bluuebunny/crossref_metadata_2025 huggingface dataset:
Smelting of Fe‐bearing glass during hypervelocity capture in aerogel
Authors: Marcus Matthew A. , Fakra Sirine , Westphal Andrew J. , Snead Christopher J. , Keller Lindsay P. , Kearsley Anton , Burchell Mark J.
Published: January 2010

Abstract— Hypervelocity capture of material in aerogel can expose particles to high transient temperatures. We tested some of the possible effects of capture by using a light‐gas gun to shoot particles of basalt glass into aerogel at 6.1 km s−1. Using synchrotron‐based micro‐X‐ray absorption spectroscopy (μXAS), we find that the starting material, in which the Fe was trivalent, is chemically reduced to divalent. In addition, some fragments were chemically reduced so that they contained Fe0 in a form spectroscopically consistent with a mixture of two forms of iron carbide (cohenite and haxonite). The carbon presumably originated from organic impurities in the aerogel. High‐resolution transmission electron microscopy (HRTEM) imaging shows the presence of Fe‐rich crystalline nanoparticles. A similar species has been found in actual Stardust material, suggesting that “smelting” effects occurred during capture and should be taken into account when interpreting data on Stardust samples.
Recovering the elemental composition of comet Wild 2 dust in five Stardust impact tracks and terminal particles in aerogel
Authors: Ishii Hope A. , Brennan Sean , Bradley John P. , Luening Katharina , Ignatyev Konstantin , Pianetta Piero
Published: January 2010

Abstract— The elemental (non‐volatile) composition of five Stardust impact tracks and terminal particles left from capture of comet 81P/Wild 2 dust were mapped in a synchrotron X‐ray scanning microprobe with full fluorescence spectra at each pixel. Because aerogel includes background levels of several elements of interest, we employ a novel “dual threshold” approach to discriminate against background contaminants: an upper threshold, above which a spectrum contains cometary material plus aerogel and a lower threshold below which it contains only aerogel. The difference between normalized cometary‐plus‐background and background‐only spectra is attributable to cometary material. The few spectra in‐between are discarded since misallocation is detrimental: cometary material incorrectly placed in the background spectrum is later subtracted from the cometary spectrum, doubling the loss of reportable cometary material. This approach improves accuracy of composition quantification. We present the refined whole impact track and terminal particle elemental abundances for the five impact tracks. One track shows mass increases in Cr and Mn (1.4×), Cu, As and K (2×), Zn (4×), and total mass (13%) by dual thresholds compared to a single threshold. Major elements Fe and Ni are not significantly affected. The additional Cr arises from cometary material containing little Fe. We exclude Au intermixed with cometary material because it is found to be a localized surface contaminant carried by comet dust into an impact track. The dual threshold technique can be used in other situations where elements of interest in a small sample embedded in a matrix are also present in the matrix itself.
TOF‐SIMS analysis of cometary particles extracted from Stardust aerogel
Authors: Stephan Thomas , Flynn George J. , Sandford Scott A. , Zolensky Michael E.
Published: January 2010

Abstract—Sections of seven cometary fragments extracted from the aerogel collector flown on the Stardust mission to comet 81P/Wild 2 were investigated with TOF‐SIMS. These grains showed a rather heterogeneous chemical and mineralogical composition on a submicrometer scale. However, their average chemical composition is close to bulk CI chondritic values, which is consistent with analyses of numerous Stardust samples using various techniques. As a result, the TOF‐SIMS analyses support the conclusion that Wild 2 has a CI‐like bulk composition. The cometary particles resemble anhydrous chondritic porous interplanetary dust particles, which have previously been suggested to originate from comets. For one of the fragments, polycyclic aromatic hydrocarbons that could possibly be attributed to the comet were observed.
Carbon investigation of two Stardust particles: A TEM, NanoSIMS, and XANES study
Authors: Matrajt G. , Ito M. , Wirick S. , Messenger S. , Brownlee D. E. , Joswiak D. , Flynn G. , Sandford S. , Snead C. , Westphal A.
Published: January 2010

Abstract— In this work we present the results of a systematic search for cometary organics in 14 Stardust particles (particles from comet 81P/Wild 2, captured by NASA's Stardust mission) by TEM and multidisciplinary studies (XANES and NanoSIMS) of Febo and Ada, two of the organic‐ bearing particles identified. The combination of the three analytical techniques has established the presence of organic, cometary C in both particles. Using energy‐filtered and high‐resolution imaging it was shown that the C is amorphous and rare, given that it is found in grains ≤200 nm in size that are not abundant throughout the particles. The XANES maps and spectra of the carbonaceous areas identified with the TEM have shown that the carbonaceous material is organic due to the presence of carbonyl (C=O) functional groups and the overlapping of C and N on the same grains. In addition, several different C‐XANES spectra were obtained from the same particle, suggesting that there is diversity in the types of carbonaceous phases present in these particles, as well as a heterogeneous distribution of the carbonaceous phases within these particles. The C‐XANES spectra obtained are different from C‐XANES spectra of carbonaceous chondrites and IDPs. In the particle Febo we found five spots showing a pronounced enrichment in the isotope 15N (δ15N from 420 to 639 ± 20 to 70‰, 1s̀) that were clearly associated with the C‐rich regions. The carbonaceous material has approximately solar C and D/H isotopic compositions, and the bulk O isotopic composition was found to be s̀17 O = −18 ± 13‰ and δ18 O = −37 ± 12‰ (1s̀). In the particle Ada we found a C‐rich phase with enrichments in the isotope 15N (δ15 N = 550 ± 70 ‰, 1s̀) and the isotope D (δD = 610 ± 254‰, 1s̀). The C isotopic composition at this phase is solar (δ13 C = −4 ± 29‰, 1s̀). The bulk O isotopic composition of Ada was found to be δ17 O = 9 ± 14.6‰ and δ18 O = −7.3 ± 8.1‰ (2s̀).
Quantitative organic and light‐element analysis of comet 81P/Wild 2 particles using C‐, N‐, and O‐μ‐XANES
Authors: Cody George D. , Ade Harald , Alexander M. O'D. , Araki Tohru , Butterworth Anna , Fleckenstein Holger , Flynn George , Gilles Mary K. , Jacobsen Chris , Kilcoyne A. L. D. , Messenger Keiko , Sandford Scott A. , Tyliszczak Tolek , Westphal Andrew J. , Wirick Susan , Yabuta Hikaru
Published: January 2010

