bluuebunny/crossref_metadata_2025 huggingface dataset:
Condensation processes in astrophysical environments: The composition and structure of cometary grains
Authors: NUTH Joseph A. , RIETMEIJER Frans J. M. , HILL Hugh G. M.
Published: January 2010

Abstract— We review the results of our recent experimental studies of astrophysical dust analogs. We discuss the condensation of amorphous silicates from mixed metal vapors, including evidence that such condensates form with metastable eutectic compositions. We consider the spectral evolution of amorphous magnesium silicate condensates as a function of time and temperature. Magnesium silicate smokes anneal readily at temperatures of about 1000–1100 K. In contrast we find that iron silicates require much higher temperatures (˜1300 K) to bring about similar changes on the same timescale (days to months). We first apply these results to infrared space observatory observations of crystalline magnesium silicate grains around high‐mass‐outflow asymptotic giant branch stars in order to demonstrate their general utility in a rather simple environment. Finally, we apply these experimental results to infrared observations of comets and protostars in order to derive some interesting conclusions regarding large‐scale nebular dynamics, the natural production of organic molecules in protostellar nebulae, and the use of crystalline magnesium silicates as a relative indicator of a comet's formation age.
Low‐temperature crystallization of MgSiO3 glasses under electron irradiation: Possible implications for silicate dust evolution in circumstellar environments
Authors: CARREZ Philippe , DEMYK Karine , LEROUX Hugues , CORDIER Patrick , JONES Anthony P. , D'HENDECOURT Louis
Published: January 2010

Abstract— Synthetic MgSiO3 glasses were irradiated at room temperature by 300 keV electrons in a transmission electron microscope (TEM). One of the samples had been previously irradiated by 50 keV He+ ions. Electron irradiation induces the nucleation and growth of randomly oriented nanometer‐sized crystallites. The crystallites first consist of MgO and subsequently of forsterite (Mg2SiO4). Both are seen to form within an amorphous SiO2 matrix. The rate of crystallization of the samples has been monitored by conventional TEM imaging and electron diffraction. The sample that had been pre‐irradiated with He+ ions is found to transform faster than the as‐quenched glass. The crystallization of metastable MgSiO3 glasses is explained by ionizing radiation‐induced elemental diffusion that allows the reorganization of matter into a more favourable thermodynamic state. These results show that ionizing radiation interactions could account for crystal formation as observed in infrared spectroscopy in some young stellar environments.
The irradiation history of the Ghubara (L5) regolith breccia
Authors: Ferko T. E. , Wang M‐S. , Hillegonds D. J. , Lipschutz M. E. , Hutchison R. , Franke L. , Scherer P. , Schultz L. , Benoit P. H. , Sears D. W. G. , Singhvi A. K. , Bhandari N.
Published: January 2010

Abstract— We measured cosmic‐ray products—noble gases, radionuclides, thermoluminescence, and nuclear tracks—and trace element contents and mineralogy of samples of three orthogonal and mutually intersecting cores (41–46 cm long) of a 101.6 kg Ghubara individual (1958,805) at The Natural History Museum, London. The xenoliths, like the host, have high concentrations of trapped solar gases and are heavily shocked. While contents of noble gases and degree of shock‐loading in this individual and three others differ somewhat, the data indicate that Ghubara is a two‐generation regolith breccia. Contents of cosmogenic 26Al and 10Be and low track densities indicate that the Ghubara individuals were located more than 15 cm below the surface of an 85 cm meteoroid. Because of its large size, Ghubara's cosmic‐ray exposure age is poorly defined to be 15–20 Ma from cosmogenic nuclides. Ghubara's terrestrial age, based on 14C data, is 2–3 ka. Not only is Ghubara the first known case of a two‐generation regolith breccia on the macroscale, it also has a complicated thermal and irradiation history.
Impact processing of chondritic planetesimals: Siderophile and volatile element fractionation in the Chico L chondrite
Authors: Norman Marc D. , Mittlefehldt David W.
Published: January 2010

Abstract— A large impact event 500 Ma ago shocked and melted portions of the L‐chondrite parent body. Chico is an impact melt breccia produced by this event. Sawn surfaces of this 105 kg meteorite reveal a dike of fine‐grained, clast‐poor impact melt cutting shocked host chondrite. Coarse (1–2 cm diameter) globules of FeNi metal + sulfide are concentrated along the axis of the dike from metal‐poor regions toward the margins. Refractory lithophile element abundance patterns in the melt rock are parallel to average L chondrites, demonstrating near‐total fusion of the L‐chondrite target by the impact and negligible crystal‐liquid fractionation during emplacement and cooling of the dike.

