^1,2Melissa A. Morris, ³Laurence A. J. Garvie, ²L. Paul Knauth
¹State University of New York, Cortland, NY 13045, USA
²School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA
³Center for Meteorite Studies, Arizona State University, Tempe, AZ 85287, USA

Many aspects of planet formation are controlled by the amount of gas remaining in the natal protoplanetary disks (PPDs). Infrared observations show that PPDs undergo a transition stage at several megayears, during which gas densities are reduced. Our Solar System would have experienced such a stage. However, there is currently no data that provides insight into this crucial time in our PPD’s evolution. We show that the Isheyevo meteorite contains the first definitive evidence for a transition disk stage in our Solar System. Isheyevo belongs to a class of metal-rich meteorites whose components have been dated at almost 5 Myr after formation of Ca, Al-rich inclusions, and exhibits unique sedimentary layers that imply formation through gentle sedimentation. We show that such layering can occur via the gentle sweep-up of material found in the impact plume resulting from the collision of two planetesimals. Such sweep-up requires gas densities consistent with observed transition disks (10−12–10−11 g cm−3). As such, Isheyevo presents the first evidence of our own transition disk and provides new constraints on the evolution of our solar nebula.

Reference
Morris MA, Garvie LAJ, Knauth LP (2015) New Insight into the Solar System’s Transition Disk Phase Provided by the Metal-rich Carbonaceous Chondrite Isheyevo. Astrophysical Journal 801 L22.
Link to Article [doi:10.1088/2041-8205/801/2/L22]

¹Daniel Ozdín et al. (>10)*
¹Department of Mineralogy and Petrology, Faculty of Natural Sciences, Comenius University, Bratislava, Slovak Republic
*Find the extensive, full author and affiliation list on the publishers website

The Košice meteorite was observed to fall on 28 February 2010 at 23:25 UT near the city of Košice in eastern Slovakia and its mineralogy, petrology, and geochemistry are described. The characteristic features of the meteorite fragments are fan-like, mosaic, lamellar, and granular chondrules, which were up to 1.2 mm in diameter. The fusion crust has a black-gray color with a thickness up to 0.6 mm. The matrix of the meteorite is formed mainly by forsterite (Fo80.6); diopside; enstatite (Fs16.7); albite; troilite; Fe-Ni metals such as iron and taenite; and some augite, chlorapatite, merrillite, chromite, and tetrataenite. Plagioclase-like glass was also identified. Relative uniform chemical composition of basic silicates, partially brecciated textures, as well as skeletal taenite crystals into troilite veinlets suggest monomict breccia formed at conditions of rapid cooling. The Košice meteorite is classified as ordinary chondrite of the H5 type which has been slightly weathered, and only short veinlets of Fe hydroxides are present. The textural relationships indicate an S3 degree of shock metamorphism and W0 weathering grade. Some fragments of the meteorite Košice are formed by monomict breccia of the petrological type H5. On the basis of REE content, we suggest the Košice chondrite is probably from the same parent body as H5 chondrite Morávka from Czech Republic. Electron-microprobe analysis (EMPA) with focused and defocused electron beam, whole-rock analysis (WRA), inductively coupled plasma mass and optical emission spectroscopy (ICP MS, ICP OES), and calibration-free laser induced breakdown spectroscopy (CF-LIBS) were used to characterize the Košice fragments. The results provide further evidence that whole-rock analysis gives the most accurate analyses, but this method is completely destructive. Two other proposed methods are partially destructive (EMPA) or nondestructive (CF-LIBS), but only major and minor elements can be evaluated due to the significantly lower sample consumption.