Abstract— Synchrotron‐based soft X‐ray micro‐analysis was performed on particles extracted from the Stardust aerogel collector in order to obtain detailed organic functional group information on any organic solids captured as part of the Principal Examination suite of analyses for samples from comet 81P/Wild 2. It is observed that cometary organic carbon captured in aerogel is present in a number of different manifestations and often intimately associated with silicates. Carbon X‐ray absorption near edge structure (XANES) spectra reveal considerable chemical complexity in all of the organic particles studied so far. Universally, the comet 81P/Wild 2 organic particles contain low concentrations of aromatic and/or olefinic carbon relative to aliphatic and heteroatom‐containing functional groups, e.g., amide, carboxyl, and alcohol/ethers. N‐XANES confirms the presence and assignments of these functional groups. In general, the XANES data record considerable chemical complexity across the range of organic samples currently analyzed. The atomic ratios, N/C and O/C, derived from XANES data reveal a wide range in heteroatom content; in all cases these elemental ratios are higher than that of primitive meteoritic organic matter. The wide range in chemistry, both in elemental abundances and specific organic functional groups, suggests that the comet 81P/Wild 2 organic solids may have multiple origins.
Characterization of the 1.2 μm M1 pyroxene band: Extracting cooling history from near‐IR spectra of pyroxenes and pyroxene‐dominated rocks
Authors: KLIMA Rachel L. , PIETERS Carlé M. , DYAR M. Darby
Published: January 2010

Abstract— The 1.2 μm band in near‐infrared spectra of pyroxenes results from Fe2+in the M1 crystallographic site. The distribution of Fe and Mg between the M1 and M2 sites is in part a function of the cooling rate and thermal history of a pyroxene. Combining near‐infrared and Mössbauer spectra for a series of compositionally controlled synthetic Mg, Fe, Ca pyroxenes, we quantify the strength of the 1.2 μm band as a function of Fe2+in the M1 site. Near‐infrared spectra are deconvolved into component absorptions that can be assigned to the M1 and M2 sites using the modified Gaussian model. The relative strength of the 1.2 μm band is shown to be directly related to the amount of Fe2+in the M1 site measured by Mössbauer spectroscopy. The strength of the 1.2 μm band relative to the combined strengths of the 1.2 and 2 μm bands, or the M1 intensity ratio, is calculated for 51 howardite, eucrite, and diogenite (HED) meteorites. Diogenites and cumulate eucrites exhibit the lowest M1 intensity ratios, consistent with their formation as slowly cooled cumulates. Basaltic eucrites exhibit a large range of M1 intensity ratios, all of which are consistently higher than the diogenites and cumulate eucrites. This example illustrates how the M1 intensity ratio can be a used as a tool for characterizing the cooling history of remotely detected pyroxene‐dominated rocks.
Polygonal impact craters in Argyre region, Mars: Implications for geology and cratering mechanics
Authors: ÖHMAN T. , AITTOLA M. , KOSTAMA V.‐P. , RAITALA J. , KORTENIEMI J.
Published: January 2010

Abstract— Impact craters are not always circular; sometimes their rims are composed of several straight segments. Such polygonal impact craters (PICs) are controlled by pre‐existing target structures, mainly faults or other similar planes of weakness. In the Argyre region, Mars, PICs comprise ˜ 17% of the total impact crater population (>7 km in diameter), and PICs are relatively more common in older geologic units. Their formation is mainly controlled by radial fractures induced by the Argyre and Ladon impact basins, and to a lesser extent by the basin‐concentric fractures. Also basin‐induced conjugate shear fractures may play a role. Unlike the PICs, ridges and graben in the Argyre region are mostly controlled by Tharsis‐induced tectonism, with the ridges being concentric and graben radial to Tharsis. Therefore, the PICs primarily reflect an old impact basin‐centered tectonic pattern, whereas Tharsis‐centered tectonism responsible for the graben and the ridges has only minor influence on the PIC rim orientations.

