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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Kristin Leftwich^1,*, David L. Bish¹ and C.H. Chen²

¹Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405, U.S.A.
²Indiana University Molecular Structure Center, Indiana University, Bloomington, Indiana 47405, U.S.A.

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

Reference
Leftwich K, Bish DL and Chen CH (2013) Crystal structure and hydration/dehydration behavior of Na2Mg(SO4)2·16H2O: A new hydrate phase observed under Mars-relevant conditions. American Mineralogist 98:1772-1778.
[doi:10.2138/am.2013.4509]

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Juan A. Sanchez^a,*, Vishnu Reddy^b,1, Michael S. Kelley^c,1,2, Edward A. Cloutis^d, William F. Bottke^e, David Nesvorný^e, Michael P. Lucas^f, Paul S. Hardersen^g,1, Michael J. Gaffey^g,1, Paul A. Abell^h,1, Lucille Le Corre^b

^aMax Planck Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany
^bPlanetary Science Institute, 1700 East Fort Lowell Road, Tucson, Arizona 85719, USA
^cDepartment of Geology and Geography, Georgia Southern University, Statesboro, USA
^dDepartment of Geography, University of Winnipeg, Winnipeg, Manitoba, Canada
^eSouthwest Research Institute and NASA Lunar Science Institute, Boulder, USA
^fDepartment of Earth and Planetary Sciences, University of Tennessee, USA
^gDepartment of Space Studies, University of North Dakota, Grand Forks, USA
^hNASA Johnson Space Center, Houston, Texas, USA
¹Visiting Astronomer at the Infrared Telescope Facility, which is operated by the University of Hawaii under Cooperative Agreement No. NNX-08AE38A with the National Aeronautics and Space Administration, Science Mission Directorate, Planetary Astronomy Program.
²Planetary Science Division, Science Mission Directorate, NASA Headquarters, Washington, DC 20546, USA.

Olivine-dominated asteroids are a rare type of objects formed either in nebular processes or through magmatic differentiation. The analysis of meteorite samples suggest that at least 100 parent bodies in the main belt experienced partial or complete melting and differentiation before being disrupted. However, only a few olivine-dominated asteroids, representative of the mantle of disrupted differentiated bodies, are known to exist. Due to the paucity of these of objects in the main belt their origin and evolution have been a matter of great debate over the years. In this work we present a detailed mineralogical analysis of twelve olivine-dominated asteroids. We have obtained near-infrared (NIR) spectra (0.7 to 2.4 μm) of asteroids (246) Asporina, (289) Nenetta, (446) Aeternitas, (863) Benkoela, (4125) Lew Allen and (4490) Bamberry. Observations were conducted with the Infrared Telescope Facility (IRTF) on Mauna Kea, Hawai’i. This sample was complemented with spectra of six other olivine-dominated asteroids including (354) Eleonora, (984) Gretia, (1951) Lick, (2501) Lohja, (3819) Robinson and (5261) Eureka obtained by previous workers. Within our sample we distinguish two classes, one that we call pure-olivine asteroids, which are those whose spectra only exhibit the 1 μm feature, and another referred to as olivine-rich asteroids, whose spectra exhibit the 1 μm feature and a weak (Band II depth ~4%) 2 μm feature. For the pure-olivine asteroids the olivine chemistry was found to range from ~Fo₄₉ to Fo₇₀, consistent with the values measured for brachinites and R chondrites. In the case of the olivine-rich asteroids we determined their olivine and low-Ca pyroxene abundance using a new set of spectral calibrations derived from the analysis of R chondrites spectra. We found that the olivine abundance for these asteroids varies from 0.68 to 0.93, while the fraction of low-Ca pyroxene to total pyroxene ranges from 0.6 to 0.9. A search for dynamical connections between the olivine-dominated asteroids and asteroid families found no genetic link (of the type core-mantel-crust) between these objects.

Reference
Sanchez JA, Reddy V, Kelley MS, Cloutis CA, Bottke WF, Nesvorný D, Lucas MP, Hardersen PS, Gaffey MJ, Abell PA and Le Corre L (in press) Olivine-dominated Asteroids: Mineralogy and Origin. Icarus
[doi:10.1016/j.icarus.2013.10.006]
Copyright Elsevier

Link to Article

Stephen M. Seddio^1,*, Bradley L. Jolliff¹, Randy L. Korotev¹ and Ryan A. Zeigler²

¹Department of Earth and Planetary Sciences and the McDonnell Center for Space Sciences, Washington University, St. Louis, Missouri 63130, U.S.A.
²Astromaterials and Exploration Science Directorate, NASA, Johnson Space Center, mail code KT, 2101 NASA Pkwy, Houston, Texas 77058, U.S.A.

