Akira Tsuchiyama

Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan

The Japanese spacecraft Hayabusa returned samples from the surface of an asteroid (near-Earth S-type asteroid 25143 Itokawa) for the first time in human history. This article describes the results of the initial analysis of the mineralogy, micropetrology, and elemental and isotopic compositions of regolith particles from Itokawa measuring 30–180 μm in diameter. The results show a direct link between ordinary chondrites and S-type asteroids. The regolith particles provide evidence of space-weathering rims and grain abrasion, and the information obtained has elucidated various processes on the airless surface of Itokawa, such as the impact of small objects, grain motion, and irradiation by solar wind.

Reference
Tsuchiyama A (2014) Asteroid Itokawa A Source of Ordinary Chondrites and A Laboratory for Surface Processes. Elements  10:45-50.
[doi:10.2113/gselements.10.1.45]
Copyright: The Mineralogical Society of America

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Harry Y. McSween¹, Maria Cristina De Sanctis², Thomas H. Prettyman³, Dawn Science Team

¹Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996-1410, USA
²Istituto di Astrofisica e Planetologia Spaziali, Istituto Nazionale de Astrofisica, Rome, Italy
³Planetary Science Institute, Tucson, AZ 85719, USA

Most asteroids are collisional rubble from eons past, and few of them have survived intact. Vesta, the second most massive asteroid, is the only differentiated, rocky body in this category. This asteroid provides a unique view of the kinds of planetesimals that accreted to form the terrestrial planets. We know more about this asteroid than any other, thanks to its recently completed exploration by the orbiting Dawn spacecraft and studies of the ~1000 meteorites derived from it. The synergy provided by in situ analyses and samples has allowed an unparalleled understanding of Vesta’s mineralogy, petrology, geochemistry, and geochronology.

Reference
McSween HY, De Sanctis MC, Prettyman TH and Dawn Science Team (2014) Unique, Antique Vesta. Elements  10:39-44.
[doi:10.2113/gselements.10.1.39]
Copyright: The Mineralogical Society of America

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Cyrena Goodrich¹, Addi Bischoff² and David P. O’Brien³

¹Planetary Science Institute, 1700 E. Ft. Lowell Drive, Tucson, AZ 85179, USA
²Institut für Planetologie, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
³Planetary Science Institute, 1700 E. Ft. Lowell Drive, Tucson, AZ 85179, USA

On October 6, 2008, the small (~4 m) asteroid 2008 TC₃ was discovered and predicted to hit Earth within ~19 hours. Photometric data and a reflectance spectrum were obtained. The asteroid fragmented at ~37 km altitude above Sudan. Approximately 700 centimeter-sized fragments were recovered and constitute the meteorite Almahata Sitta. It is a unique meteorite breccia, consisting of ~50–70% ureilitic materials, plus samples of nearly every major chondrite group. The reflectance spectrum of 2008 TC₃is closest to that of F-class asteroids, not previously associated with any meteorite type. 2008 TC₃/Almahata Sitta records a complex history of fragmentation, migration, and reaccretion of materials in the Solar System.

Reference
Goodrich C, Bischoff A and O’Brien DP (2014) Asteroid 2008 TC3 and the Fall of Almahata Sitta, a Unique Meteorite Breccia. Elements  10:31-37.
[doi:10.2113/gselements.10.1.31]
Copyright: The Mineralogical Society of America

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Rhian H. Jones^a, Francis M. McCubbin^a,b, Linda Dreeland^a, Yunbin Guan^c, Paul V. Burger^a,b Charles K. Shearer^a,b

^aDepartment of Earth and Planetary Sciences, MSC03 2040, University of New Mexico, Albuquerque, NM 87131, U.S.A.
^bInstitute of Meteoritics, MSC03 2050, University of New Mexico, Albuquerque, NM 87131, U.S.A.
^cDivision of Geological and Planetary Sciences, California Institute of Technology, MC 170-25, Pasadena, CA 91125, U. S. A.