According to current models of PIC formation, complex PICs should form through a different mechanism than simple PICs, leading to different orientations of straight rim segments. However, when simple and complex PICs from same areas are studied, no statistically significant difference can be observed. Hence, in addition to enhanced excavation parallel to the strike of fractures (simple craters) and slumping along the fracture planes (complex craters), we propose a third mechanism involving thrusting along the fracture planes. This model is applicable to both simple and small complex craters in targets with some dominating orientations of structural weakness.
Differentiation and emplacement of the Worthington Offset Dike of the Sudbury impact structure, Ontario
Authors: HECHT L. , WITTEK A. , RILLER U. , MOHR T. , SCHMITT R. T. , GRIEVE R. A. F.
Published: January 2010

Abstract— The Offset Dikes of the 1.85 Ga Sudbury Igneous Complex (SIC) constitute a key topic in understanding the chemical evolution of the impact melt, its mineralization, and the interplay between melt migration and impact‐induced deformation. The origin of the melt rocks in Offset Dikes as well as mode and timing of their emplacement are still a matter of debate. Like many other offset dikes, the Worthington is composed of an early emplaced texturally rather homogeneous quartz‐diorite (QD) phase at the dike margin, and an inclusion‐ and sulfide‐rich quartz‐diorite (IQD) phase emplaced later and mostly in the centre of the dike. The chemical heterogeneity within and between QD and IQD is mainly attributed to variable assimilation of host rocks at the base of the SIC, prior to emplacement of the melt into the dike. Petrological data suggest that the parental magma of the Worthington Dike mainly developed during the pre‐liquidus temperature interval of the thermal evolution of the impact melt sheet (>1200 °C). Based on thermal models of the cooling history of the SIC, the two‐stage emplacement of the Worthington Dike occurred likely thousands to about ten thousand years after impact. Structural analysis indicates that an alignment of minerals and host rock fragments within the Worthington Dike was caused by ductile deformation under greenschist‐facies metamorphic conditions rather than flow during melt emplacement. It is concluded that the Worthington Offset Dike resulted from crater floor fracturing, possibly driven by late‐stage isostatic readjustment of crust underlying the impact structure.
Harvey Nininger's 1948 attempt to nationalize Meteor Crater
Authors: PLOTKIN Howard , Clarke Roy S.
Published: January 2010

Abstract— Harvey Nininger successfully petitioned the American Astronomical Society to pass a motion in support of nationalizing Meteor Crater, Arizona, at its June 1948 meeting. He alleged that the Barringer family, who held title to the crater, was depriving American citizens of its scenic beauty and scientific value. He then reportedly went on to make the unauthorized‐and false‐claim that the family would be receptive to a fair purchase offer for the crater. The Barringers, who had not been given advance warning of the petition and were not present at the meeting, felt ambushed. They quickly and forcefully rebutted Nininger's allegations, made it clear they had no intention of relinquishing their title to the crater, and terminated his exploration rights.

What led Nininger to such a curious and self‐defeating act? Based on our reading of his voluminous personal correspondence, we conclude that it was rooted primarily in his complex relationship with Frederick Leonard and Lincoln LaPaz, and his desire to establish a national institute for meteoritical research‐with them, originally, but after a serious falling out, on his own. Prevented from moving his American Meteorite Museum to the crater rim, Nininger wondered what would happen if the crater was nationalized and made into a public park, with an accompanying tourist center and museum. With characteristic élan, he could picture himself at its head, with a secure salary and adequate space to exhibit his meteorite collection.
Petrology and mineralogy of the angrite Northwest Africa 1670
Authors: JAMBON A. , BOUDOUMA O. , FONTEILLES M. , GUILLOU C. Le , BADIA D. , BARRAT J.‐A.
Published: January 2010

Abstract— Northwest Africa (NWA) 1670, contains olivines of up to 5 mm in size representing about 30% of the studied section. With subordinate clinopyroxene and chrome‐spinel microphenocrysts (0.2‐0.5 mm), they represent a xenocrystic association. Phenocrysts are surrounded by a groundmass, predominantly comprising bundles of plagioclase and clinopyroxene (typically 20 × 200 μm crystals). Olivine and kirschsteinite are present in the groundmass in lesser amounts. The olivine xenocrysts (Fo90) are significantly fractured and show mosaicism for their major part, the remaining showing faint undulatory extinction. They are surrounded with a rim of 100–200 μm zoned down to Fo80 and overgrown with serrated olivine, Fo80 to Fo60 (about 100 μm). Olivine in the groundmass is zoned from Mg# 0.55 to 0.15; its CaO content ranges 2.0 to 8.4%. Subcalcic kirschsteinite is zoned from Mg# 0.13 to 0.03, CaO increasing from 15.8 to 21.3%. Pyroxenes xenocrysts (Mg# = 0.77) are superseded in the groundmass by less magnesian pyroxenes, Mg# 0.61 to 0.17, with an average FeO/ MnO of 98. Their compositions range from En30 Fs22 Wo27 Al‐Ts28 Ti‐Ts2 to En2 Fs37 Wo22 Al‐Ts40 Ti‐Ts1. Anorthite microcrysts (An99‐100) are restricted to the groundmass. Accessories are pyrrhotite, kamacite, Ca‐phosphate, titanomagnetite, hercynite and Ca‐carbonate.

