Masahiko Tanaka^1,*, Tomoki Nakamura², Takaaki Noguchi³, Aiko Nakato², Hatsumi Ishida², Toru Yada⁴, Kei Shirai⁴, Akio Fujimura⁴, Yukihiro Ishibashi⁴, Masanao Abe⁴, Tatsuaki Okada⁴, Munetaka Ueno⁴, Toshifumi Mukai⁴

¹Synchrotron X-ray Station at SPring-8, National Institute for Materials Science (NIMS), Sayo, Hyogo, Japan
²Department of the Earth and Planetary Material Science, Tohoku University, Sendai, Miyagi, Japan
³Department of Materials and Biological Sciences, Ibaraki University, Mito, Ibaraki, Japan
⁴JAXA-ISAS, Sagamihara, Kanagawa, Japan

The crystallization temperatures of Itokawa surface particles recovered by the space probe Hayabusa were estimated by a plagioclase geothermometer using sodic plagioclase triclinicity. The Δ131-index required for the thermometer, which is the difference in X-ray diffraction peak positions between the 131 and 131 reflections of plagioclase, was obtained by a high-resolution synchrotron Gandolfi camera developed for the third generation synchrotron radiation beamline, BL15XU at SPring-8. Crystallization temperatures were successfully determined from the Δ131-indices for four particles. The observed plagioclase crystallization temperatures were in a range from 655 to 660 °C. The temperatures indicate crystallization temperatures of plagioclases in the process of prograde metamorphism before the peak metamorphic stage.

Reference
Tanaka M, Nakamura T, Noguchi T, Nakato A, Ishida H, Yada T, Shirai K, Fujimura A, Ishibashi Y, Abe M, Okada T, Ueno M and Mukai T (in press) Crystallization temperature determination of Itokawa particles by plagioclase thermometry with X-ray diffraction data obtained by a high-resolution synchrotron Gandolfi camera. Meteoritics & Planetary Science
[doi:10.1111/maps.12215]
Published by arrangement with John Wiley & Sons

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W. Akram^1,2, M. Schönbächler^1,2, P. Sprung³, and N. Vogel^2,4

¹School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK
²Institute for Geochemistry and Petrology, ETH, Clausiusstrasse 25, 8092 Zürich, Switzerland
³Institut für Planetologie, Universität Münster, Wilhelm-Klemm-Strasse 10, D-48149 Münster, Germany
⁴Eawag, Swiss Federal Institute of Aquatic Science and Technology, Water Resources and Drinking Water, Ueberlandstrasse 133, 8600 Dübendorf, Switzerland

Recent work based on analyses of meteorite and terrestrial whole-rock samples showed that the r- and s- process isotopes of Hf were homogeneously distributed throughout the inner solar system. We report new Hf isotope data for Calcium-Aluminum-rich inclusions (CAIs) of the CV3 carbonaceous chondrite Allende, and novel high-precision Zr isotope data for these CAIs and three carbonaceous chondrites (CM, CO, CK). Our Zr data reveal enrichments in the neutron-rich isotope ⁹⁶Zr (≤1ε in ⁹⁶Zr/⁹⁰Zr) for bulk chondrites and CAIs (~2ε). Potential isotope effects due to incomplete sample dissolution, galactic and cosmic ray spallation, and the nuclear field shift are assessed and excluded, leading to the conclusion that the ⁹⁶Zr isotope variations are of nucleosynthetic origin. The ⁹⁶Zr enrichments are coupled with ⁵⁰Ti excesses suggesting that both nuclides were produced in the same astrophysical environment. The same CAIs also exhibit deficits in r-process Hf isotopes, which provides strong evidence for a decoupling between the nucleosynthetic processes that produce the light (A ≤ 130) and heavy (A > 130) neutron-rich isotopes. We propose that the light neutron-capture isotopes largely formed in Type II supernovae (SNeII) with higher mass progenitors than the supernovae that produced the heavy r-process isotopes. In the context of our model, the light isotopes (e.g. ⁹⁶Zr) are predominantly synthesized via charged-particle reactions in a high entropy wind environment, in which Hf isotopes are not produced. Collectively, our data indicates that CAIs sampled an excess of materials produced in a normal mass (12-25 M_☉) SNII.

