the widespread nucleosynthetic s/r-process heterogeneity in the protoplanetary disk inferred from other isotope systems and we show that W and Ni isotope variability is correlated. Correlated isotope heterogeneity for elements of distinct nucleosynthetic origin (183W and 58Ni) is best explained by thermal processing in the protoplanetary disk during which thermally labile carrier phases are unmixed by vaporization thereby imparting isotope anomalies on the residual processed reservoir.

Reference
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]
Published by arrangement with John Wiley&Sons

¹Dustin Trail, ²Nicholas D. Tailby, ²Maggie Sochko, ¹Michael R. Ackerson
¹Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York.
²Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, New York.

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Reference
Trail D, Tailby ND, Sochko M, Ackerson MR (2015) Possible Biosphere-Lithosphere Interactions Preserved in Igneous Zircon and Implications for Hadean Earth. Astrobiology 15, 575-586.
Link to Article [doi:10.1089/ast.2014.1248]

The most popular papers on Cosmochemistry Papers in July were:

1-Howarth GH, Pernet-Fisher JF, Bodnar RJ, Taylor LA (2015) Evidence for the exsolution of Cl-rich fluids in martian magmas: Apatite petrogenesis in the enriched lherzolitic shergottite Northwest Africa 7755. Geochimica et Cosmochimica (in Press) Link to Article [doi:10.1016/j.gca.2015.06.031]

2-Poitrasson F, Zambardi T (2015) An Earth-Moon silicon isotope model to track silicic magma origins. Geochimica et Cosmochimica Acta (in Press) Link to Article [doi:10.1016/j.gca.2015.07.005]

3-Sautter V et al. (2015) In situ evidence for continental crust on early Mars. Nature Geoscience (in Press) Link to Article [doi:10.1038/ngeo2474]

4-Varela ME, Sylvester P, Brandstätter F, Engler A (2015) Nonporphyritic chondrules and chondrule fragments in enstatite chondrites: Insights into their origin and secondary processing. Meteoritics&Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12468]

5-Rubin AE (2015) An American on Paris: Extent of aqueous alteration of a CM chondrite and the petrography of ist refractory and amoeboid olivine inclusions. Meteoritics&Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12482]

¹I. P. Wright, ¹S. Sheridan, ¹S. J. Barber, ¹G. H. Morgan, ¹D. J. Andrews, ¹A. D. Morse
¹Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK.

The surface and subsurface of comets preserve material from the formation of the solar system. The properties of cometary material thus provide insight into the physical and chemical conditions during their formation. We present mass spectra taken by the Ptolemy instrument 20 minutes after the initial touchdown of the Philae lander on the surface of comet 67P/Churyumov-Gerasimenko. Regular mass distributions indicate the presence of a sequence of compounds with additional -CH2- and -O- groups (mass/charge ratios 14 and 16, respectively). Similarities with the detected coma species of comet Halley suggest the presence of a radiation-induced polymer at the surface. Ptolemy measurements also indicate an apparent absence of aromatic compounds such as benzene, a lack of sulfur-bearing species, and very low concentrations of nitrogenous material.

Reference
Wright IP, Sheridan S, Barber SJ, Morgan GH, Andrews DJ, Morse AD (2015) CHO-bearing organic compounds at the surface of 67P/Churyumov-Gerasimenko revealed by Ptolemy. Science 349, 6247
Link to Article [DOI: 10.1126/science.aab0673]
Reprinted with permission from AAAS

¹Tatsuaki Okada, ²Michael E Zolensky, ³Trevor Ireland, ¹Toru Yada
¹Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara 252-5210, Japan
²Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston 77058, TX, USA
³Research School of Earth Sciences, The Australian National University, Canberra ACT 0200, Australia

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

Reference
Okada T, Zolensky ME, Ireland T, Yada T (2015) Science of solar system materials examined from Hayabusa and future missions. Earth, Planets and Space 67:116
Link to Article [doi:10.1186/s40623-015-0235-x]

¹Jennifer Hanley, ²Vincent F. Chevrier, ³R. Scott Barrows, ⁴Chase Swaffer, ²Travis S. Altheide
¹Department of Space Studies, Southwest Research Institute, Boulder, Colorado, USA
²Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, Arkansas, USA
³Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, Colorado, USA

