^1,2Selby Cull, ^2,3Patrick C. McGuire, ²Christoph Gross, ¹Jenna Myers, ¹Nina Shmorhun
¹Department of Geology, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010, USA
²Planetary Sciences and Remote Sensing Group, Institute of Geological Sciences, Department of Earth Sciences, Freie Universitaet Berlin, Berlin 12249, Germany
³Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland 20723, USA

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Reference
Cull S, McGuire PC, Gross C, Myers J, Shmorhun N (2014) A new type of jarosite deposit on Mars: Evidence for past glaciation in Valles Marineris? Geology 42, 59-962
Link to Article [doi:10.1130/G36152.1]

¹David W. Mittlefehldt
¹XI3/Astromaterials Research Office, Astromaterials Research and Exploration Sciences Division, NASA/Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058, USA

The howardite, eucrite and diogenite (HED) clan of meteorites are ultramafic and mafic igneous rocks and impact-engendered fragmental debris derived from a thoroughly differentiated asteroid. Earth-based telescopic observation and data returned from vestan orbit by the Dawn spacecraft make a compelling case that the asteroid (4) Vesta is the parent asteroid of HEDs, although this is not universally accepted. Diogenites are petrologically diverse and include dunitic, harzburgitic and noritic lithologic types in addition to the traditional orthopyroxenites. Diogenites form the lower crust of Vesta. Cumulate eucrites are gabbroic rocks formed by accumulation of pigeonite and plagioclase from a mafic magma at depth within the crust, while basaltic eucrites are melt compositions that likely represent shallow-level dikes and sills, and flows. Some basaltic eucrites are richer in incompatible trace elements compared to most eucrites, and these may represent mixed melts contaminated by partial melts of the mafic crust. Differentiation occurred within a few Myr of formation of the earliest solids in the Solar System. Evidence from oxygen isotope compositions and siderophile element contents favor a model of extensive melting of Vesta forming a global magma ocean that rapidly (period of a few Myr) segregated and crystallized to yield a metallic core, olivine-rich mantle, orthopyroxene-rich lower crust and basaltic upper crust. The igneous lithologies were subjected to post-crystallization thermal processing, and most eucrites show textural and mineral-compositional evidence for metamorphism. The cause of this common metamorphism is unclear, but may have resulted from rapid burial of early basalts by later flows caused by high effusion rates on Vesta. The observed surface of Vesta is covered by fragmental debris resulting from impacts, and most HEDs are brecciated. Many eucrites and diogenites are monomict breccias indicating a lack of mixing. However, many HEDs are polymict breccias. Howardites are the most thoroughly mixed polymict breccias, yet only some of them contain evidence for residence in the true regolith. Based on the numbers of meteorites, compositions of howardites, and models of magma ocean solidification, cumulate eucrites and their residual ferroan mafic melts are minor components of the vestan crust.

Reference
Mittlefehldt DW (2014) Asteroid (4) Vesta: I. The howardite-eucrite-diogenite (HED) clan of meteorites. Chemie der Erde (in Press)
Link to Article [doi:10.1016/j.chemer.2014.08.002]

Copyright Elsevier

^1,2János Kovacs,²István Sajó, ^3,4Zsuzsanna Márton, ^1,2Viktor Jáger, ⁵Tibor Hegedüs, ⁶Tibor Berecz, ⁴Tamás Tóth, ⁷Péter Gyenizse, ^1,2András Podobni
¹Department of Geology and Meteorology, University of Pécs, H-7624 Pécs, Ifjúság u. 6, Hungary
²Environmental Analytical and Geoanalytical Research Group, Szentágothai Research Centre, University of Pécs, H-7624 Pécs, Ifjúság u. 20, Hungary
³MTA-PTE High-Field Terahertz Research Group, H-7624, Pécs Ifjúság u. 6, Hungary
⁴Institute of Physics, University of Pécs, H-7624, Pécs Ifjúság u. 6, Hungary
⁵Baja Astronomical Observatory, H-6500 Baja, POB 766, Hungary
⁶Department of Materials Science and Engineering, Budapest University of Technology and Economics, H-1111 Budapest, Bertalan L. u. 7, Hungary
⁷Department of Cartography and Geoinformatics, University of Pécs, H-7624 Pécs, Ifjúság u. 6, Hungary