Reference
Akram W, Schönbächler M, Sprung P and Vogel N (2013) Zirconium—Hafnium Isotope Evidence from Meteorites for the Decoupled Synthesis of Light and Heavy Neutron-rich Nuclei. The Astrophysical Journal 777:169.
[doi:10.1088/0004-637X/777/2/169]

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Subrata Chakraborty^*, Petia Yanchulova, Mark H. Thiemens

Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093–0356, USA.

We currently seek a copyright agreement with Science to display abstracts of their cosmochemistry related publications.

Reference
Chakraborty S, Yanchulova P and Thiemens MH (in press) Mass-Independent Oxygen Isotopic Partitioning During Gas-Phase SiO2 Formation. Science 342:463-466.
[doi:10.1126/science.1242237]

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Florian J. Zurfluh^1,*, Beda A. Hofmann², Edwin Gnos³, Urs Eggenberger¹

¹Institut für Geologie, Universität Bern, Bern, Switzerland
²Naturhistorisches Museum der Burgergemeinde Bern, Bern, Switzerland
³Muséum d’histoire naturelle de la Ville de Genève, Genève 6, Switzerland

The common appearance of hygroscopic brine (“sweating”) on ordinary chondrites (OCs) from Oman during storage under room conditions initiated a study on the role of water-soluble salts on the weathering of OCs. Analyses of leachates from OCs and soils, combined with petrography of alteration features and a 11-month record of in situ meteorite and soil temperatures, are used to evaluate the role of salts in OC weathering. Main soluble ions in soils are Ca²⁺, SO₄²⁻, HCO₃⁻, Na⁺, and Cl⁻, while OC leachates are dominated by Mg²⁺ (from meteoritic olivine), Ca²⁺ (from soil), Cl⁻ (from soil), SO₄²⁻ (from meteoritic troilite and soil), and iron (meteoritic). “Sweating meteorites” mainly contain Mg²⁺ and Cl⁻. The median Na/Cl mass ratio of leachates changes from 0.65 in soils to 0.07 in meteorites, indicating the precipitation of a Na-rich phase or loss of an efflorescent Na-salt. The total concentrations of water-soluble ions in bulk OCs ranges from 600 to 9000 μg g⁻¹ (median 2500 μg g⁻¹) as compared to 187–14140 μg g⁻¹ in soils (median 1148 μg g⁻¹). Soil salts dissolved by rain water are soaked up by meteorites by capillary forces. Daily heating (up to 66.3 °C) and cooling of the meteorites cause a pumping effect, resulting in a strong concentration of soluble ions in meteorites over time. The concentrations of water-soluble ions in meteorites, which are complex mixtures of ions from the soil and from oxidation and hydrolysis of meteoritic material, depend on the degree of weathering and are highest at W3. Input of soil contaminants generally dominates over the ions mobilized from meteorites. Silicate hydrolysis preferentially affects olivine and is enhanced by sulfide oxidation, producing local acidic conditions as evidenced by jarosite. Plagioclase weathering is negligible. After completion of troilite oxidation, the rate of chemical weathering slows down with continuing Ca-sulfate contamination.

Reference
Zurfluh FJ, Hofmann BA, Gnos E and Eggenberger U (in press) “Sweating meteorites”—Water-soluble salts and temperature variation in ordinary chondrites and soil from the hot desert of Oman. Meteoritics & Planetary Science
[doi:10.1111/maps.12211]
Published by arrangement with John Wiley & Sons

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M. Jadhav¹, M. Pignatari^2,6, F. Herwig^3,6,7, E. Zinner⁴, R. Gallino⁵ and G. R. Huss¹

¹Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Mānoa, Honolulu, HI 96822, USA
²Department of Physics, University of Basel, CH-4056 Basel, Switzerland
³Department of Physics & Astronomy, University of Victoria, Victoria, BC V8P5C2, Canada
⁴Laboratory for Space Sciences & the Physics Department, Washington University, St. Louis, MO 63130, USA
⁵Dipartimento di Fisica Generale, Università di Torino & INAF, Via Pietro Giuria 1, 10125 Torino, Italy
⁶NuGrid Collaboration: http://www.nugridstars.org.
⁷Also at The Joint Institute for Nuclear Astrophysics, Notre Dame, IN 46556, USA.