The bulk chemical composition confirms that NWA 1670 corresponds to a normal angrite melt that incorporated olivine. High Mg olivine xenocrysts and the associated mineralogy are typical of angrites. We suggest that it is an impact melt with relict phenocrysts. The strong silica undersaturation, the presence of Fo90 olivine xenocrysts and carbonate support their derivation as melilite‐like melts in the presence of carbonate.
Validation of numerical codes for impact and explosion cratering: Impacts on strengthless and metal targets
Authors: PIERAZZO E. , ARTEMIEVA N. , ASPHAUG E. , BALDWIN E. C. , CAZAMIAS J. , COKER R. , COLLINS G. S. , CRAWFORD D. A. , DAVISON T. , ELBESHAUSEN D. , HOLSAPPLE K. A. , HOUSEN K. R. , KORYCANSKY D. G. , WÜNNEMANN K.
Published: January 2010

Abstract— Over the last few decades, rapid improvement of computer capabilities has allowed impact cratering to be modeled with increasing complexity and realism, and has paved the way for a new era of numerical modeling of the impact process, including full, three‐dimensional (3D) simulations. When properly benchmarked and validated against observation, computer models offer a powerful tool for understanding the mechanics of impact crater formation. This work presents results from the first phase of a project to benchmark and validate shock codes. A variety of 2D and 3D codes were used in this study, from commercial products like AUTODYN, to codes developed within the scientific community like SOVA, SPH, ZEUS‐MP, iSALE, and codes developed at U.S. National Laboratories like CTH, SAGE/RAGE, and ALE3D. Benchmark calculations of shock wave propagation in aluminum‐on‐aluminum impacts were performed to examine the agreement between codes for simple idealized problems. The benchmark simulations show that variability in code results is to be expected due to differences in the underlying solution algorithm of each code, artificial stability parameters, spatial and temporal resolution, and material models. Overall, the inter‐code variability in peak shock pressure as a function of distance is around 10 to 20%. In general, if the impactor is resolved by at least 20 cells across its radius, the underestimation of peak shock pressure due to spatial resolution is less than 10%. In addition to the benchmark tests, three validation tests were performed to examine the ability of the codes to reproduce the time evolution of crater radius and depth observed in vertical laboratory impacts in water and two well‐characterized aluminum alloys. Results from these calculations are in good agreement with experiments. There appears to be a general tendency of shock physics codes to underestimate the radius of the forming crater. Overall, the discrepancy between the model and experiment results is between 10 and 20%, similar to the inter‐code variability.
The effect of target properties on crater morphology: Comparison of central peak craters on the Moon and Ganymede
Authors: BRAY Veronica J. , COLLINS Gareth S. , MORGAN Joanna V. , SCHENK Paul M.
Published: January 2010

Abstract— We examine the morphology of central peak craters on the Moon and Ganymede in order to investigate differences in the near‐surface properties of these bodies. We have extracted topographic profiles across craters on Ganymede using Galileo images, and use these data to compile scaling trends. Comparisons between lunar and Ganymede craters show that crater depth, wall slope and amount of central uplift are all affected by material properties. We observe no major differences between similar‐sized craters in the dark and bright terrain of Ganymede, suggesting that dark terrain does not contain enough silicate material to significantly increase the strength of the surface ice. Below crater diameters of ˜12 km, central peak craters on Ganymede and simple craters on the Moon have similar rim heights, indicating comparable amounts of rim collapse. This suggests that the formation of central peaks at smaller crater diameters on Ganymede than the Moon is dominated by enhanced central floor uplift rather than rim collapse. Crater wall slope trends are similar on the Moon and Ganymede, indicating that there is a similar trend in material weakening with increasing crater size, and possibly that the mechanism of weakening during impact is analogous in icy and rocky targets. We have run a suite of numerical models to simulate the formation of central peak craters on Ganymede and the Moon. Our modeling shows that the same styles of strength model can be applied to ice and rock, and that the strength model parameters do not differ significantly between materials.
Laboratory investigations of marine impact events: Factors influencing crater formation and projectile survivability
Authors: MILNER D. J. , BALDWIN E. C. , BURCHELL M. J.
Published: January 2010

Abstract— Given that the Earth's surface is covered in around two‐thirds water, the majority of impact events should have occurred in marine environments. However, with the presence of a water layer, crater formation may be prohibited. Indeed, formation is greatly controlled by the water depth to projectile diameter ratio, as discussed in this paper. Previous work has shown that the underlying target material also influences crater formation (e.g., Gault and Sonett 1982; Baldwin et al. 2007). In addition to the above parameters we also show the influence of impact angle, impact velocity and projectile density for a variety of water depths on crater formation and projectile survivability. The limiting ratio of water depth to projectile diameter on cratering represents the point at which the projectile is significantly slowed by transit through the water layer to reduce the impact energy to that which prohibits cratering. We therefore study the velocity decay produced by a water layer using laboratory, analytical and numerical modelling techniques, and determine the peak pressures endured by the projectile. For an impact into a water depth five times the projectile diameter, the velocity of the projectile is found to be reduced to 26–32% its original value. For deep water impacts we find that up to 60% of the original mass of the projectile survives in an oblique impact, where survivability is defined as the solid or melted mass fraction of the projectile that could be collected after impact.
Asymmetric signatures in simple craters as an indicator for an oblique impact direction
Authors: POELCHAU Michael H. , KENKMANN Thomas
Published: January 2010