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Reference
Kovacs J, István Sajób, Márton Z, Jáger V, Hegedüs T, Berecz T, Tóth T, Gyenizse P, Podobni A (2014) Csátalja, the largest H4-5 chondrite from Hungary. Planetary and Space Science (in Press)
Link to Article [doi:10.1016/j.pss.2014.11.009]

¹M.C. De Sanctis, ¹A. Frigeri, ^1,2E. Ammannito, ¹F. Tosi, ^1,3S. Marchi, ¹F. Zambon, ⁴C.A. Raymond, ²C.T. Russell
¹INAF, Istituto di Astrofisica e Planetologia Spaziali, Area di Ricerca di Tor Vergata, 00133 Roma, Italy
²Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095, USA
³SSERVI Southwest Research Institute, 1050 Walnut St, Suite 300, Boulder, CO 80302
⁴Jet Propulsion Laboratory, Pasadena, CA 91109, USA

The young Marcia crater on Vesta displays several interesting features, including pitted and smooth terrains, exposure of relatively bright and dark material, and enrichments of hydrated material in the ejecta. Several questions arise about the origin of Marcia and of the dark material (exogenic material versus volcanic or impact melts) and the smooth and pitted terrains. Here we describe the results of the spectral and thermal analysis of the Marcia crater, with a particular effort to assess the composition of the different units, identifying the presence of OH and its correlation with dark material. Detailed studies of the Marcia crater wall, smooth and floor units reveal a compositional rich terrain with small areas enriched in diogenites with respect to the general eucritic regolith dominating the equatorial region of Vesta. The signature of OH is particularly clear in the pitted floor, dark material, smooth unit, and ejecta. The pitted terrains, beside their appearance, also show thermal anomalies, being colder with respect to the surrounding terrains. The presence of OH, concentrated in darker layers, and the pitted crater floor indicate that the area where the Marcia impact event occurred was rich in volatiles. The results show how the relatively young impact events have modified the surface of Vesta, disrupting a layer of dark material once present on Vesta’s equatorial terrain and exposing fresh, bright material rich in pyroxene.

Reference
De Sanctis MC, Frigeri A, Ammannito E, Tosi F, Marchi S, Zambon F, Raymond CA, Russell CT (2014) Mineralogy of Marcia, the youngest large crater of Vesta: Character and distribution of pyroxenes and hydrated material. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2014.10.051]

Copyright Elsevier

^1,2M. Cañada-Assandri, ^1,2R. Gil-Hutton, ³A.O. Ribeiro
¹Complejo Astrónmico El Leoncito (CONICET), Av. España 1512 sur, J5402DSP. San Juan, Argentina
²Universidad Nacional de San Juan, Av. Ignacio de la Roza 590 oeste, J5402DCS. San Juan, Argentina
³Observatorio Nacional, Rua General José Cristino 77, Rio de Janeiro, 20921-400, Brazil

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Reference
Cañada-Assandri M, Gil-Hutton R, Ribeiro AO (2014) The Hungaria population: A comparison between sub-Groups. Planetary and Space Science (in Press)
Link to Article [doi:10.1016/j.pss.2014.11.004]

^1,2,3Xiaoxia Duan,¹Marcel Regelous
¹GeoZentrum Nordbayern, Universität Erlangen-Nürnberg, Schloßgarten 5, 91054 Erlangen, Germany
²Institute of Geology and Geophysics, Chinese Academy of Sciences, 100029 Beijing, PR China
²University of Chinese Academy of Sciences, 100049 Beijing, PR China