Graphite is one of the many presolar circumstellar condensate species found in primitive meteorites. While the isotopic compositions of low-density graphite grains indicate an origin in core-collapse supernovae, some high-density grains have extreme isotopic anomalies in C, Ca, and Ti, which cannot be explained by envelope predictions of asymptotic giant branch (AGB) stars or theoretical supernova models. The Ca and Ti isotopic anomalies, however, match the predictions of He-shell abundances in AGB stars. In this study, we show that the C, Ca, and Ti isotopic anomalies are consistent with nucleosynthesis predictions of the H-ingestion phase during a very late thermal pulse (VLTP) event in post-AGB stars. The low ¹²C/¹³C isotopic ratios in these grains are a result of abundant ¹²C efficiently capturing the protons that are being ingested during the VLTP. Very high neutron densities of ~10¹⁵ cm⁻³, typical of the i-process, are achieved during this phase in post-AGB stars. The large ^42,43,44Ca excesses in some graphite grains are indicative of neutron capture nucleosynthesis during VLTP. The comparison of VLTP nucleosynthesis calculations to the graphite data also indicate that apparent anomalies in the Ti isotopic ratios are due to large contributions from ^46,48Ca, which cannot be resolved from the isobars ^46,48Ti during the measurements. We conclude that presolar graphite grains with moderate to extreme Ca and Ti isotopic anomalies originate in post-AGB stars that suffer a VLTP.

Reference
Jadhav M, Pignatari M, Herwig F, Zinner E, Gallino R, and Huss GR (in press) Relics of Ancient Post-AGB Stars in a Primitive Meteorite. The Astrophysical Journal – Letters
[doi:10.1088/2041-8205/777/2/L27]

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Emma C. Marcucci^1,2, Brian M. Hynek^1,2,*, Kathryn S. Kierein-Young², K. L. Rogers^3,4

¹Department of Geological Sciences, University of Colorado Boulder, Boulder, Colorado, USA
²Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, Colorado, USA
³Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC, USA
⁴Now at Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, New York, USA

Acid-sulfate weathering at Nicaraguan hydrothermal sites Cerro Negro, Momotombo, and Telica volcanoes and Hervidores de San Jacinto mudpots was characterized as an analog for similar processes that likely operated on early Mars. In situ mineralogical analyses were conducted with a field portable visible near-infrared spectrometer for comparison to similar Martian data sets. Three classes of alteration minerals were identified: sulfates (gypsum and natroalunite), oxides/hydroxides (hematite and goethite), and phyllosilicates (kaolinite/halloysite, montmorillonite, and saponite), as well as elemental sulfur and hydrated silica phases. Our sites had similar suites of minerals, but frequencies varied with location. The results of this field campaign allow inferences regarding the paleo-environmental conditions that were likely present at similar relic hydrothermal sites identified on Mars. In particular, sulfates and phyllosilicates could have coevolved under hydrothermal conditions at Noctis Labyrinthus as is seen in Nicaragua. Fe/Mg smectites were detected in areas with pH of 3–4. Alunite spectra at Terra Sirenum demonstrated mineral mixing effects on spectroscopy. Mineral mixing can cause uncertainties in spectral identification due to a dominant spectrum, such as iron minerals, masking another or the suppression of weaker bands. When viewed from orbit, our field sites would likely be dominated by hydrated silica and Mars sites, such as one in Syrtis Major, could have a more diverse mineralogy than the data reveal. Concentrated amorphous silica, such as at Gusev crater, can result from acidic fumarolic activity, while Mg sulfates may indicate a lack of reworking by water. This field spectroscopy study helps confirm and provide insight into hydrothermal processes on ancient Mars.

Reference
Marcucci EC, Hynek BM, Kierein-Young KS and Rogers KL (in press) Visible-near-infrared reflectance spectroscopy of volcanic acid-sulfate alteration in Nicaragua: Analogs for early Mars. Journal of Geophysical Research – Planets
[doi:10.1002/jgre.20159]
Published by arrangement with John Wiley & Sons

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Tomáš Magna^a,*, Magdalena Šimčíková^a, Frédéric Moynier^b

^aCzech Geological Survey, Klárov 3, CZ-118 21 Prague 1, Czech Republic
^bUniversité Paris Diderot, 1 rue Jussieu, F-75238 Paris cedex 05, France