Abstract— In oblique impacts with an impact angle under 45°, the bilateral shape of the distal ejecta blanket is used as the strongest indicator for an impact vector. This bilateral symmetry is attenuated and is superimposed by radial symmetry towards the crater rim, which remains circular for impact angles down to 10–15°. The possibility that remnants of bilateral symmetry might still be present in the most proximal ejecta, the overturned flap and the crater rim was explored with the intention of deducing an impact vector. A model is presented that postulates bilateral patterns using proximal ejecta trajectories and predicts these patterns in the orientation of bedding planes in the crater rim. This model was successfully correlated to patterns described by radial grooves in the proximal ejecta blanket of the oblique Tooting crater on Mars. A new method was developed to detect structural asymmetries by converting bedding data into values that express the deviation from concentric strike orientation in the crater rim relative to the crater center, termed “concentric deviation.” The method was applied to field data from Wolfe Creek crater, Western Australia. Bedding in the overturned flap implies an impactor striking from the east, which refines earlier publications, while bedding from the inner rim shows a correlation with the crater rim morphology.
The Dakhleh Glass: Product of an impact airburst or cratering event in the Western Desert of Egypt?
Authors: OSINSKI Gordon R. , KIENIEWICZ Johanna , SMITH Jennifer R. , BOSLOUGH Mark B. E. , ECCLESTON Mark , SCHWARCZ Henry P. , KLEINDIENST Maxine R. , HALDEMANN Albert F. C. , CHURCHER Charles S.
Published: January 2010

Abstract— Impact cratering is a ubiquitous geological process on the terrestrial planets. Meteorite impact craters are the most visible product of impact events, but there is a growing recognition that large aerial bursts or airbursts should occur relatively frequently throughout geological time. In this contribution, we report on an unusual impact glass‐the Dakhleh Glass (DG)–which is distributed over an area of ˜400 km 2of the Dakhleh Oasis, Egypt. This region preserves a rich history of habitation stretching back to over 400,000 years before the emergence of Homo sapiens. We report on observations made during recent fieldwork and subsequent analytical analyses that strengthen previous suggestions that the DG formed during an impact event. The wide distribution and large size of DG specimens (up to ˜50 cm across), the chemistry (e.g., CaO and Al2O3 contents up to ˜25 and ˜18 wt, respectively), the presence of lechatelierite and burnt sediments, and the inclusion of clasts and spherules in the DG is inconsistent with known terrestrial processes of glass formation. The age and other textural characteristics rule out a human origin. Instead, we draw upon recent numerical modeling of airbursts to suggest that the properties of DG, coupled with the absence of a confirmed crater, can best be explained by melting of surficial sediments as a result of a large airburst event. We suggest that glass produced by such events should, therefore, be more common in the rock record than impact craters, assuming that the glass formed in a suitable preserving environment.
Geochemistry and origin of metal, olivine clasts, and matrix in the Dong Ujimqin Qi mesosiderite
Authors: Kong Ping , Su Wen , Li Xianhua , Spettel Bernhard , Palme Herbert , Tao Kejie
Published: January 2010

Abstract— The Dong Ujimqin Qi mesosiderite is the first recorded fall of a stony‐iron meteorite in China. According to silicate textures and metal composition, this meteorite is classified as a member of subgroup IB. Instrumental neutron activation analyses (INAA) of metals show that the matrix metal has lower concentrations of Os, Ir, Re, and Pt, but higher concentrations of Ni and Au than the 7.5 cm metal nodule present in the meteorite. We attribute these compositional differences to fractional crystallization of molten metal. Studies of olivine clasts show that FeO contents are uniform in individual olivine crystals but are variable for different olivine clasts. Although concentrations of rare earth elements (REEs) change within olivine clasts, they all exhibit a vee‐shaped pattern relative to CI chondrites. The relatively high concentrations of REEs in olivine and the shape of REE patterns require a liquid high in REEs and especially in light REEs. As such a liquid was absent from the region where basaltic and gabbroic clasts formed, mesosiderite olivine must have formed in a part of the differentiated asteroid that is different from the location where other mesosiderite silicate clasts formed.
Geochemistry of Darwin glass and target rocks from Darwin crater, Tasmania, Australia
Authors: Howard Kieren T.
Published: January 2010

Abstract—Darwin glass formed about 800,000 years ago in western Tasmania, Australia. Target rocks at Darwin crater are quartzites and slates (Siluro‐Devonian, Eldon Group). Analyses show 2 groups of glass, Average group 1 is composed of: SiO2(85%), Al2O3(7.3%), TiO2(0.05%), FeO (2.2%), MgO (0.9%), and K2O (1.8%). Group 2 has lower average SiO2(81.1%) and higher average Al2O3(8.2%). Group 2 is enriched in FeO (+1.5%), MgO (+1.3%) and Ni, Co, and Cr. Average Ni (416 ppm), Co (31 ppm), and Cr (162 ppm) in group 2 are beyond the range of sedimentary rocks. Glass and target rocks have concordant REE patterns (La/Lu = 5.9–10; Eu/Eu* = 0.55–0.65) and overlapping trace element abundances. 87Sr/86Sr ratios for the glasses (0.80778–0.81605) fall in the range (0.76481–1.1212) defined by the rock samples. ε‐Nd results range from –13.57 to –15.86. Nd model ages range from 1.2–1.9 Ga (CHUR) and the glasses (1.2–1.5 Ga) fall within the range defined by the target samples. The87Sr/86Sr versus 87Rb/86Sr regression age (411 ± 42 Ma) and initial ratio (0.725 ± 0.016), and the initial43Nd/144Nd ratio (0.51153 ± 000011) and regression age (451 ± 140 Ma) indicate that the glasses have an inherited isotopic signal from the target rocks at Darwin crater. Mixing models using target rock compositions successfully model the glass for all elementsexcept FeO, MgO, Ni, Co, and Cr in group 2. Mixing models using terrestrial ultramafic rocks fail to match the glass compositions and these enrichments may be related to the projectile.
A database of chondrite analyses including platinum group elements, Ni, Co, Au, and Cr: Implications for the identification of chondritic projectiles
Authors: Tagle Roald , Berlin Jana
Published: January 2010

