¹A. Frigeri, ¹M.C. De Sanctis, ⁵E. Ammannito, ¹F. Tosi, ¹F. Zambon, ³T. McCord, ³J.P. Combe, ²R. Jaumann, ⁴C.A. Raymond, ⁵C.T. Russell
¹Istituto Nazionale di Astrofisica (INAF), Istituto di Astrofisica e Planetologia Spaziali (IAPS), Via Fosso del Cavaliere 100, Rome, Italy
²German Aerospace Center. Institute of Planetary Research, Berlin, Germany
³Bear Fight Institute, Winthrop, WA, USA
⁴Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
⁵Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA, USA

Here we present the spectral parameter maps used in this Surface Composition of Vesta Special Issue. The use of spectral parameters have been important since the first ground-based observations of Vesta as they can describe single mineralogic aspects as abundances or change in surface composition. Mapping these parameters over the surface shows the mineralogic diversity across the asteroid Vesta. In this work we discuss the development of the maps, which are produced from the data of the Visible and Infrared mapping spectrometer onboard NASA’s Dawn mission. We describe how we processed the VIR spectra and how we produced the geometries of data acquisition. Spectra and geometries are used to design a Geographic Information System procedure to mosaic these data. We conclude the article with a description of the trends of the pyroxene-related spectral parameters across the asteroid, and some statistics on the spectral parameters of each map within the quadrangle-based scheme used in this special issue.

Reference
Frigeri A, De Sanctis MC, Ammannito E, Tosi F, Zambon F, McCord T, Combe JP, Jaumann R, Raymond CA, Russell CT (2015) The spectral parameter maps of Vesta from VIR data. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.06.027]
Copyright Elsevier

¹Evan Groopman, ¹Ernst Zinner, ¹Sachiko Amari, ¹Frank Gyngard, ²Peter Hoppe, ³Manavi Jadhav, ⁴Yangting Lin, ⁴Yuchen Xu, ⁵Kuljeet Marhas, ⁶Larry R. Nittler
¹Laboratory for Space Sciences, Physics Department, Washington University, One Brookings Drive, Campus Box 1105, Saint Louis, MO 63130, USA
²Max Planck Institute for Chemistry, Particle Chemistry Department, P.O. Box 3060, D-55020 Mainz, Germany
³Department of the Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA
⁴Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
⁵Planetary Sciences Division, Physical Research Laboratory, Ahmedabad, Gujarat, 380009 India
⁶Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015, USA

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

Reference
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]

^1,2Alyssa K. Cobb, ^1,2Ralph E. Pudritz, ^1,2Ben K. D. Pearce
¹Origins Institute, McMaster University, ABB 241, 1280 Main Street, Hamilton, ON L8S 4M1, Canada
²Department of Physics and Astronomy, McMaster University, ABB 241, 1280 Main Street, Hamilton, ON L8S 4M1, Canada

Carbonaceous chondrite meteorites are known for having high water and organic material contents, including amino acids. Here we address the origin of amino acids in the warm interiors of their parent bodies (planetesimals) within a few million years of their formation, and we connect this with the astrochemistry of their natal protostellar disks. We compute both the total amino acid abundance pattern and the relative frequencies of amino acids within the CM2 (e.g., Murchison) and CR2 chondrite subclasses based on Strecker reactions within these bodies. We match the relative frequencies to well within an order of magnitude among both CM2 and CR2 meteorites for parent body temperatures <200°C. These temperatures agree with 3D models of young planetesimal interiors. We find theoretical abundances of approximately 7 × 105 parts per billion, which is in agreement with the average observed abundance in CR2 meteorites of (4 ± 7) × 105, but an order of magnitude higher than the average observed abundance in CM2 meteorites of (2 ± 2) × 104. We find that the production of hydroxy acids could be favored over the production of amino acids within certain meteorite parent bodies (e.g., CI1, CM2) but not others (e.g., CR2). This could be due to the relatively lower NH3 abundances within CI1 and CM2 meteorite parent bodies, which leads to less amino acid synthesis. We also find that the water content in planetesimals is likely to be the main cause of variance between carbonaceous chondrites of the same subclass. We propose that amino acid abundances are primarily dependent on the ammonia and water content of planetesimals that are formed in chemically distinct regions within their natal protostellar disks.

Reference
Cobb AK, Pudritz RE, Pearce BKD (2015) Nature’s Starships. II. Simulating the Synthesis of Amino Acids in Meteorite Parent Bodies. Astrophysical Journal 809, 6.

Link to Article [doi:10.1088/0004-637X/809/1/6]

¹Thomas J. Zega, ^2,3Pierre Haenecour, ²Christine Floss, ⁴Rhonda M. Stroud
¹Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd, Tucson, AZ 85721-0092, USA
²Laboratory for Space Sciences and Physics Department, Washington University, One Brookings Drive, Campus Box 1105, St. Louis, MO 63130, USA
³Department of Earth and Planetary Sciences, Washington University, One Brookings Drive, Campus Box 1169, St. Louis, MO 63130, USA
⁴Materials Science and Technology Division, Code 6366, Naval Research Laboratory, 4555 Overlook Ave, SW Washington, DC 20375, USA

We report the first microstructural confirmation of circumstellar magnetite, identified in a petrographic thin section of the LaPaz Icefield 031117 CO3.0 chondrite. The O-isotopic composition of the grain indicates an origin in a low-mass (~2.2 M⊙), approximately solar metallicity red/asymptotic giant branch (RGB/AGB) star undergoing first dredge-up. The magnetite is a single crystal measuring 750 × 670 nm, is free of defects, and is stoichiometric Fe3O4. We hypothesize that the magnetite formed via oxidation of previously condensed Fe dust within the circumstellar envelope of its progenitor star. Using an empirically derived rate constant for this reaction, we calculate that such oxidation could have occurred over timescales ranging from approximately ~9000–500,000 years. This timescale is within the lifetime of estimates for dust condensation within RGB/AGB stars.

Reference
Zega TJ, Haenecour P, Floss C, Stroud RM (2015) Circumstellar Magnetite from the LAP 031117 CO3.0 Chondrite. Astrophysical Journal 808 55.
Link to Article [doi:10.1088/0004-637X/808/1/55]

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]