Significant geochemical effects of the impact melting event include fractionation of siderophile and chalcophile elements with increasing metal‐silicate heterogeneity, and mobilization of moderately to highly volatile elements. Siderophile and chalcophile elements ratios such as Ni/Co, Cu/Ga, and Ir/Au vary systematically with decreasing metal content of the melt. Surprisingly small (˜102) effective metal/silicate‐melt distribution coefficients for highly siderophile elements probably reflect inefficient segregation of metal despite the large degrees of melting. Moderately volatile lithophile elements such K and Rb were mobilized and heterogeneously distributed in the L‐chondrite impact breccias whereas highly volatile elements such as Cs and Pb were profoundly depleted in the region of the parent body sampled by Chico. Volatile element variations in Chico and other L chondrites are more consistent with a mechanism related to impact heating rather than condensation from a solar nebula. Impact processing can significantly alter the primary distributions of siderophile and volatile elements in chondritic planetesimals.
Petrology and geochemistry of D'Orbigny, geochemistry of Sahara 99555, and the origin of angrites
Authors: Mittlefehldt David W. , Killgore Marvin , Lee Michael T.
Published: January 2010

Abstract— We have done a detailed petrologic study of the angrite, D'Orbigny, and geochemical study of it and Sahara 99555. D'Orbigny is an igneous‐textured rock composed of Ca‐rich olivine, Al‐Ti‐diopside‐hedenbergite, subcalcic kirschsteinite, two generations of hercynitic spinel and anorthite, with the mesostasis phases ulvöspinel, Ca‐phosphate, a silico‐phosphate phase and Fe‐sulfide. We report an unknown Fe‐Ca‐Al‐Ti‐silicate phase in the mesostasis not previously found in angrites. One hercynitic spinel is a large, rounded homogeneous grain of a different composition than the euhedral and zoned grains. We believe the former is a xenocryst, the first such described from angrites. The mafic phases are highly zoned; mg# of cores for olivine are ˜64, and for clinopyroxene ˜58, and both are zoned to Mg‐free rims. The Ca content of olivine increases with decreasing mg#, until olivine with ˜20 mol% Ca is overgrown by subcalcic kirschsteinite with about 30–35 mol% Ca. Detailed zoning sequences in olivine‐subcalcic kirschsteinite and clinopyroxene show slight compositional reversals. There is no mineralogic control that can explain these reversals, and we believe they were likely caused by local additions of more primitive melt during crystallization of D'Orbigny.

D'Orbigny is the most ferroan angrite with a bulk rock mg# of 32. Compositionally, it is virtually identical to Sahara 99555; they are the first set of compositionally identical angrites. Comparison with the other angrites shows that there is no simple petrogenetic sequence, partial melting with or without fractional crystallization, that can explain the angrite suite. Angra dos Reis remains an anomalous angrite.

Angrites show no evidence for the brecciation, shock, impact metamorphism, or thermal metamorphism that affected the howardite, eucrite, diogenite (HED) suite and ordinary chondrites. This suggests that the angrite parent body may have followed a fundamentally different evolutionary path than did these other parent bodies.
Northwest Africa 032: Product of lunar volcanism
Authors: Fagan T. J. , Taylor G. J. , Keil K. , Bunch T. E. , Wittke J. H. , Korotev R. L. , Jolliff B. L. , Gillis J. J. , Haskin L. A. , Jarosewich E. , Clayton R. N. , Mayeda T. K. , Fernandes V. A. , Burgess R. , Turner G. , Eugster O. , Lorenzetti S.
Published: January 2010

Abstract— Mineralogy, major element compositions of minerals, and elemental and oxygen isotopic compositions of the whole rock attest to a lunar origin of the meteorite Northwest Africa (NWA) 032, an unbrecciated basalt found in October 1999. The rock consists predominantly of olivine, pyroxene and chromite phenocrysts, set in a crystalline groundmass of feldspar, pyroxene, ilmenite, troilite and trace metal. Whole‐rock shock veins comprise a minor, but ubiquitous portion of the rock. Undulatory to mosaic extinction in olivine and pyroxene phenocrysts and micro‐faults in groundmass and phenocrysts also are attributed to shock.