Abstract— Siderophile elements have been used to constrain projectile compositions in terrestrial and lunar impact melt rocks. To obtain a better knowledge of compositional differences between potential chondritic projectile types, meteorite analyses of the elements Ru, Rh, Pd, Os, Ir, Pt, Cr, Co, Ni, and Au were gathered into a database. The presented compilation comprises 806 analyses of 278 chondrites including new ICP‐MS analyses of Allende and two ordinary chondrites. Each data set was evaluated by comparing element ratios of meteorites from the same chondrite group. Characteristic element abundances and ratios were determined for each group. Features observed in the element abundance patterns can be linked directly to the presence of certain components, such as the abundance of refractory elements Os, Ir, and Ru correlating with the occurrence of refractory inclusions in CV, CO, CK, and CM chondrites. The refined characteristic element ratios appear to be representative not only for meteorites, but also for related asteroidal bodies. Chondrite element ratios were compared to previously published values from impact melt rocks of the Popigai and Morokweng impact structures confirming that an identification of the specific type of projectile (L and LL chondrite, respectively) is possible. The assessment for Morokweng is supported by the recent discovery of an LL chondrite fragment in the impact melt rocks. Ultimately, the database provides valuable information for understanding processes in the solar nebula as they are recorded in chondrites. A new type of complementarity between element patterns of CK and EH chondrites is suggested to be the result of condensation, redox, and transportation processes in the solar nebula.
Radial transport in the solar nebula: Implications for moderately volatile element depletions in chondritic meteorites
Authors: CIESLA Fred J.
Published: January 2010

Abstract— In this paper, we explore the possibility that the moderately volatile element depletions observed in chondritic meteorites are the result of planetesimals accreting in a solar nebula that cooled from an initially hot state (temperatures > 1350 K out to ˜2–4 AU). A model is developed to track the chemical inventory of planetesimals that accrete in a viscously evolving protoplanetary disk, accounting for the redistribution of solids and vapor by advection, diffusion, and gas drag. It is found that depletion trends similar to those observed in the chondritic meteorites can be reproduced for a small range of model parameters. However, the necessary range of parameters is inconsistent with observations of disks around young stars and other constraints on meteorite parent body formation. Thus, counter to previous work, it is concluded that the global scale evolution of the solar nebula is not the cause for the observed depletion trends. Instead, it appears that localized processing must be considered.
182Hf‐182W chronometry and the early evolution history in the acapulcoite‐lodranite parent body
Authors: LEE Der‐Chuen
Published: January 2010

Abstract— An acapulcoite, Northwest Africa (NWA) 725, a transitional acapulcoite, Graves Nunataks (GRA) 95209, and a lodranite, NWA 2235, have been studied with the short‐lived chronometer 182Hf‐182W system in order to better constrain the early evolution history in the acapulcoite‐lodranite parent body. Unlike the more evolved achondrites originating from differentiated asteroids—e.g., eucrites and angrites—bulk rock acapulcoites and lodranite are characterized by distinct 182W deficits relative to the terrestrial W, as well as to the undifferentiated chondrites, εw varies from −2.7 to −2.4. This suggests that live‐182Hf was present during the formation of acapulcoites and lodranites, and their parent body probably had never experienced a global melting event. Due to the large uncertainties associated with the isochron for each sample, the bulk isochron that regressed through the mineral separates from all 3 samples has provided the best estimate to date for the timing of metamorphism in the acapulcoite‐lodranite parent body, 5 (+6/‐5) Myr after the onset of the solar system. It is thus inconclusive whether acapulcoites and lodranites have shared the same petrogenetic origin, based on the Hf‐W data of this study. Nevertheless, the formation of acapulcoite‐lodranite clan appears to have post‐dated the metal‐silicate segregation in differentiated asteroids. This can be explained by a slower accretion rate for the acapulcoite‐lodranite parent body, or that it had never accreted to a critical mass that could allow the metal‐silicate segregation to occur naturally.
Noble gases in Grant and Carbo and the influence of S‐ and P‐rich mineral inclusions on the 41K‐40K dating system
Authors: AMMON Katja , MASARIK Jozef , LEYA Ingo
Published: January 2010