Reference
Ozdín D et al. (2015) Mineralogy, petrography, geochemistry, and classification of the Košice Meteorite. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12405]

Published by arrangement with John Wiley&Sons

The most popular papers in Cosmochemistry Papers in March were:

1-Krzesińska A, Gattacceca J, Friedrich JM and Rochette P (2015) Impact-related noncoaxial deformation in the Pułtusk H chondrite inferred from petrofabric analysis. Meteoritics & Planetary Sciences (in Press) Link to Article [doi:10.1111/maps.12429]

2-Van Hoesel A, Hoek WZ, Pennock GM, Kaiser K, Plümper O, Jankowski M, Hamers MF, Schlaak N, Küster M, Andronikov AV and Drury MR (2015) A search for shocked quartz grains in the Allerød-Younger Dryas boundary layer. Meteoritics & Planetary Sciences (in Press) Link to Article [doi:10.1111/maps.12435]

3-Charnoz S, Aleon J, Chaumard N, Baillie K, Taillifet E (2015) Growth of calcium-aluminum-rich inclusions by coagulation and fragmentation in a turbulent protoplanetary disk: observations and simulations. Icarus (in Press) Link to Article [doi:10.1016/j.icarus.2015.01.023]

4-Peplowski PN et al. (2015) Geochemical terranes of Mercury’s northern hemisphere as revealed by MESSENGER neutron measurements. Icarus (in Press) Link to Article [doi:10.1016/j.icarus.2015.02.002]

5-Hopkins MD, Mojzsis SJ (2015) A protracted timeline for lunar bombardment from mineral chemistry, Ti thermometry and U–Pb geochronology of Apollo 14 melt breccia zircons. Contributions to Mineralogy and Petrology 169:30 Link to Article [DOI 10.1007/s00410-015-1123-x]

5-Greenberger RN, Mustard JF, Cloutis EA, Pratt LM, Sauer PE, Mann P, Turner K, Dyar MD, Bish DL (2015) Serpentinization, iron oxidation, and aqueous conditions in an ophiolite: Implications for hydrogen production and habitability on Mars. Earth and Planetary Science Letters 416, 21–34 Link to Article [doi:10.1016/j.epsl.2015.02.002]

¹Stein B. Jacobsen
¹Gang Yu
¹Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA

Heterogeneities in terrestrial samples for 182W/183W and 142Nd/144Nd are only preserved in Hadean and Archean rocks while heterogeneities in 129Xe/130Xe and 136Xe/130Xe persist to very young mantle-derived rocks. In contrast, meteorites from Mars show that the Martian mantle preserves heterogeneities in 182W/183W and 142Nd/144Nd up to the present. As a consequence of the probable “deep magma ocean” core formation process, we assume that the Earth and Mars both had a very early two-mantle-reservoir structure with different initial extinct nuclide isotopic compositions (different 182W/183W, 142Nd/144Nd, 129Xe/130Xe, 136Xe/130Xe ratios). Based on this assumption, we developed a simple stochastic model to trace the evolution of a mantle with two initially distinct layers for the extinct isotopes and its development into a heterogeneous mantle by convective mixing and stretching of these two layers. Using the extinct isotope system 182Hf-182W, we find that the mantles of Earth and Mars exhibit substantially different mixing or stirring rates. This is consistent with Mars having cooled faster than the Earth due to its smaller size, resulting in less efficient mantle mixing for Mars. Moreover, the mantle stirring rate obtained for Earth using 182Hf-182W is consistent with the mantle stirring rate of ~500 Myr constrained by the long-lived isotope system, 87Rb-87Sr and 147Sm-143Nd. The apparent absence of 182W/183W isotopic heterogeneity in modern terrestrial rocks is attributed to very active mantle stirring which reduced the 182W/183W isotopic heterogeneity to a relatively small scale (~83 m for a mantle stirring rate of 500 Myr) compared to the common sampling scale of terrestrial basalts (~30 or 100 km). Our results also support the “deep magma ocean” core formation model as being applicable to both Mars and Earth.

