¹Noriyuki Kawasaki, ¹Chizu Kato, ¹Shoichi Itoh, ¹Shigeyuki Wakaki, ²Motoo Ito, ¹Hisayoshi Yurimoto
¹Department of Natural History Sciences, Hokkaido University, Sapporo, 060-0810, Japan
²Kochi Institute for Core Sample Research, JAMSTEC B200, Monobe, Nankoku, Kochi, 783-8502, Japan

Disequilibrium oxygen isotopic distributions of Ca-Al-rich inclusions (CAIs) correspond to multiple melting events in the solar nebula. 26Al-26Mg systematics may be applicable for age differences among such melting events. We have carried out a coordinated study of detailed petrographic observations and in-situ oxygen and magnesium isotope measurements for a Type C CAI, EK1-04-2, from the Allende CV3 meteorite to determine the melting events and their ages. The CAI consists mainly of spinel, anorthite, olivine, and pyroxene, and has a core and mantle structure. Petrography of the core suggests that the crystallization sequence of the core minerals is from spinel, anorthite, olivine, and to pyroxene. The mantle has the same mineral assemblage as the core, and shows incomplete melting and solidification textures. Oxygen isotopic compositions of the minerals are distributed along the carbonaceous chondrite anhydrous mineral (CCAM) line (δ18O = −44 to +9‰), which indicates to preserve a chemical disequilibrium status in the CAI. Spinel shows a 16O-rich signature (δ18O ∼ −43‰), while anorthite is 16O-poor (δ18O ∼ +8‰). Olivine and pyroxene in the core have the same oxygen isotopic composition (δ18O ∼ −15‰), which indicates their equilibrium. Olivine and pyroxene in the mantle have variable oxygen isotopic compositions and are slightly depleted in 16O (δ18O = −13 to −4‰) compared with the same minerals in the core. The 26Al-26Mg systematics is consistent with the disequilibrium status observed according to the petrography and oxygen isotopes. Spinel is plotted on a line of (26Al/27Al)0 = (3.5 ± 0.2) × 10−5, anorthite is plotted on a line of (−1 ± 5) × 10−7, and olivine and pyroxene in the core are plotted on a line of (−1 ± 7) × 10−6. Plots of olivine and pyroxene in the mantle are scattered below the isochron of these minerals in the core. This study indicates that the EK1-04-2 Type C CAI underwent multiple heating events after the formation of its CAI precursor. The precursor CAI was formed ∼0.4 Myr after the formation of the Solar System defined by canonical CAI formation. At least 1.6 Myr after the precursor CAI formation, the CAI was partially melted and the melt exchanged oxygen isotopes with surrounding 16O-poor nebular gas. 16O-poor olivine and pyroxene in the core crystallized from the melt. Subsequently, Al-rich chondrules accreted onto the CAI, and the CAI experienced partial melting again and recrystallized to form the mantle. The oxygen and magnesium isotopes in anorthite were redistributed during thermal metamorphism in the Allende parent body. Our study reveals that the CAI had been retained in the solar nebula for at least 1.6 Myr and underwent multiple melting events in the nebula, and oxygen and 26Al-26Mg systematics has been partially disturbed depending on crystal sizes by metamorphism on the parent body.

Reference
Kawasaki N, Kato C, Itoh S, Wakaki S, Ito M, Yurimotoa H (2015) 26Al-26Mg chronology and oxygen isotope distributions of multiple melting for a Type C CAI from Allende. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.07.037]

Copyright Elsevier

^1,2Hsin-Wei Chen, ^1,3Typhoon Lee, ¹Der-Chuen Lee, ¹Jiang-Chang Chen
¹Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan, ROC
²School of Earth Sciences, University of Bristol, Bristol, UK
³Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan, ROC