The presence and distribution of oxychlorine salts (e.g. chlorates and perchlorates) on Mars has implications for the stability of water, most notably that they lower the freezing temperature. To date, elemental chlorine has been measured by all lander missions, with the perchlorate ion identified at both the Phoenix and Curiosity landing sites, but detection by near-infrared (NIR) and mid-infrared (MIR) remote sensing has been limited to deposits of anhydrous chlorides. Given that oxychlorine salts can form numerous hydrated phases, we have measured their NIR and MIR reflectance spectra from 1–25 µm for comparison to data collected from orbiting spectrometers. Anhydrous oxychlorine salts show almost no features in the NIR, except for small bands of residual adsorbed water. However, hydrated oxychlorine salts show numerous features due to water in the NIR, specifically at ~1.4 and ~1.9 µm. Increasing the hydration state increases the depth and width of the water bands. All oxychlorine salts exhibit an additional feature at ~2.2 µm due to a Cl-O combination or overtone feature, though it is less prominent in the hydrated perchlorate salts, likely overwhelmed by the ClO4-H2O feature at 2.14 µm. All oxychlorine salts show features in the MIR, due to the fundamental vibrations of Cl-O longward of ~8 µm. The NIR spectral features of hydrated oxychlorine salts are similar to other hydrated salts, especially hydrated sulfates, thus identification from orbit may be ambiguous; however, by utilizing the NIR and MIR laboratory data presented here for comparison, oxychlorine salts may be detectable by orbiting spectrometers.

Reference
Hanley J, Chevrier VF, Barrows RS, Swaffer C, Altheide TS (2015) Near- and mid-infrared reflectance spectra of hydrated oxychlorine salts with implications for Mars. Journal of Geophysical Research (Planets) (in Press)
Link to Article [DOI: 10.1002/2013JE004575]
Published by arrangement with John Wiley & Sons

¹Mario Fischer-Gödde, ^1,2Christoph Burkhardt, ¹Thomas S. Kruijer, ¹Thorsten Kleine
¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
²Origins Laboratory, Department of Geophysical Sciences, The University of Chicago, IL 60637, USA

Nucleosynthetic isotope anomalies in bulk chondrites and differentiated meteorites reflect variable proportions of isotopically diverse presolar components in bulk planetary bodies, but the origin of these heterogeneities is not well understood. Here, the Ru isotope composition of a comprehensive suite of iron meteorites and bulk samples of ordinary, enstatite and carbonaceous chondrites, as well as acid leachates and an insoluble residue of the Allende chondrite are examined using newly developed multi-collector inductively coupled plasma mass spectrometry techniques. Except for IAB iron meteorites and enstatite chondrites, all investigated meteorites show well-resolved Ru isotope anomalies. Of these, within-group Ru isotopic variations observed for samples from a given chemical group of iron meteorites reflect secondary neutron capture induced during prolonged cosmic ray-exposure. After correction of these cosmogenic effects using Pt isotopes as a neutron-dose monitor, the remaining Ru isotope anomalies are nucleosynthetic in nature and are consistent with a deficit in s-process Ru in iron meteorite parent bodies. Similarly, Ru isotope anomalies in bulk ordinary and carbonaceous chondrites also reflect a deficiency in s-process Ru. The sequential dissolution of Allende reveals the presence of an HF-soluble s-process carrier, which is either an unidentified presolar phase or a component that incorporated s-process Ru liberated from SiC grains during nebular or parent body processes. We show that varying proportions of the s-process carrier identified in Allende resulted in the correlated Ru isotope anomalies observed for bulk meteorites, and that all meteorites (except possibly IAB irons and enstatite chondrites) are depleted in this s-process component relative to Ru from the Earth’s mantle. Bulk meteorites exhibit correlated Ru and Mo isotope anomalies, reflecting variable deficits of a common s-process component, but some iron meteorites and carbonaceous chondrites appear to deviate from this correlation. This may reflect unaccounted cosmic effects on Mo isotopes in iron meteorites, sample heterogeneities in carbonaceous chondrites or nebular and parent body processes acting differently on presolar Mo and Ru components.
The identification of s-deficits in Ru isotopes in almost all iron meteorites and chondrites investigated so far implies that meteorites do not seem to represent the material delivered to the Earth’s mantle as a late veneer after cessation of core formation. However, additional analyses of a more comprehensive set of chondrites are necessary to firmly arrive at this conclusion.

Reference
Fischer-Gödde M, Burkhardt C, Kruijer TS, Kleine T (2015) Ru isotope heterogeneity in the solar protoplanetary disk. Geochimica et Cosmochimica Act (in Press)
Link to Article [doi:10.1016/j.gca.2015.07.032]
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