We present lithium (Li) abundances and isotope compositions in a suite of howardites, eucrites and diogenites (HEDs). These meteorites most likely originated from asteroid Vesta and were delivered to Earth by a series of independent impact events. The Li concentrations show striking differences between Li-poor diogenites plus cumulate eucrites and Li-enriched eucrites whilst howardites have Li abundances intermediate between eucrites and diogenites. Contrary to Li elemental inter-group differences, Li isotope compositions are irresolvable among these individual groups of HED meteorites despite their wildly distinct petrography, attesting to insignificant Li isotope fractionation during formation of a thick basaltic crust by melting of the Vestan mantle. The mean Li isotope composition of Bulk Silicate Vesta is estimated at 3.7 ± 0.6‰ (1σ), intermediate to that of the Earth versus Mars and Moon but identical with these terrestrial bodies within uncertainty. This further validates largely homogeneous inner Solar System solids from the Li isotope perspective and supports the lack of loss of moderately volatile elements from planetary embryos during their magmatic histories because Li does not follow depletion trends inferred from more volatile elements. Pasamonte eucrite has the same Li isotope composition of other eucrites although it may not be directly linked to Vesta. These observations are also important for generating Li elemental and isotope signatures in juvenile basaltic crusts of large terrestrial planets and numerous planetary embryos in the early Solar System. A combination of CV+L chondrites may be less suitable for building Vesta from Li perspective but this may face sampling bias of available data and only further analyses may resolve this issue. Alternatively, significant shift of ~1‰ towards heavier Li isotope compositions must have occurred during thermal processing of CV+L (2.2 to 2.8‰) mixture in order to account for the observed Li isotope systematics in HED meteorites. No correlation is observed between Li versus Zn, Fe or Si isotopes, respectively, implying unrelated processes of forming stable isotope variations observed in HED meteorites.

Reference
Magna T, Šimčíková M and Moynier F (in press) Lithium systematics in howardite–eucrite–diogenite meteorites: Implications for crust–mantle evolution of planetary embryos. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2013.10.015]
Copyright Elsevier

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M. Pajola^1,5, M. Lazzarin², C. M. Dalle Ore^3,4, D. P. Cruikshank⁴, T. L. Roush⁴, S. Magrin¹, I. Bertini¹, F. La Forgia², and C. Barbieri^1,2

¹Center of Studies and Activities for Space, CISAS, “G. Colombo,” University of Padova, I-35131 Padova, Italy
²Department of Physics and Astronomy, University of Padova, I-35131 Padova, Italy
³Carl Sagan Center, SETI Institute, Mountain View, CA 94043, USA
⁴NASA Ames Research Center, Moffett Field, CA 94035, USA
⁵Currently (2012-2013) Visiting Scientist at NASA Jet Propulsion Laboratory, JPL-CALTECH, 4800 Oak Grove Drive, Pasadena, CA 91109, USA.

This paper describes the spectral modeling of the surface of Phobos in the wavelength range between 0.25 and 4.0 μm. We use complementary data to cover this spectral range: the OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System on board the ESA Rosetta spacecraft) reflectance spectrum that Pajola et al. merged with the VSK-KRFM-ISM (Videospectrometric Camera (VSK)-Combined Radiometer and Photometer for Mars (KRFM)-Imaging Spectrometer for Mars (ISM) on board the USSRPhobos 2 spacecraft) spectra by Murchie & Erard and the IRTF (NASA Infrared Telescope Facility, Hawaii, USA) spectra published by Rivkin et al. The OSIRIS data allow the characterization of an area of Phobos covering from 868 N to 90° S in latitude and from 126° W to 286° W in longitude. This corresponds chiefly to the trailing hemisphere, but with a small sampling of the leading hemisphere as well. We compared the OSIRIS results with the Trojan D-type asteroid 624 Hektor and show that the overall slope and curvature of the two bodies over the common wavelength range are very similar. This favors Phobos being a captured D-type asteroid as previously suggested. We modeled the OSIRIS data using two models, the first one with a composition that includes organic carbonaceous material, serpentine, olivine, and basalt glass, and the second one consisting of Tagish Lake meteorite and magnesium-rich pyroxene glass. The results of these models were extended to longer wavelengths to compare the VSK-KRFM-ISM and IRTF data. The overall shape of the second model spectrum between 0.25 and 4.0 μm shows curvature and an albedo level that match both the OSIRIS and Murchie & Erard data and the Rivkin et al. data much better than the first model. The large interval fit is encouraging and adds weight to this model, making it our most promising fit for Phobos. Since Tagish Lake is commonly used as a spectral analog for D-type asteroids, this provides additional support for compositional similarities between Phobos and D-type asteroids.