Several geochemical signatures taken together indicate unambiguously that NWA 032 originated from the Moon. The most diagnostic criteria include whole‐rock oxygen isotopic composition and ratios of Fe/Mn in the whole rock, olivine, and pyroxene. A lunar origin is documented further by the presence of Fe‐metal, troilite, and ilmenite; zoning to extremely Fe‐rich compositions in pyroxene; the ferrous oxidation state of all Fe in pyroxene; and the rare earth element (REE) pattern with a well‐defined negative europium anomaly. This rock is similar in major element chemistry to basalts from Apollo 12 and 15, but is enriched in light REE and has an unusually high Th/Sm ratio. Some Apollo 14 basalts yield a closer match to NWA 032 in REE patterns, but have higher concentrations of Al2O3. Ar‐Ar step release results are complex, but yield a whole‐rock age of ˜2.8 Ga, suggesting that NWA 032 was extruded at 2.8 Ga or earlier. This rock may be the youngest sample of mare basalt collected to date. Noble gas concentrations combined with previously collected radionuclide data indicate that the meteorite exposure history is distinct from currently recognized lunar meteorites. In short, the geochemical and petrographic features of NWA 032 are not matched by Apollo or Luna samples, nor by previously identified lunar meteorites, indicating that it originates from a previously unsampled mare deposit.

Detailed assessment of petrographic features, olivine zoning, and thermodynamic modelling indicate a relatively simple cooling and crystallization history for NWA 032. Chromite‐spinel, olivine, and pyroxene crystallized as phenocrysts while the magma cooled no faster than 2 °C/h based on the polyhedral morphology of olivine. Comparison of olivine size with crystal growth rates and preserved Fe‐Mg diffusion profiles in olivine phenocrysts suggest that olivine was immersed in the melt for no more than 40 days. Plumose textures in groundmass pyroxene, feldspar, and ilmenite, and Fe‐rich rims on the phenocrysts formed during rapid crystallization (cooling rates ˜20 to 60 °C/h) after eruption.
Space shuttle observations of terrestrial impact structures using SIR‐C and X‐SAR radars
Authors: Mchone John F. , Greeley Ronald , Williams Kevin K. , Blumberg Dan G. , Kuzmin Ruslan O.
Published: January 2010

Abstract— Ten terrestrial impact structures were imaged during two flights of the 1994 space radar laboratory (SRL) experiment. These craters include Wolf Creek, Australia; Roter Kamm, Namibia; Zhamanshin, Kazakhstan; BP and Oasis, Libya; Aorounga, Chad; Amguid, Algeria; and Spider, Connolly Basin and Henbury, Australia. SRL contained two co‐registered instruments; the United States shuttle imaging radar‐C (SIR‐C) polarimetric radar system operating in L‐band (λ = 24 cm) and C‐band (λ = 5.6 cm), and the joint German/Italian synthetic aperture radar (X‐SAR) operating in vertically‐polarized X‐band (λ = 3 cm).

Comparisons show SRL images to be complementary to, or in some cases superior to, corresponding optical images for evaluating size, location, and relative age of impact features. Regardless of wavelength or polarization, craters with significant relief appear prominently on radar as a result of slope and roughness effects. In desert regions, longer wavelengths penetrate dry sand mantles to reveal hidden crater dimensions or associated buried landforms. Radar polarities and wavelengths are particularly sensitive to vegetation, surface roughness, and soil moisture or electrical properties. In the more temperate environments of Kazakhstan and Australia, SRL images show detailed stream patterns that reveal the location and structure of otherwise obscured impact features.
Fall, classification and cosmogenic records of the Sabrum (LL6) chondrite
Authors: Ghosh S. , Murty S. V. S. , Shukla P. N. , Shukla A. D. , Mahajan R. R. , Bhandari N. , Pant N. C. , Ghosh J. B. , Shome S.
Published: January 2010