Abstract— Cosmogenic He, Ne, and Ar were measured in the iron meteorites Grant (IIIAB) and Carbo (IID) to re‐determine their preatmospheric geometries and exposure histories. We also investigated the influence of sulphur‐ and/or phosphorus‐rich inclusions on the production rates of cosmogenic Ne. Depth profiles measured in Grant indicate a preatmospheric center location 117 mm left from the reference line and 9 mm below bar B, which is clearly different (˜10 cm) from earlier results (˜165 mm left from the reference line on bar F). For Carbo the preatmospheric center location was found to be 120 mm right of the reference line and 15 mm above bar J, which is in agreement with literature data. The new measurements indicate a spherical preatmospheric shape for both meteorites and, based on literature 36C1 data, the radii were estimated to be about 32 cm and 70 cm for Grant and Carbo, respectively. We demonstrate that minor elements like S and P have a significant influence on the production rates of cosmogenic Ne. In our samples, containing on average 0.5% S and/or P, about 20% of 21Ne was produced from these minor elements. Using measured 21Ne concentrations and endmember 22Ne/21Ne ratios for Fe + Ni and S + P, respectively, we show that it is possible to correct for 21Ne produced from S and/or P. The thus corrected data are then used to calculate new 41K‐40K exposure ages—using published K data—which results in 564 ± 78 Ma for Grant and 725 ± 100 Ma for Carbo. The correction always lowers the 21Ne concentrations and consequently decreases the 41K‐40K exposure ages. The discrepancies between 36Cl‐36Ar and 41K‐40K ages are accordingly reduced. The existence of a significant long‐term variation of the GCR, which is based on a former 30–50% difference between 41K‐40K and 36Cl‐36Ar ages, may warrant re‐investigation.
Structural evolution of the 40 km wide Araguainha impact structure, central Brazil
Authors: LANA C. , FILHO C. R. SOUZA , MARANGONI Y. R. , YOKOYAMA E. , TRINDADE R. I. F. , TOHVER E. , REIMOLD W. U.
Published: January 2010

Abstract— The 40 km wide Araguainha structure in central Brazil is a shallowly eroded impact crater that presents unique insights into the final stages of complex crater formation. The dominant structural features preserved at Araguainha relate directly to the centripetal movement of the target rocks during the collapse of the transient cavity. Slumping of the transient cavity walls resulted in inward‐verging inclined folds and a km‐scale anticline in the outer ring of the structure. The folding stage was followed by radial and concentric faulting, with downward displacement of kilometer‐scale blocks around the crater rim. The central uplift records evidence for km‐scale upward movement of crystalline basement rocks from the transient cavity floor, and lateral moment of sedimentary target rocks detached from the cavity walls. Much of the structural grain in the central uplift relates to structural stacking of km‐scale thrust sheets of sedimentary strata onto the core of crystalline basement rocks. Outward‐plunging radial folds indicate tangential oblate shortening of the strata during the imbrication of the thrust sheets. Each individual sheet records an early stage of folding and thickening due to non‐coaxial strains, shortly before sheet imbrication. We attribute this folding and thickening phase to the kilometer‐scale inward movement of the target strata from the transient cavity walls to the central uplift. The outer parts of the central uplift record additional outward movement of the target rocks, possibly related to the collapse of the central uplift. An inner ring structure at 10–12 km from the crater center marks the extent of the deformation related to the outward movement of the target rocks.
Kinetic stability of a melted iron globule during chondrule formation. I. Non‐rotating model
Authors: UESUGI Masayuki , SEKIYA Minoru , NAKAMURA Tomoki
Published: January 2010

Abstract— We have investigated the kinematics of the separation of iron globules from chondrules during chondrule formation. A simple model, which assumes that the system has no angular momentum, was used to calculate the energy of a system with an iron globule and a chondrule. The energies of three different states were calculated: 1) a melted iron globule fully embedded in a melted chondrule, 2) a melted iron globule on the surface of a melted chondrule, and 3) a melted iron globule being separated from a melted chondrule. We also calculated the lowest energy shape for a melted iron globule on the surface of a melted chondrule, and compared our result with the shapes of four natural samples of chondrules and iron globules in thin sections. The shapes were calculated using an assumed value for the interface energy between the four couples of melted chondrules and the iron globules, and agree well with the natural shapes of chondrules and iron globules. The results of our calculations show that the iron globules of these four samples would be strongly bound to the surface of the melted chondrule during chondrule formation, and separation would be difficult, if the iron globules had been on the surface of precursors of these chondrules. Our results also show that if these iron globules were initially inside and transported to the surface of the melted chondrule, most of them would be ejected from the inside to outside because of surface tension forces, as long as the energy losses due to viscous dissipation when the globules pass through the surface of melted chondrules were sufficiently small.

Although further improvement of the model is required, our results demonstrate that this ejection process may be responsible for the depletion of siderophile elements in natural chondrules.
Characterizing and navigating small bodies with imaging data
Authors: GASKELL R. W. , BARNOUIN‐JHA O. S. , SCHEERES D. J. , KONOPLIV A. S. , MUKAI T. , ABE S. , SAITO J. , ISHIGURO M. , KUBOTA T. , HASHIMOTO T. , KAWAGUCHI J. , YOSHIKAWA M. , SHIRAKAWA K. , KOMINATO T. , HIRATA N. , DEMURA H.
Published: January 2010

Abstract— Recent advances in the characterization of small body surfaces with stereophotoclinometry are discussed. The principal data output is an ensemble of landmark maps (L‐maps), high‐resolution topography/albedo maps of varying resolution that tile the surface of the body. Because they can have a resolution comparable to the best images, and can be located on a global reference frame to high accuracy, L‐maps provide a significant improvement in discriminatory power for studies of small bodies, ranging from regolith processes to interior structure. These techniques are now being used to map larger bodies such as the Moon and Mercury.