Ordinary chondrites contain two phosphate minerals, merrillite and chlorapatite, both of which are secondary minerals that developed in response to metamorphism on the chondrite parent bodies. We have studied the phosphate mineralogy of four LL chondrites, of petrologic types 3.9 to 6, in order to determine the petrogenesis of the two minerals and interpret the conditions under which they formed. Characterization of merrillite and apatite includes textural observations, mineral compositions determined by electron probe microanalysis, and ion microprobe analyses of trace element and volatile anion elemental abundances. Initial formation of phosphate minerals during mild metamorphism, to petrologic type 4 conditions, resulted in oxidation of P that was originally incorporated in metal, and growth of merrillite as inclusions within metal grains. Subsequent development of both phosphate minerals occurred in response to diffusional equilibration, possible precipitation from fluids as well as replacement reactions resulting from interactions with fluids. Porosity and vein-filling textures in both merrillite and chlorapatite, as well as textures indicating replacement of merrillite by chlorapatite, support a model in which fluid played a significant role and suggest an interface-coupled dissolution-reprecipitation mechanism during metasomatism. Some associations of phosphate minerals with chromite-plagioclase assemblages suggest that phosphate minerals could also be related to impact processes, either as precipitation from an impact melt or as a result of interactions with a fluid or vapor derived from an impact melt. Fluid compositions may have been water-bearing initially, at low temperatures of metamorphism, but later evolved to become halogen-rich and very dry. Late-stage halogen-rich fluids that dominated during cooling of LL chondrite material may have been derived from vaporization of partial melts in the interior of the parent body. Overall, the LL chondrite parent body underwent a complex chemical evolution, in which metasomatism played a significant role.

Reference
Jones RH, McCubbin FM, Dreeland L, Guan Y, Burger PV and Shearer CK (in press) Phosphate Minerals in LL Chondrites: A Record of the Action of Fluids During Metamorphism on Ordinary Chondrite Parent Bodies. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2014.01.027]
Copyright Elsevier

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T. Kneissl^a et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

^aFreie Universitaet Berlin, Berlin, Germany

A variety of geologic landforms and features are observed within Quadrangle Av-13 Tuccia in the southern hemisphere of Vesta. The quadrangle covers parts of the highland Vestalia Terra as well as the floors of the large Rheasilvia and Veneneia impact basins, which results in a substantial elevation difference of more than 40 km between the northern and the southern portions of the quadrangle. Measurements of crater size-frequency distributions within and surrounding the Rheasilvia basin indicate that gravity-driven mass wasting in the interior of the basin has been important, and that the basin has a more ancient formation age than would be expected from the crater density on the basin floor alone. Subsequent to its formation, Rheasilvia was superimposed by several mid-sized impact craters. The most prominent craters are Tuccia, Eusebia, Vibidia, Galeria, and Antonia, whose geology and formation ages are investigated in detail in this work. These impact structures provide a variety of morphologies indicating different sorts of subsequent impact-related or gravity-driven mass wasting processes. Understanding the geologic history of the relatively young craters in the Rheasilvia basin is important in order to understand the even more degraded craters in other regions of Vesta.

Reference
Kneissl et al. (in press) Morphology and Formation Ages of Mid-Sized Post-Rheasilvia Craters – Geology of Quadrangle Tuccia, Vesta. Icarus
[doi:10.1016/j.icarus.2014.02.012]
Copyright Elsevier

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B. W. Grefenstette et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA

We do not have a copyright agreement with Nature, and therefore the abstract is currently only available from the link below.

Reference
Grefenstette et al. (2014) Asymmetries in core-collapse supernovae from maps of radioactive 44Ti in Cassiopeia A. Nature 506, 339–342.
[doi:10.1038/nature12997]

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J. Martin Laming

Space Science Division, Naval Research Laboratory, Washington DC 20375, USA.

We do not have a copyright agreement with Nature, and therefore the abstract is currently only available from the link below.