Abstract— The petrographic and chemical characteristics of a fresh Indian meteorite fall at Sabrum are described. Its mean mineral composition is defined by olivine (Fa31.4), orthopyroxene (Fs25.1,Wo2.0), clinopyroxene (Wo45En45.6Fs9.4) and plagioclase (An10.6Ab83.6Or5.8). The meteorite shows moderate shock features, which indicate that it belongs to the S4 category. Based on mineralogical and chemical criteria the meteorite is classified as an LL6 brecciated veined chondrite. Several cosmogenic radioisotopes (46Sc, 7Be, 54Mn, 22Na and 26Al), noble gas (He, Ne, Ar, Kr and Xe), nitrogen isotopes, and particle tracks density have been measured. Concentrations of cosmogenic 21Ne and 38Ar indicate that its cosmic‐ray exposure age is 24.8 Ma. Small amounts of trapped Kr and Xe, consistent with petrologic class 5/6, are present. The track density in olivines is found to be (1.3 ± 0.3) × 106/cm2. Activities of most of the short‐lived isotopes are lower than those expected from solar cycle variation. 22Na/26Al (1.12 ± 0.02) is found to be significantly anomalous, being ˜25% lower than expected from the Climax neutron monitor data. These results indicate that the cosmic‐ray flux during the terminal segment of the meteoroid orbit was low. The activities of 26Al and 60Co and the track density indicate small meteoroid size with a radius ˜15 cm.
Clearwater East impact structure: A re‐interpretation of the projectile type using new platinum‐group element data from meteorites
Authors: McDonald Iain
Published: January 2010

Abstract— Platinum‐group element (PGE) concentrations and ratios obtained from samples of the Clearwater East impact melt have been used along with other siderophile element ratios to classify the impacting projectile as a carbonaceous chondrite. This is at odds with recent chromium isotope analyses that suggest ordinary chondrite‐type material is present. The present study reviews and reinterprets the available PGE data in the light of new PGE data from meteorites and concludes that the PGE ratios in the impact melt are most consistent with ordinary (possibly type‐L) chondrite source material, not carbonaceous chondrites. Therefore the structure was most probably formed by the impact of an asteroid composed of material similar to ordinary chondrites.
An improved shadow measurement technique for constraining the morphometry of simple impact craters
Authors: Chappelow John E. , Sharpton Virgil L.
Published: January 2010

Abstract— The lengths of the shadows cast within simple, bowl‐shaped impact craters have been used to constrain their depths on a variety of planetary bodies. This technique, however, only yields the “true” crater depth if the shadow transects the crater center where the floor is deepest. In the past, attempts have been made to circumvent this limitation by choosing only craters where the shadow tip lies very near the crater center; but this approach may introduce serious artifacts that adversely affect the slope of the regressed depth vs. diameter data and its variance. Here we introduce an improved method for deriving depth information from shadow measurements that considers three basic shape variations of simple craters: paraboloidal, conical, and flat‐floored. We show that the shape of the cast shadow can be used to constrain crater shape and we derive improved equations for finding the depths of these simple craters.
Petrology and chemistry of the basaltic shergottite North West Africa 480
Authors: Barrat J. A. , Gillet Ph. , Sautter V. , Jambon A. , Javoy M. , Göpel C. , Lesourd M. , Keller F. , Petit E.
Published: January 2010

Abstract— North West Africa (NWA) 480 is a new martian meteorite of 28 g found in the Moroccan Sahara in November 2000. It consists mainly of large gray pyroxene crystals (the largest grains are up to 5 mm in length) and plagioclase converted to maskelynite. Excluding the melt pocket areas, modal analyses indicate the following mineral proportions: 72 vol% pyroxenes extensively zoned, 25% maskelynite, 1% phosphates (merrillite and chlorapatite), 1% opaque oxides (ilmenite, ulvöspinel and chromite) and sulfides, and 1% others such as silica and fayalite. The compositional trend of NWA 480 pyroxenes is similar to that of Queen Alexandra Range (QUE) 94201 but in NWA 480 the pyroxene cores are more Mg‐rich (En77‐En65). Maskelynites display a limited zoning (An42–50Ab54‐48Or2–4). Our observations suggest that NWA 480 formed from a melt with a low nuclei density at a slow cooling rate. The texture was achieved via a single‐stage cooling where pyroxenes grew continuously. A similar model was previously proposed for QUE 94201 by McSween et al. (1996). NWA 480 is an Al‐poor ferroan basaltic rock and resembles Zagami or Shergotty for major elements and compatible trace element abundances. The bulk rock analysis for oxygen isotopes yields Δ17O = +0.42%, a value in agreement at the high margin, with those measured on other shergottites (Clayton and Mayeda, 1996; Romanek et al., 1998; Franchi et al., 1999). Its CI‐normalized rare earth element pattern is similar to those of peridotitic shergottites such as Allan Hills (ALH)A77005, suggesting that these shergottites shared a similar parent liquid, or at least the same mantle source.
Strontium and neodymium isotopic study of Libyan Desert Glass: Inherited Pan‐African age signatures and new evidence for target material
Authors: Schaaf Peter , Müller‐Sohnius Dieter
Published: January 2010