Precise determinations of 48Ca anomalies in Allende calcium–aluminum-rich inclusions (CAIs) are reported in this work. There are endemic positive 48Ca/44Ca anomalies in all analyzed CAIs after normalization to 42Ca/44Ca, and it is clearly shown that there is no simple correlation between 48Ca/44Ca and 50Ti/48Ti anomalies, in agreement with Jungck et al. Compared to the 48Ca/44Ca versus 50Ti/48Ti correlation line defined by differentiated meteorites, reported by Chen et al., the CAIs plot to elevated 50Ti/48Ti. Assuming the 48Ca/44Ca anomalies of both CAIs and differentiated meteorites came from the same source, excess 50Ti anomalies in CAIs can be calculated by subtracting the part associated with 48Ca/44Ca. These excesses show a linear correlation with 138La anomalies, a neutrino-process nuclide. According to current stellar nucleosynthetic models, we therefore suggest that the solar system 48Ca, 50Ti, and 138La isotopic variations are made of mixtures between grains condensed from ejecta of neutron-rich accretion-induced SNe Ia and the O/Ne–O/C zone of core-collapse SNe II.

Reference
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]

¹Jean-Philippe Combe, ^2,3Eleonora Ammannito,²Federico Tosi, ²Maria Cristina de Sanctis, ¹Thomas B. McCord, ⁴Carol A. Raymond,³Christopher T. Russell
¹Bear Fight Institute, 22 Fiddler’s Road, P.O. Box 667, Winthrop, WA 98862, USA
²Istituto di Astrofisica e Planetologia Spaziali-Istituto Nazionale di Astrofisica, Rome, Italy
³Institute of Geophysics and Planetary Physics, University of California Los Angeles, CA, USA
⁴Jet Propulsion Laboratory, Pasadena, CA, USA

Vesta’s surface albedo variations and hydrated material content share similar spatial distribution. This observation is consistent with carbonaceous chondrite meteorites as a likely source material for dark surface units observed by the Dawn spacecraft, as presented by numerous publications. While these deposits have been studied extensively by analysis of data from the Framing Camera (FC) and the Visible and Infrared Spectrometer (VIR), we performed a new analysis based on an improved calibration of VIR. First we identified instrument and calibration artifacts, and we therefore developed corrections of the VIR flat field and response function. Then we developed a photometric correction for Vesta based on the lunar model by Shkuratov et al. (1999, Icarus 141), and a semi-analytical inversion of the photometric parameters. This photometric model combines minimization of the scattering effects due to the topography (a disk function) and variations of multiple-scattering with phase angle (the phase function) caused by microscopic physical properties of the regolith. The improved calibration and photometric correction enable more accurate analysis of the spectral properties of Vesta’s surface material, especially the reflectance at 1.4 μm and the 2.8 μm hydroxyl absorption band depth. We produced global and quadrangle maps that are used as a common dataset for this Icarus special issue on Vesta’s surface composition. The joint interpretation of both the 1.4 μm reflectance and the 2.8 μm absorption band depth reveals unusual spectral properties for a number of impact craters and ejecta compared to the rest of Vesta. An area including the Bellicia, Arruntia and Pomponia craters, where olivine might be present, has relatively high reflectance and a strong hydroxyl absorption band. Another area in the vicinity of Capparonia crater has a high content of hydrated materials, although with moderate reflectance and typical pyroxene-rich composition. Ejecta blankets west of Oppia crater have a spectral behavior similar to Capparonia, except for the wider and more complex shape of the hydroxyl absorption band. On the other hand, some low-hydrated areas associated to crater floors and ejecta have higher reflectance and steeper spectral slope than most low-hydrated terrains Vesta. A broad lane that extends from Rheasilvia rim at Matronalia Rupes to the northern regions hosts little to no hydrated materials and exhibits a moderate spectral slope, similar to Rheasilvia’s basin floor. These properties reinforce the hypothesis that the lane is composed of ejecta from Rheasilvia, as indicated by the distribution of pyroxene compositions by previous results from Dawn. A few small and fresh craters exhibit an association between low-reflectance, little to no hydrated materials and a strong positive spectral slope, suggesting optical effects by opaque coatings, as opposed to carbonaceous chondrite deposits, and possible coarser grains.