Reference
Laming JM (2014) Astrophysics: Lopsided stellar death. Nature 506, 298–299.
[doi:10.1038/506298a]

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Alexandra Witze

We do not have a copyright agreement with Nature, and therefore the abstract is currently only available from the link below.

Reference
Witze A (2014) Astronomy: Death of a comet. Nature 506, 281–283.
[doi:10.1038/506281a]

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Noël Chaumard^1,2,3,†, Bertrand Devouard^1,2,3,‡, Audrey Bouvier^4,§, Meenakshi Wadhwa⁴

¹Laboratoire Magmas et Volcans, Clermont Université, Université Blaise Pascal, Clermont-Ferrand, France
²CNRS, UMR 6524, LMV, Clermont-Ferrand, France
³IRD, R 163, LMV, Clermont-Ferrand, France
⁴Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA
^†Laboratoire de Minéralogie et de Cosmochimie du Muséum, Muséum National d’Histoire Naturelle, UMR 7202 – CNRS, Paris, France
^‡Aix-Marseille Université, CNRS, IRD, CEREGE UM34, Aix en Provence, France
^§University of Western Ontario, Department of Earth Sciences, London, Ontario, Canada

CK chondrites are the only group of carbonaceous chondrites with petrologic types ranging from 3 to 6. Although CKs are described as calcium-aluminum-rich inclusion (CAI)-poor objects, the abundance of CAIs in the 18 CK3–6 we analyzed ranges from zero to approximately 16.4%. During thermal metamorphism, some of the fine-grained CAIs recrystallized as irregular assemblages of plagioclase + Ca-rich pyroxene ± olivine ± Ca-poor pyroxene ± magnetite. Coarse-grained CAIs display zoned spinel, fassaite destabilization, and secondary grossular and spinel. Secondary anorthite, grossular, Ca-rich pyroxene, and spinel derive from the destabilization of melilite, which is lacking in all CAIs investigated. The Al-Mg isotopic systematics measured in fine- and coarse-grained CAIs from Tanezrouft (Tnz) 057 was affected by Mg redistribution. The partial equilibration of Al-Mg isotopic signatures obtained in the core of a coarse-grained CAI (CG1-CAI) in Tnz 057 may indicate a lower peak temperature for Mg diffusion of approximately 540–580 °C, while grossular present in the core of this CAI indicates a higher temperature of around 800 °C for the metamorphic event on the parent body of Tnz 057. Excluding metamorphic features, the similarity in nature and abundance of CAIs in CK and CV chondrites confirms that CVs and CKs form a continuous metamorphic series from type 3 to 6.

Reference
Chaumard N, Devouard B, Bouvier A and Wadhwa M (in press) Metamorphosed calcium-aluminum-rich inclusions in CK carbonaceous chondrites. Meteoritics & Planetary Science
[doi:10.1111/maps.12260]
Published by arrangement with John Wiley & Sons

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Edward A. Cloutis¹, Richard P. Binzel² and Michael J. Gaffey³

¹Department of Geography, University of Winnipeg, 515 Portage Avenue, Winnipeg, MB R3B 2E9, Canada
²Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 54-426, Cambridge, MA 02139, USA
³Department of Space Studies, University of North Dakota, Box 9008, Grand Forks, ND 58202-9008, USA

Asteroids are arguably the most accessible remnants of building blocks of the early Solar System and an essential piece of the terrestrial planet–formation puzzle. Determining their compositions and physical properties can provide important and otherwise unobtainable information concerning the origin, structure, and dynamic history of the Solar System, as well as insights into the sources of materials from which the terrestrial planets were constructed. Our understanding of the compositional structure of the asteroid belt and of individual asteroids has advanced significantly since the 1970s. Strong associations between asteroids and meteorites are emerging thanks to multitechnique observations, the synthesis of observations and modeling, in situ measurements, and sample-return missions.

Reference
Cloutis EA, Binzel RP and Gaffey MJ (2014) Establishing Asteroid–Meteorite Links. Elements  10:25-30.
[doi:10:11-17.10.2113/gselements.10.1.25]
Copyright: The Mineralogical Society of America

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