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Reference
Duan X, Regelous M (2014) Rapid determination of 26 elements in iron meteorites using matrix removal and membrane desolvating quadrupole ICP-MS. Journal Analalytical Atomic Spectrometry 29, 2379-2387.
Link to Article [DOI:10.1039/C4JA00244J]

¹Rahat Khan, ¹Yuta Yokozuka, ¹Saki Terai, ¹Naoki Shirai, ¹Mitsuru Ebihara
¹Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Japan

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Reference
Khan R, Yokozuka Y, Terai S, Shirai N, Ebihara M (2014) Accurate determination of Zn in geological and cosmochemical rock samples by isotope dilution inductively coupled plasma mass spectrometry. Journal Analytical Atomic Spectrometry (in Press)
Link to Article [DOI: 10.1039/C4JA00344F]

¹J. Guignard, ²M.J. Toplis
¹European Synchrotron Radiaton Facility (ESRF), 71 Avenue des Martyrs, 38000, Grenoble
²Institut de Recherche en Astrophysique et Planétologie (UMR5277 CNRS/Université Paul Sabatier), Observatoire Midi-Pyrénées, 14, Av. E. Belin, 31400 Toulouse, France

The textural characteristics of opaque iron-rich phases (kamacite-taenite and troilite) have been quantified in the eight H-chondrites (two H4, three H5 and three H6) that have been the subject of previous thermo-chronological studies. These samples are of interest as they have temperature-time paths during cooling that have been shown to be consistent with radiogenic heating by 26Al on a single parent-body, thus offering the possibility to quantitatively link textural characteristics to thermal history. In addition to these eight samples, two other H5 samples (Forest City & Misshof) and two primitive achondrites (Acapulco & Lodran) were studied for comparison. The textural characteristics measured include: i) phase proportions, ii) the length of metal-sulphide contacts, iii) dihedral angle at contacts with silicate grains, iv) grain shape and circularity, v) grain size and size distributions. The absolute and relative proportions of metals and sulphides are found to be approximately constant in all studied H chondrites, consistent with evolution in a chemically closed system. With increasing degree of thermal metamorphism, H-chondrites are found to show evidence for separation of metal and sulphide phases, increasing grain circularity, increasing grain size, and modification of size distributions characterized by the elimination of small grains. Variations of these parameters are found to be almost identical for sulphides and metals suggesting similar growth mechanisms for these two phases. Furthermore, trends between samples place them consistently in the same order: Sainte Marguerite (H4), Forest Vale (H4), Nadiabondi (H5), Richardton (H5), Forest City (H5), Misshof (H5), Allegan (H5), Kernouvé (H6), Guareña (H6) and Estacado (H6). In all cases Acapulco and Lodran extend the trends observed among the H-chondrites. In general, it is found that characteristics requiring material transport over shorter length scales (i.e. within grains) show greater variation for low petrographic type (H4/H5) and reach textural equilibrium earlier in the sequence than characteristics which require transport over larger distances (i.e. between grains). In the latter case (e.g. slopes of crystal size distribution), variations are most marked for H6 samples, trends that are significantly extended by Acapulco and Lodran, highlighting the role of silicate melt on variations in textural properties. Crystal size distributions imply normal grain growth (NGG) for both metals and sulphides, possibly controlled by grain boundary migration of olivine and/or pyroxene. Comparison of these results with geochemically constrained thermal models of the H-chondrite parent body shows an excellent correlation between average crystal sizes, and inferred depths in the original parent body, consistent with expectations based on thermal modelling. This study highlights the potential of grain-size as a quantitative marker of the degree of thermal metamorphism, although further work on a wider set of samples will be required to explore the limits of this approach.