L‐maps are combined to produce a standard global topography model (GTM) with about 1.57 million vectors and having a wide variety of applications. They can also be combined to produce high‐resolution topography maps that describe local areas with much greater detail than the GTM. When combined with nominal predictions from other data sources and available data from other instruments such as LIDAR or RADAR, solutions for the spacecraft position and camera pointing are the most accurate available. Examples are drawn from studies of Phobos, Eros, and Itokawa, including surface characterization, gravity analysis, spacecraft navigation, and incorporation of LIDAR or RADAR data. This work has important implications for potential future missions such as Deep Interior and the level of navigation and science that can be achieved.
Critical crater diameter and asteroid impact seismology
Authors: ASPHAUG Erik
Published: January 2010

Abstract— If impact stress reverberation is the primary gradational process on an asteroid at global scales, then the largest undegraded crater records an asteroid's seismological response. The critical crater diameter Dcrit is defined as the smallest crater whose formation disrupts all previous craters globally up to its size; it is solved for by combining relationships for crater growth and for stress attenuation. The computation for Dcrit gives a simple explanation for the curious observation that small asteroids have only modest undegraded craters, in comparison to their size, whereas large asteroids have giant undegraded craters. Dcrit can even exceed the asteroid diameter, in which case all craters are “local” and the asteroid becomes crowded with giant craters. Dcrit is the most recent crater to have formed on a blank slate; when it is equated to the measured diameter of the largest undegraded crater on known asteroids, peak particle velocities are found to attenuate with the 1.2–1.3 power of distance—less attenuative than strong shocks, and more characteristic of powerful seismic disturbances. This is to be expected, since global degradation can result from seismic (cm s−1) particle velocities on small asteroids. Attenuation, as modeled, appears to be higher on asteroids known to be porous, although these are also bodies for which different crater scaling rules might apply.
Valence state partitioning of V between pyroxene‐melt: Effects of pyroxene and melt composition, and direct determination of V valence states by XANES. Application to Martian basalt QUE 94201 composition
Authors: KARNER J. M. , PAPIKE J. J. , SUTTON S. R. , SHEARER C. K. , BURGER P. , McKAY G. , LE L.
Published: January 2010

Abstract— Experiments on a Martian basalt composition show that Dv augite/melt is greater than Dv pigeonite/melt in samples equilibrated under the same fO2 conditions. This increase is due to the increased availability of elements for coupled substitution with the V3+ or V4+ ions, namely A1 and Na. For this bulk composition, both A1 and Na are higher in concentration in augite compared with pigeonite; therefore more V can enter augite than pigeonite. Direct valence state determination by XANES shows that the V3+ and V4+ are the main V species in the melt at fO2 conditions of IW‐1 to IW+3.5, whereas pyroxene grains at IW‐1, IW, and IW+1 contain mostly V3+. This confirms the idea that V3+ is more compatible in pyroxene than V4+. The XANES data also indicates that a small percentage of V2+ may exist in melt and pyroxene at IW‐1. The similar valence of V in glass and pyroxene at IW‐1 suggests that V2+ and V3+ may have similar compatibilities in pyroxene.
The complex exposure histories of the Pitts and Horse Creek iron meteorites: Implications for meteorite delivery models
Authors: WELTEN K. C. , NISHIIZUMI K. , LAVIELLE B. , CAFFEE M. W. , HILLEGONDS D. J. , FINKEL R. C. , KOLLAR D. , MASARIK J.
Published: January 2010

Abstract— The concentrations of cosmogenic radionuclides and noble gases in Pitts (IAB) and Horse Creek (ungrouped) provide unambiguous evidence that both irons have a complex exposure history with a first‐stage irradiation of 100–600 Myr under high shielding, followed by a second‐stage exposure of ˜1 Myr as small objects. The first‐stage exposure ages of ˜100 Myr for Horse Creek and ˜600 Myr for Pitts are similar to cosmic‐ray exposure ages of other iron meteorites, and most likely represent the Yarkovsky orbital drift times of irons from their parent bodies in the main asteroid belt to one of the nearby chaotic resonance zones. The short second‐stage exposure ages indicate that collisional debris from recent impact events on their precursor objects was quickly delivered to Earth. The short delivery times suggests that the recent collision events occurred while the precursor objects of Horse Creek and Pitts were either very close to the chaotic resonance zones or already in Earth‐crossing orbits. Since the cosmogenic noble gas records of Horse Creek and Pitts indicate a minimum radius of a few meters for the precursor objects, but do not exclude km‐sized objects, we conclude that these irons may represent fragments of two near‐Earth asteroids, 3103 Eger and 1986 DA, respectively. Finally, we used the cosmogenic nuclide concentrations in Horse Creek, which contains 2.5 wt% Si, to test current model calculations for the production of cosmogenic 10Be, 26Al, and neonisotopes from iron, nickel, and silicon.
Oxygen isotope anomalies of the Sun and the original environment of the solar system
Authors: LEE Jeong‐Eun , BERGIN Edwin A. , LYONS James R.
Published: January 2010

Abstract— We present results from a model of oxygen isotopic anomaly production through selective photodissociation of CO within the collapsing proto‐solar cloud. Our model produces a proto‐Sun with a wide range of Δ17O values depending on the intensity of the ultraviolet radiation field. Dramatically different results from two recent solar wind oxygen isotope measurements indicate that a variety of compositions remain possible for the solar oxygen isotope composition. However, constrained by other measurements from comets and meteorites, our models imply the birth of the Sun in a stellar cluster with an enhanced radiation field and are therefore consistent with a supernova source for 60Fe in meteorites.