Abstract— Libyan Desert Glass (LDG) is an impact‐related, natural glass of still unknown target material. We have determined Rb‐Sr and Sm‐Nd isotopic ratios from seven LDG samples and five associated sandstones from the LDG strewn field in the Great Sand Sea, western Egypt. Planar deformation features were recently detected in quartz from these sandstones. 87Sr/86Sr ratios and ∍‐Nd values for LDG range between 0.71219 and 0.71344, and between –16.6 and –17.8, respectively, and hence are distinct from the less radiogenic 87Sr/86Sr ratios of 0.70910–0.71053 and ∍‐Nd values from –6.9 to –9.6 for the local sandstones from the LDG strewn field. Previously published isotopic ratios from the Libyan BP and Oasis crater sandstones are generally incompatible with our LDG values. LDG formation undoubtedly occurred at 29 Ma, but neither the Rb‐Sr nor the Sm‐Nd isotopic system were rehomogenised during the impact event, as we can deduce from Pan‐African ages of ˜540 Ma determined from the regression lines from a total of 14 LDG samples from this work and the literature. Together with similar Sr and Nd isotopic values for LDG and granitoid rocks from northeast Africa west of the Nile, these findings point to a sandy matrix target material for the LDG derived from a Precambrian crystalline basement, ruling out the Cretaceous sandstones of the former “Nubian Group” as possible precursors for LDG.
Geochemistry of the ungrouped carbonaceous chondrite Tagish Lake, the anomalous CM chondrite Bells, and comparison with CI and CM chondrites
Authors: Mittlefehldt David W.
Published: January 2010

Abstract— I have determined the composition via instrumental neutron activation analysis of a bulk pristine sample of the Tagish Lake carbonaceous chondrite fall, along with bulk samples of the CI chondrite Orgueil and of several CM chondrites. Tagish Lake has a mean of refractory lithophile element/Cr ratios like those of CM chondrites, and distinctly higher than the CI chondrite mean. Tagish Lake exhibits abundances of the moderately volatile lithophile elements Na and K that are slightly higher than those of mean CM chondrites. Refractory through moderately volatile siderophile element abundances in Tagish Lake are like those of CM chondrites. Tagish Lake is distinct from CM chondrites in abundances of the most volatile elements. Mean CI‐normalized Se/Co, Zn/Co and Cs/Co for Tagish Lake are 0.68 ± 0.01, 0.71 ± 0.07 and 0.76 ± 0.02, while for all available CM chondrite determinations, these ratios lie between 0.31 and 0.61, between 0.32 and 0.58, and between 0.39 and 0.74, respectively. Considering petrography, and oxygen isotopic and elemental compositions, Tagish Lake is an ungrouped member of the carbonaceous chondrite clan. The overall abundance pattern is similar to those of CM chondrites, indicating that Tagish Lake and CMs experienced very similar nebular fractionations.

Bells is a CM chondrite with unusual petrologic characteristics. Bells has a mean CI‐normalized refractory lithophile element/Cr ratio of 0.96, lower than for any other CM chondrite, but shows CI‐normalized moderately volatile lithophile element/Cr ratios within the ranges of other CM chondrites, except for Na which is low. Iridium, Co, Ni and Fe abundances are like those of CM chondrites, but the moderately volatile siderophile elements, Au, As and Sb, have abundances below the ranges for CM chondrites. Abundances of the moderately volatile elements Se and Zn of Bells are within the CM ranges. Bells is best classified as an anomalous CM chondrite.
Mineralogy of Tagish Lake: An ungrouped type 2 carbonaceous chondrite
Authors: Zolensky M. E. , Nakamura K. , Gounelle M. , Mikouchi T. , Kasama T. , Tachikawa O. , Tonui E.
Published: January 2010

Abstract— In this paper we describe the recovery, handling and preliminary mineralogical investigation of the Tagish Lake meteorite. Tagish Lake is a type 2 carbonaceous chondrite which bears similarities to CI1 and CM chondrite groups, but is distinct from both. Abundant phyllosilicates as well as chondrules (however sparse) and common olivine grains in the matrix preclude any other classification. The bulk density of Tagish Lake (1.67 g/cc) is far lower than CI or CM chondrites (2.2‐2.3 and 2.6‐2.9 g/cc, respectively), or any other meteorite for that matter. We have identified two lithologies: a dominant carbonate‐poor lithology and a less‐abundant carbonate‐rich lithology. The meteorite is a breccia at all scales.