Reference
Jacobsen SB, Yu G (2015) Extinct isotope heterogeneities in the mantles of Earth and Mars: Implications for mantle stirring rates. Meteoritics&Planetary Sciences (in Press)
Link to Article [DOI: 10.1111/maps.12426]

Published by arrangement with John Wiley & Sons

¹J.A. Barrat,²O. Rouxel,³K. Wang,^4,5F. Moynier,^6,7A. Yamaguchi,⁸A. Bischoff,⁹J. Langlade
¹Université de Bretagne Occidentale, Institut Universitaire Européen de la Mer, CNRS UMR 6538, Place Nicolas Copernic, 29280 Plouzané, France
²IFREMER, centre de Brest, 29280 Plouzané, France
³Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, USA
⁴Institut de Physique du Globe de Paris, Institut Universitaire de France, Université Paris Diderot, Sorbonne Paris Cité, 1 rue Jussieu, 75238 Paris Cedex 05, France
⁵Institut Universitaire de France, Paris, France
⁶National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan
⁷Department of Polar Science, School of Multidisciplinary Science, Graduate University for Advanced Sciences, Tachikawa, Tokyo 190-8518, Japan
⁸Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
⁹CNRS UMS 3113, I.U.E.M., Place Nicolas Copernic, 29280 Plouzané Cedex, France

Ureilite meteorites are achondrites that are debris of the mantle of a now disrupted differentiated asteroid rich in carbon. They provide a unique opportunity to study the differentiation processes of such a body. We analyzed the iron isotopic compositions of 30 samples from the Ureilite Parent Body (UPB) including 29 unbrecciated ureilites and one ureilitic trachyandesite (ALM-A) which is at present the sole large crustal sample of the UPB. The δ56Fe of the whole rocks fall within a restricted range, from 0.01 to 0.11‰, with an average of +0.056±0.008‰+0.056±0.008‰, which is significantly higher than that of chondrites. We show that this difference can be ascribed to the segregation of S-rich metallic melts at low degrees of melting at a temperature close to the Fe–FeS eutectic, and certainly before the onset of the melting of the silicates (View the MathML source<1100°C), in agreement with the marked S depletions, and the siderophile element abundances of the ureilites. These results point to an efficient segregation of S-rich metallic melts during the differentiation of small terrestrial bodies.

Reference
Barrat JA, Rouxel O,Wang K, Moynier F,Yamaguchi A,Bischoff A, Langlade J (2015) Early stages of core segregation recorded by Fe isotopes in an asteroidal mantle. Earth and Planetary Science Letters, 419, 93–100
Link to Article [http://dx.doi.org/10.1016/j.epsl.2015.03.026]

Copyright Elsevier

¹Thomas B. McCord,²Jennifer E.C. Scully
¹The Bear Fight Institute, Winthrop WA 98862
²Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, 595 Charles Young Drive East, Box 951567, Los Angeles, CA 90095-1567

Vesta’s surface composition has been of special interest since early, disk-integrated telescopic spectral observations indicated that it is basaltic, differentiated and similar to the HED (howardite-eucrite-diogenite) class of meteorites. The Dawn mission, orbiting Vesta, provided a large and varied set of unique observations on the detailed mineralogy, molecular and elemental composition, and their distributions in association with surface features and geology. The set of articles contained in this special issue is the first treatment of the entire surface composition of Vesta using the complete Dawn Vesta data set and the calibrations from the entire campaign. Most articles treat a region of Vesta within the context of the entire body, but there are several articles that treat global or technical topics. As a whole, these articles provide a current and comprehensive view of Vesta’s composition using all the relevant data that is available. Vesta’s surface composition is consistent with the upper layer being created by igneous processes, while a more mafic lithology generally associated with a mantle is surprisingly limited. There is evidence of contamination by low velocity infall of several types of objects: dark hydrated/hydroxolated material, and probably Fe/Mg silicates differing from Vesta’s. Isolated blocks of differing compositions, seen especially in crater walls, could indicate incomplete melting and mixing during the differentiation process, and retention of some evidence of the original building blocks of the accreted Vesta. This lead article introduces and provides the context for the following articles, presents a summary of the various findings, and integrates them into overall conclusions.