Reference
Guignard J, Toplis MJ (2014) Textural properties of iron-rich phases in H ordinary chondrites and quantitative links to the degree of thermal metamorphism. Geochimica et Cosmochimica Acta (in Press)

Link to Article: [DOI: 10.1016/j.gca.2014.11.006]

Copyright Elsevier

¹D.S.Lauretta et al. (>10)*
¹Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
*Find the extensive, full author and affiliation list on the publishers website

We review the results of an extensive campaign to determine the physical, geological, and dynamical properties of asteroid (101955) Bennu. This investigation provides information on the orbit, shape, mass, rotation state, radar response, photometric, spectroscopic, thermal, regolith, and environmental properties of Bennu. We combine these data with cosmochemical and dynamical models to develop a hypothetical timeline for Bennu’s formation and evolution. We infer that Bennu is an ancient object that has witnessed over 4.5 Gyr of solar system history. Its chemistry and mineralogy were established within the first 10 Myr of the solar system. It likely originated as a discrete asteroid in the inner Main Belt approximately 0.7–2 Gyr ago as a fragment from the catastrophic disruption of a large (approximately 100-km), carbonaceous asteroid. It was delivered to near-Earth space via a combination of Yarkovsky-induced drift and interaction with giant-planet resonances. During its journey, YORP processes and planetary close encounters modified Bennu’s spin state, potentially reshaping and resurfacing the asteroid. We also review work on Bennu’s future dynamical evolution and constrain its ultimate fate. It is one of the most Potentially Hazardous Asteroids with an approximately 1-in-2700 chance of impacting the Earth in the late 22nd century. It will most likely end its dynamical life by falling into the Sun. The highest probability for a planetary impact is with Venus, followed by the Earth. There is a chance that Bennu will be ejected from the inner solar system after a close encounter with Jupiter. OSIRIS-REx will return samples from the surface of this intriguing asteroid in September 2023.

Reference
Lauretta DS et al. (2014) The OSIRIS-REx target asteroid (101955) Bennu: Constraints on its physical, geological, and dynamical nature from astronomical observations. Meteoritics and Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12353]

Published by arrangement with John Wiley & Sons 

^1,2,3Jemma Davidson et al. (>10)*
¹Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
²Planetary and Space Sciences, The Open University, Milton Keynes, Buckinghamshire, UK
³Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, District of Columbia, USA
*Find the extensive, full author and affiliation list on the publishers website

Here, we report the mineralogy, petrography, C-N-O-stable isotope compositions, degree of disorder of organic matter, and abundances of presolar components of the chondrite Roberts Massif (RBT) 04133 using a coordinated, multitechnique approach. The results of this study are inconsistent with its initial classification as a Renazzo-like carbonaceous chondrite, and strongly support RBT 04133 being a brecciated, reduced petrologic type >3.3 Vigarano-like carbonaceous (CV) chondrite. RBT 04133 shows no evidence for aqueous alteration. However, it is mildly thermally altered (up to approximately 440 °C); which is apparent in its whole-rock C and N isotopic compositions, the degree of disorder of C in insoluble organic matter, low presolar grain abundances, minor element compositions of Fe,Ni metal, chromite compositions and morphologies, and the presence of unequilibrated silicates. Sulfides within type I chondrules from RBT 04133 appear to be pre-accretionary (i.e., did not form via aqueous alteration), providing further evidence that some sulfide minerals formed prior to accretion of the CV chondrite parent body. The thin section studied contains two reduced CV3 lithologies, one of which appears to be more thermally metamorphosed, indicating that RBT 04133, like several other CV chondrites, is a breccia and thus experienced impact processing. Linear foliation of chondrules was not observed implying that RBT 04133 did not experience high velocity impacts that could lead to extensive thermal metamorphism. Presolar silicates are still present in RBT 04133, although presolar SiC grain abundances are very low, indicating that the progressive destruction or modification of presolar SiC grains begins before presolar silicate grains are completely unidentifiable.

Reference
Davidson J et al. (2014) Petrography, stable isotope compositions, microRaman spectroscopy, and presolar components of Roberts Massif 04133: A reduced CV3 carbonaceous chondrite. Meteoritics & Planetary Society (in Press)
Link to Article [DOI: 10.1111/maps.12377]

Published by Arrangement with John Wiley & Sons