We have noted similarities between Tagish Lake and some clasts within the enigmatic meteorite Kaidun; possibly there are genetic relationships here worth exploring. In the paper we describe a clast of CM1 material within Tagish Lake which is very similar to a major lithology in Kaidun.
Thermal decomposition pattern and particle size estimation of iron minerals associated with the Cretaceous‐Tertiary boundary at Gubbio
Authors: Verma H. C. , Upadhyay C. , Tripathi A. , Tripathi R. P. , Bhandari N.
Published: January 2010

Abstract— Mössbauer studies of the samples from the Cretaceous‐Tertiary (K‐T) boundary layer at Gubbio, Italy show that iron appears mainly in two phases, magnetically ordered hematite and a paramagnetic silicate phase. The average particle size of hematite is estimated to be in the range of 16 to 27 nm from transmission electron micrographs and lack of a Morin transition. The hyperfine magnetic field at the iron nucleus is observed to be somewhat less than that of bulk hematite, which may be explained by collective magnetic excitation. Stepwise heating up to 1000°C shows a decomposition pattern of the paramagnetic phase, which suggests it to be a tri‐octahedral layer silicate. The iron‐bearing phases found in the bulk sedimentary K‐T boundary material are different from those found in the spherules separated from this material indicating that the redox conditions changed rapidly after the impact, becoming more oxidizing during the period these bulk phases were formed.
The oxygen isotopic composition of water from Tagish Lake: Its relationship to low‐temperature phases and to other carbonaceous chondrites
Authors: Baker L. , Franchi I. A. , Wright I. P. , Pillinger C. T.
Published: January 2010

Abstract— The fall and recovery of the Tagish Lake meteorite in British Columbia in January 2000 provided a unique opportunity to study relatively pristine samples of carbonaceous chondrite material. Measurements of the oxygen isotopic composition of water extracted under stepped pyrolysis from a bulk sample of this meteorite have allowed us to make comparisons with similar data obtained from CI and CM chondrites and so further investigate any relationships that may exist between these meteorites. The much lower yield of water bearing a terrestrial signature in Tagish Lake is indicative of the pristine nature of the meteorite. The relationship between the isotopic composition of this water and reported isotopic values for carbonates, bulk matrix and whole rock have been used to infer the extent and conditions under which parent‐body aqueous alteration occurred. In Tagish Lake the difference in Δ17O isotopic composition between the water and other phases is greater than that found in either CM or CI chondrites suggesting that reaction and isotopic exchange between components was more limited. This in turn suggests that in the case of Tagish Lake conditions during the processes of aqueous alteration on the parent body, which ultimately controlled the formation of new minerals, were distinct from those on both CI and CM parent bodies.
An experimental and petrographic investigation of Elephant Moraine 79001 lithology A: Implications for its petrogenesis and the partitioning of chromium and vanadium in a martian basalt
Authors: Herd Christopher D. K. , Schwandt Craig S. , Jones John H. , Papike James J.
Published: January 2010

Abstract— A composition approximating the lithology A groundmass of the Elephant Moraine (EET) 79001 martian basalt (Eg; McSween and Jarosewich, 1983) has been used to investigate the petrogenesis of the meteorite and the behavior of Cr and V at different oxygen fugacities. Crystallization experiments were carried out over a range of temperatures, and oxygen fugacities of either iron‐wüstite (IW) or IW + 2 (i.e., 1.5 log units below the quartz‐fayalite‐magnetite (QFM) buffer). Comparison of trace element concentrations (obtained by secondary ion mass spectrometry (SIMS) analysis) in experimental silicates with those of natural silicates supports the Fe‐Ti oxide‐derived oxygen fugacity of QFM −1.8 ± 0.3 for this basalt (Herd et al., 2001). Experimental distribution coefficients, in conjunction with SIMS analyses of rims from the olivine and pyroxene xenocrysts in lithology A, as well as analyses of lithology A groundmass pigeonite cores, are used to calculate coexisting liquid concentrations of V and Cr. Liquid compositions derived from pigeonite xenocryst rims and groundmass pigeonite cores are similar, suggesting that the rims of orthopyroxene xenocrysts are overgrowths, which have not previously been accounted for when reconstructing the groundmass composition. This implies that the Eg composition requires modification. A similar exercise for the ferroan rims on olivine xenocrysts yields very different liquid compositions, indicating that these rims are not overgrowths but are part of the xenocryst assemblage. These results are shown to be consistent with the petrography of lithology A xenocrysts.
Aluminum‐26 in H4 chondrites: Implications for its production and its usefulness as a fine‐scale chronometer for early solar system events
Authors: Zinner Ernst , Göpel Christa
Published: January 2010