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

Reference
Seddio SM, Jolliff BL, Korotev RJ and Zeigler RA (2013) Petrology and geochemistry of lunar granite 12032,366-19 and implications for lunar granite petrogenesis. American Mineralogist 98:1697-1713.
[doi:10.2138/am.2013.4330]

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Tomohiro Usui^1,2,*, Hikaru Iwamori¹

¹Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, Japan
²Lunar and Planetary Institute, Universities Space Research Association, Houston, Texas, USA

Dawn has recently revealed that the surface of Vesta is heterogeneously covered by polymictic regoliths represented by mixtures of howardite, eucrite, and diogenite (HED) meteorites. Mixing relations of the HED suite are examined here using a new computational statistical approach of independent component analysis (ICA). We performed eight-component ICA (Si, Ti, Al, Cr, Fe, Mn, Mg, and Ca) for 209 HED bulk-rock compositions. The ICA results indicate that the HED bulk-rock compositions can be reduced into three independent components (IC) and these IC vectors can reasonably explain compositional variation, petrographic observations, and the mixing relations of the HED suite. The IC-1 vector represents a eucrite variation that extends from cumulate eucrite toward main-group (MG) and incompatible-element enriched eucrites. The IC-2 vector represents a compositional variation of howardites that extends from diogenites to MG-eucrites, indicating the well-known two-component mixing trend of diogenite and eucrite. The IC-3 vector represents a compositional variation defined by diogenites and olivine-bearing diogenites, suggesting mixing of olivine and orthopyroxene. Among the three ICs, the diogenite-eucrite mixing trend IC-2 is most statistically robust and dominates the compositional variations of the HED suite. Our ICA study further indicates that the combination of only three elements (Mg, Si, and Fe) approximates the eight-component ICA model, and that the limited number of resolvable γ-ray spectra obtained by the Dawn mission possibly discriminates olivine lithologies from the olivine-free regolith breccias on the surface of Vesta.

Reference
Usui T and Iwamori H (in press) Mixing relations of the howardite-eucrite-diogenite suite: A new statistical approach of independent component analysis for the Dawn mission. Meteoritics & Planetary Science
[doi:10.1111/maps.12205]
Published by arrangement with John Wiley & Sons

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M. L. Grange^1,*, A. A. Nemchin^1,2, R. T. Pidgeon¹

¹Department of Applied Geology, Western Australian School of Mines, Curtin University, Perth, Australia
²Swedish Museum of Natural History, Stockholm, Sweden

Zircon and phosphate grains from matrix and quartz-monzodiorite (QMD) clasts in two thin sections of Apollo 15 impact melt breccia 15405 were investigated using optical microscopy, scanning electron microscopy, Raman spectroscopy, and ion microprobe U-Pb analyses. U-Pb results for zircon grains with well-defined cathodoluminescence zoning define the primary (i.e., magmatic) crystallization age as 4330 ± 6 Ma (2σ). One zircon consists of a preserved inner part surrounded by a porous polycrystalline (“granular”) mixture of zircon and baddeleyite, indicating incomplete reaction of the zircon with melt. Previous work showed that this microstructure could form at pressures above 60 GPa and a temperature close to ~1700°C and is evidence of an impact-related melting event. The U-Pb system of this grain indicates a resetting event at 1940 ± 10 Ma, interpreted as the age of this impact (impact #1). Other zircon and phosphate grains also have disturbed U-Pb systems, showing an even younger reset event (impact #2) at 1407 ± 57 Ma. Evidence of impact is supported by microstructures of zircon and baddeleyite such as secondary rims. These impacts are tentatively identified as those having formed Autolycus and Aristillius craters.

Reference
Grange ML, Nemchin AA and Pidgeon RT (in press) The effect of 1.9 and 1.4 Ga impact events on 4.3 Ga zircon and phosphate from an Apollo 15 melt breccia. Journal of Geophysical Research – Planets
[doi:10.1002/jgre.20167]
Published by arrangement with John Wiley & Sons

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Richard A. Kerr

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

Reference
Kerr RA (in press) Roving Into Martian Waters. Science
[doi:10.1126/science.342.6156.304]

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