Reference
McCord TB, Scully JEC (2015) The Composition of Vesta from the Dawn Mission. Geochimica et Cosmochimica Acta (in Press)
Link to Article [http://dx.doi.org/10.1016/j.icarus.2015.03.022]

Copyright Elsevier

¹Timothy J. McCoy,²Andrew W. Beck,³Thomas H. Prettyman,⁴David W. Mittlefehldt
¹Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560-0119, USA
²Applied Physics Laboratory, The Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, MD 20723, USA
³Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719, USA
⁴Astromaterials Research Office, NASA Johnson Space Center, Mail code KR, Houston, TX 77058, USA

More than 200 years after its discovery, asteroid (4) Vesta is thought to be the parent body for the howardite, eucrite and diogenite (HED) meteorites. The Dawn spacecraft spent ∼14 months in orbit around this largest, intact differentiated asteroid to study its internal structure, geology, mineralogy and chemistry. Carrying a suite of instruments that included two framing cameras, a visible-near infrared spectrometer, and a gamma-ray and neutron detector, coupled with radio tracking for gravity, Dawn revealed a geologically and geochemically complex world. A constrained core size of ∼110–130 km radius is consistent with predictions based on differentiation models for the HED meteorite parent body. Hubble Space Telescope observations had already shown that Vesta is scarred by a south polar basin comparable in diameter to that of the asteroid itself. Dawn showed that the south polar Rheasilvia basin dominates the asteroid, with a central uplift that rivals the large shield volcanoes of the Solar System in height. An older basin, Veneneia, partially underlies Rheasilvia. A series of graben-like equatorial and northern troughs were created during these massive impact events 1–2 Ga ago. These events also resurfaced much of the southern hemisphere and exposed deeper-seated diogenitic lithologies. Although the mineralogy and geochemistry vary across the surface for rock-forming elements and minerals, the range is small, suggesting that impact processes have efficiently homogenized the surface of Vesta at scales observed by the instruments on the Dawn spacecraft. The distribution of hydrogen is correlated with surface age, which likely results from the admixture of exogenic carbonaceous chondrites with Vesta’s basaltic surface. Clasts of such material are observed within the surficial howardite meteorites in our collections. Dawn significantly strengthened the link between (4) Vesta and the HED meteorites, but the pervasive mixing, lack of a convincing and widespread detection of olivine, and poorly-constrained lateral and vertical extents of units leaves unanswered the central question of whether Vesta once had a magma ocean. Dawn is continuing its mission to the presumed ice-rich asteroid (1) Ceres.

Reference
McCoy TJ, Beck AW, Prettyman TH, Mittlefehldt DW (2015) Asteroid (4) Vesta II: Exploring a geologically and geochemically complex world with the Dawn Mission. Chemie der Erde (in Press)
Link to Article [http://dx.doi.org/10.1016/j.chemer.2014.12.001]

Copyright Elsevier

¹Yamamoto S. et al.(>10)*
¹Center for Environmental Measurement and Analysis, National Institute for Environmental Studies, Tsukuba, Japan
*Find the extensive, full author and affiliation list on the publishers website

We present details of the global distribution of high-Ca pyroxene (HCP)-rich sites in the lunar highlands based on the global dataset of hyper-spectral reflectance obtained by the SELENE Spectral Profiler. Most HCP-rich sites in the lunar highlands are found at fresh impact craters. In each crater, most of the detection points are distributed on the ejecta, rim, and floor of the impact craters rather than the central peaks, while the central peaks are dominated by purest anorthosite (PAN). This indicates that HCP-rich materials originate from relatively shallower regions of the lunar crust than PAN. In addition, while all ray craters with sizes larger than ~40km possess HCP-rich materials, small fresh craters with sizes less than ~6−−10km do not, indicating that the uppermost mixing layers in the lunar crust are not dominated by HCP. Based on these results, we propose that in the upper lunar crust, a HCP-rich zone overlying the PAN layer exists below the uppermost mixing layer. This HCP-rich zone may originate from interstitial melt during the formation of the flotation anorthositic cumulate, while an impact ejecta origin, impact melt origin, and/or magmatic intrusion into the upper lunar crust may also account for the occurrence of HCP-rich sites in the highlands.