Abstract— In order to investigate whether or not 26Al can be used as a fine‐scale chronometer for early solar system events we measured, with an ion microprobe, Mg isotopes and Al/Mg ratios in separated plagioclase, olivine, and pyroxene crystals from the H4 chondrites Ste Marguerite (SM), Forest Vale (FV), Beaver Creek and Quenggouk and compared the results with the canonical 26Al/27Al ratio for calcium‐aluminum‐rich inclusions (CAIs). For SM and FV, Pb/Pb and Mn‐Cr ages have previously been determined (Göpel et al., 1994; Polnau et al., 2000; Polnau and Lugmair, 2001). Plagioclase grains from these two meteorites show clear excesses of 26Mg. The 26Al/27Al ratios inferred from these excesses and from isotopically normal Mg in pyroxene and olivine are (2.87 ± 0.64) × 10−7 for SM and (1.52 ± 0.52) × 10−7 for FV. The differences between these ratios and the ratio of 5 times 10−5 in CAIs indicate time differences of 5.4 ± 0.1 Ma and 6.1 ± 0.2 Ma for SM and FV, respectively. These differences are in agreement with the absolute Pb/Pb ages for CAIs and SM and FV phosphates but there are large discrepancies between the U‐Pb and Mn‐Cr system for the relative ages for CAIs, SM and FV. For example, Mn‐Cr ages of carbonates from Kaidun are older than the Pb/Pb age of CAIs. However, even if we require that CAIs are older than these carbonates, the time difference between this “adjusted” CAI age and the Mn‐Cr ages of SM and FV require that 26 Al was widely distributed in the early solar system at the time of CAI formation and was not mostly present in CAIs, a feature of the X‐wind model proposed by Shu and collaborators (Gounelle et al., 2001; Shu et al., 2001). From this we conclude that there was enough 26Al to melt small planetary bodies as long as they formed within 2 Ma of CAIs, and that 26Al can serve as a fine‐scale chronometer for early solar system events.
Measuring the plasma environment at Mercury: The fast imaging plasma spectrometer
Authors: KOEHN P. L. , ZURBUCHEN T. H. , GLOECKLER G. , LUNDGREN R. A. , FISK L. A.
Published: January 2010

Abstract—The plasma environment at Mercury is a rich laboratory for studying the interaction of the solar wind with a planet. Three primary populations of ions exist at Mercury: solar wind, magnetospheric, and pickup ions. These pickup ions are generated through the ionization of Mercury's exosphere or are sputtered particles from the Mercury surface. A comprehensive mission to Mercury, such as MESSENGER (MErcury: Surface, Space ENvironment, GEochemistry, Ranging), should include a sensor that is able to determine the dynamical properties and composition of all these plasma components. An instrument to measure the composition of these ion populations and their three‐dimensional velocity distribution functions must be lightweight, fast, and have a very large field of view.

The fast imaging plasma spectrometer (FIPS) is an imaging mass spectrometer, part of NASA's MESSENGER mission, the first Mercury orbiter. This versatile instrument has a very small footprint, and has a mass that is ˜1 order of magnitude less than other comparable systems. It maintains a nearly full‐hemisphere field of view, suitable for either spinning or three‐axis‐stabilized platforms. The major piece of innovation to enable this sensor is a new deflection system geometry that enables a large instantaneous (˜1.5π) field of view. This novel electrostatic analyzer system is then combined with a position sensitive time‐of‐flight system. We discuss the design and prototype tests of the FIPS deflection system and show how this system is expected to address one key problem in Mercury science, that of the nature of the radar‐bright regions at the Hermean poles.
Crustal properties of Mercury by morphometric analysis of multi‐ring basins on the Moon and Mars
Authors: POTTS Laramie V. , von FRESE Ralph R. B. , SHUM C. K.
Published: January 2010