Reference
Pajola M, Lazzarin M, Dalle Ore CM, Cruikshank DP, Roush TL, Magrin S, Bertini I, La Forgia F and Barbieri C (in press) Phobos as a D-type Captured Asteroid, Spectral Modeling from 0.25 to 4.0 μm. The Astrophysical Journal
[doi:10.1088/0004-637X/777/2/127]

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A. Moór¹, A. Juhász², Á. Kóspál^3,10, P. Ábrahám¹, D. Apai⁴, T. Csengeri⁵, C. Grady^6,7, Th. Henning⁸, A. M. Hughes⁹, Cs. Kiss¹, I. Pascucci⁴, M. Schmalzl², and K. Gabányi¹

¹Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, P.O. Box 67, H-1525 Budapest, Hungary
²Leiden Observatory, Leiden University, Niels Bohrweg 2, NL-2333-CA Leiden, The Netherlands
³Research and Scientific Support Department, European Space Agency (ESA-ESTEC, SRE-SA), P.O. Box 299, 2200-AG Noordwijk, The Netherlands
⁴Department of Astronomy and Department of Planetary Sciences, The University of Arizona, Tucson, AZ 85721, USA
⁵Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
⁶NASA Goddard Space Flight Center, Code 667, Greenbelt, MD 20771, USA
⁷Eureka Scientific, 2452 Delmer Street, Suite 100, Oakland, CA 94602, USA
⁸Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany
⁹Wesleyan University Department of Astronomy, Van Vleck Observatory, 96 Foss Hill Dr., Midletown, CT 06457, USA
¹⁰ESA fellow.

Circumstellar disks around stars older than 10 Myr are expected to be gas-poor. There are, however, two examples of old (30-40 Myr) debris-like disks containing a detectable amount of cold CO gas. Here we present Atacama Large Millimeter/Submillimeter Array (ALMA) and Herschel Space Observatory observations of one of these disks, around HD 21997, and study the distribution and origin of the dust and its connection to the gas. Our ALMA continuum images at 886 μm clearly resolve a broad ring of emission within a diameter of ~4.”5, adding HD 21997 to the dozen debris disks resolved at (sub)millimeter wavelengths. Modeling the morphology of the ALMA image with a radiative transfer code suggests inner and outer radii of ~55 and ~150 AU, and a dust mass of 0.09 M _⊕. Our data and modeling hints at an extended cold outskirt of the ring. Comparison with the morphology of the CO gas in the disk reveals an inner dust-free hole where gas nevertheless can be detected. Based on dust grain lifetimes, we propose that the dust content of this gaseous disk is of secondary origin and is produced by planetesimals. Since the gas component is probably primordial, HD 21997 is one of the first known examples of a hybrid circumstellar disk, a thus-far little studied late phase of circumstellar disk evolution.

Reference
Moór A, Juhász A, Kóspál Á, Ábrahám P, Apai D, Csengeri T, Grady C, Henning Th, Hughes AM, Kiss Cs, Pascucci I, Schmalzl M, and Gabányi K (in press) ALMA Continuum Observations of a 30 Myr Old Gaseous Debris Disk around HD 21997. The Astrophysical Journal – Letters
[doi:10.1088/2041-8205/777/2/L25]

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Gregory A. Brennecka^a,b,1, Lars E. Borg^a and Meenakshi Wadhwa^b

^aLawrence Livermore National Laboratory, Livermore, CA 94550
^bSchool of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404

The isotopic composition of our Solar System reflects the blending of materials derived from numerous past nucleosynthetic events, each characterized by a distinct isotopic signature. We show that the isotopic compositions of elements spanning a large mass range in the earliest formed solids in our Solar System, calcium–aluminum-rich inclusions (CAIs), are uniform, and yet distinct from the average Solar System composition. Relative to younger objects in the Solar System, CAIs contain positive r-process anomalies in isotopes A < 140 and negative r-process anomalies in isotopes A > 140. This fundamental difference in the isotopic character of CAIs around mass 140 necessitates (i) the existence of multiple sources for r-process nucleosynthesis and (ii) the injection of supernova material into a reservoir untapped by CAIs. A scenario of late supernova injection into the protoplanetary disk is consistent with formation of our Solar System in an active star-forming region of the galaxy.

Reference
Brennecka GA, Borg LE and Wadhwa M (2013) Evidence for supernova injection into the solar nebula and the decoupling of r-process nucleosynthesis. PNAS 110:17241-17246.
[doi:10.1073/pnas.1307759110 ]

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