Reference
Yamamoto S et al. (2015) Global occurrence trend of high-Ca pyroxene on lunar highlands and its implications. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004740]

Published by arrangement with John Wiley&Sons

^1,2E.C. Sklute, ¹H.B.Jensen, ¹A.D. Rogers, ¹R.J.
Reeder
¹Stony Brook University, Department of Geosciences, Stony Brook, NY 11794-2100, USA
²Mount Holyoke College, Department of Astronomy, South Hadley, MA

Current or past brine hydrologic activity on Mars may provide suitable conditions for the formation of amorphous ferric sulfates. Once formed, these phases would likely be stable under current Martian conditions, particularly at low- to mid-latitudes. Therefore, we consider amorphous iron sulfates (AIS) as possible components of Martian surface materials. Laboratory AIS were created through multiple synthesis routes, and characterized with total x-ray scattering, thermogravimetric analysis, scanning electron microscopy, visible/near-infrared (VNIR), thermal infrared (TIR), and Mössbauer techniques. We synthesized amorphous ferric sulfates (Fe(III)2(SO4)3•~6-8H2O) from sulfate-saturated fluids via vacuum dehydration or exposure to low relative humidity (<11%). Amorphous ferrous sulfate (Fe(II)SO4•~1H2O) was synthesized via vacuum dehydration of melanterite. All AIS lack structural order beyond 11 Å. The short-range (<5 Å) structural characteristics of amorphous ferric sulfates resemble all crystalline reference compounds; structural characteristics for the amorphous ferrous sulfate are similar to but distinct from both rozenite and szomolnokite. VNIR and TIR spectral data for all AIS display broad, muted features consistent with structural disorder and are spectrally distinct from all crystalline sulfates considered for comparison. Mössbauer spectra are also distinct from crystalline phase spectra available for comparison. AIS should be distinguishable from crystalline sulfates based on the position of their Fe-related absorptions in the visible range and their spectral characteristics in the TIR. In the NIR, bands associated with hydration at ~1.4 and 1.9 µm are significantly broadened, which greatly reduces their detectability in soil mixtures. AIS may contribute to the amorphous fraction of soils measured by the Curiosity rover.

Reference
Sklute EC, Jensen HB, Rogers AD, Reeder RJ (2015) Morphological, Structural, and Spectral Characteristics of Amorphous Iron Sulfates. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004784]

Published by arrangement with John Wiley&Sons

¹Steven J. Jaret, ¹William R. Woerner, ¹Brian L. Phillips, ^2,3Lars Ehm¹Hanna Nekvasil, ^4,5Shawn P. Wright, ¹TimothyD.Glotch
¹Department of Geosciences, State University of New York at Stony Brook, Stony Brook, New York, USA,
²Mineral Physics Institute, State University of New York at Stony Brook, Stony Brook, New York, USA,
³Photon Sciences Directorate, Brookhaven National Laboratory, Upton, New York, USA,
⁴Department of Geosciences, Auburn University, Auburn, Alabama, USA,
⁵Planetary Science Institute, Tucson, Arizona, USA

We present the results of a combined study of shocked labradorite from the Lonar crater, India, using optical microscopy, micro-Raman spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, high-energy X-ray total scattering experiments, and micro-Fourier transform infrared (micro-FTIR) spectroscopy. We show that maskelynite of shock class 2 is structurally more similar to fused glass than to crystalline plagioclase. However, there are slight but significant differences—preservation of original preimpact igneous zoning, anisotropy at infrared wavelengths, X-ray anisotropy, and preservation of some intermediate range order—which are all consistent with a solid-state transformation from plagioclase to maskelynite.

Jaret SJ, Woerner WR, Phillips BL, Ehm L, Nekvasil H, Wright SP, Glotch TD (2015) Maskelynite formation via solid-state transformation: Evidence of infrared and X-ray anisotropy. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004764]

Published by arrangement with John Wiley&Sons