Reference
Combe J-P, Ammannito E, Tosi F, de Sanctis MC, McCord TB, Raymond CA, Russell CT (2015)
Reflectance properties and hydrated material distribution on Vesta: Global investigation of variations and their relationship using improved calibration of Dawn VIR mapping spectrometer. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.07.034]
Copyright Elsevier

^1,2Vladimir V. Busarev, ³Sergey I. Barabanov, ³Vyacheslav S. Rusakov, ²Vasiliy B. Puzin, ^1,4Valery V. Kravtsov
¹Lomonosov Moscow State University, Sternberg Astronomical Institute, University Avenue 13, 119992 Moscow, Russia
²Institute of Astronomy of Russian Academy of Science, Pyatnitskaya St. 48, 109017 Moscow, Russia
³Division of Mossbauer Spectroscopy, Physical Dep. of Lomonosov Moscow State University, 119992 Moscow, Russia
⁴Departamento de Fisica, Facultad de Ciencias Naturales, Universidad de Atacama, Copayapu 485, Copiapo, Chile

Six asteroids including two NEAs, one of which is PHA, accessible for observation in September 2012 were investigated using a low-resolution (R ≈ 100) spectrophotometry in the range 0.35-0.90 μm with the aim to study features of their reflectance spectra. A high-altitude position of our Terskol observatory (3150 m above sea level) favorable for the near-UV and visible-range observations of celestial objects let us probably to detect some new spectral features of the asteroids. Two subtle absorption bands centered at 0.53 and 0.74 μm were found in the reflectance spectra of S-type (32) Pomona and interpreted as signs of presence of pyroxenes in the asteroid surface matter and its different oxidation. Very similar absorption bands centered at 0.38, 0.44 and 0.67-0.71 μm have been registered in the reflectance spectra of (145) Adeona, (704) Interamnia, and (779) Nina of primitive types. We performed laboratory investigations of ground samples of known carbonaceous chondrites, Orguel (CI), Mighei (CM2), Murchison (CM2), Boriskino (CM2), and seven samples of low-iron Mg serpentines as possible analogs of the primitive asteroids. In the course of this work, we discovered an intense absorption band (up to ∼25%) centered at 0.44 μm in reflectance spectra of the low-Fe serpentine samples. As it turned out, the equivalent width of the band has a high correlation with content of Fe3+ (octahedral and tetrahedral) in the samples. It may be considered as a confirmation of the previously proposed mechanism of the absorption due to electronic transitions in exchange-coupled pairs (ECP) of Fe3+neighboring cations. It means that the absorption feature can be used as an indicator of ferric iron in oxidized and hydrated low-Fe compounds on the surface of asteroids and other atmosphereless celestial bodies. Moreover, our measurements showed that the mechanism of light absorption is partially or completely blocked in the case of intermediate to high iron contents. Therefore, the method cannot probably be used for quantitative estimation of Fe3+ content on the bodies. Based on laboratory study of the analog samples, we conclude that spectral characteristics of Adeona, Interamnia, and Nina correspond to a mixture of CI-CM-chondrites and hydrated silicates, oxides and/or hydroxides. Spectral signs of sublimation activity on Adeona, Interamnia, and Nina at minimal heliocentric distances are likely discovered in the short-wavelength range (∼0.4-0.6 μm). It is suggested that such cometary-like activity at the highest surface temperatures is a frequent phenomenon for C and close type asteroids including considerable amounts of ices beneath the surface. A usual way of origin of a temporal coma of ice particles around a primitive asteroid is excavated fresh ice at recent impuct event(s).

The obtained reflectance spectra of two NEAs, (330825) 2008 XE3 and 2012 QG42, are predominantly featureless and could be attributed to S(C) and S(B)-type bodies, respectively. We discuss reasons why weak spectral features seen in reflectance spectra of the main-belt asteroids are not observed in those of NEAs.

Reference
Busarev VV, Barabanov SI, Rusakov VS, Puzin VB, Kravtsov VV (2015) Spectrophotometry of (32) Pomona, (145) Adeona, (704) Interamnia, (779) Nina, (330825) 2008 XE3, and 2012 QG42 and laboratory study of possible analog samples. Icarus (in Press)
Linkt to Article [doi:10.1016/j.icarus.2015.08.001]
Copyright Elsevier

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