Abstract—We use satellite altitude free‐air and terrain gravity correlations to differentiate regional variations in crustal viscosity and transient cavity diameters of impact basins on the Moon and Mars that we combine with surface roughness for a rheological assessment of the crust of Mercury. For the Moon and Mars, we separate the free‐air anomalies into terrain‐correlated and terrain‐decorrelated components using the spectral properties of the free‐air and computed terrain gravity effects. Adjusting the terrain effects for the terrain‐correlated anomalies yields compensated terrain effects that we evaluate for crustal thickness variations of the impact basins. We interpret the terrain‐correlated anomalies for uncompensated elements of the crustal thickness variations that we find are strongly correlated with the distribution of basin rings from photogeologic analyses. Hence, we estimate the transient cavity diameter from the innermost diameter of the gravity‐inferred rings. Comparing these diameters with the related crustal thickness estimates clearly differentiates regional variations in the crustal rheologies. For the Moon, the analysis points to a farside crust that was significantly more rigid than the nearside crust during bombardment time. For Mars, the growth in transient cavity diameters with apparent crustal age also reflects increased viscosity due to crustal cooling. These results are also consistent with local estimates of surface roughness developed from the root‐mean‐squared topography over 64 times 64° patches centered on the basins. Hence for Mercury where gravity observations are lacking, rheological inferences on its crust may result from comparing photometric estimates of transient cavity diameter and local surface roughness with the lunar and martian estimates. These results for the Beethoven Basin, a typical multi‐ring impact feature of Mercury, suggest that the viscosity of the mercurian crust was relatively great during bombardment time. This enhanced rigidity, despite crustal temperatures that were probably much hotter than those of the Moon and Mars, may reflect an extremely dry crust for Mercury in its early development.
Lunar pure anorthosite as a spectral analog for Mercury
Authors: BLEWETT David T. , HAWKE B. Ray , LUCEY Paul G.
Published: January 2010

Abstract—Plans are underway for spacecraft missions to the planet Mercury beginning in the latter part of this decade (NASA's MESSENGER (MErcury, Surface, Space ENvironment, GEochemistry, Ranging) and ESA's BepiColombo). Mercury is an airless body whose surface is apparently very low in ferrous iron. Much of the mercurian surface material is expected to be optically mature, a state produced by the “space weathering” process from direct exposure to the space environment. If appropriate analog terrains can be identified on the Moon, then study of their reflectance spectra and composition will improve our understanding of space weathering of low‐Fe surfaces and aid in the interpretation of data returned from Mercury by the spacecraft.

We have conducted a search for areas of the lunar surface that are optically mature and have very low ferrous iron content using Clementine ultraviolet‐visible (UV‐vis) image products. Several regions with these properties have been identified on the farside. These areas, representing mature pure anorthosites (>90% plagioclase feldspar), are of interest because only relatively immature pure anorthosites have previously been studied with Earth‐based spectrometry. A comparison of Mercury with the lunar analogs reveals similarities in spectral characteristics, and there are hints that the mercurian surface may be even lower in FeO content than the lunar pure anorthosites.

We also investigate the potential for use of spectral features other than the commonly studied “1 μm” mafic mineral absorption band as tools for compositional assessment when spacecraft spectral measurements of Mercury become available. Most low‐Fe minerals plausibly present on Mercury lack absorption bands, but plagioclase possesses an iron impurity absorption at 1.25 μm. Detection of this diagnostic band may be possible in fresh crater deposits.
A procedure for determining the nature of Mercury's core
Authors: PEALE Stanton J. , PHILLIPS Roger J. , SOLOMON Sean C. , SMITH David E. , ZUBER Maria T.
Published: January 2010

Abstract— We review the assertion that the precise measurement of the second degree gravitational harmonic coefficients, the obliquity, and the amplitude of the physical libration in longitude, C20, C22, θ, and φ0, for Mercury are sufficient to determine whether or not Mercury has a molten core (Peale, 1976). The conditions for detecting the signature of the molten core are that such a core not follow the 88‐day physical libration of the mantle induced by periodic solar torques, but that it does follow the 250 000‐year precession of the spin axis that tracks the orbit precession within a Cassini spin state. These conditions are easily satisfied if the coupling between the liquid core and solid mantle is viscous in nature. The alternative coupling mechanisms of pressure forces on irregularities in the core‐mantle boundary (CMB), gravitational torques between an axially asymmetric mantle and an assumed axially asymmetric solid inner core, and magnetic coupling between the conducting molten core and a conducting layer in the mantle at the CMB are shown for a reasonable range of assumptions not to frustrate the first condition while making the second condition more secure. Simulations have shown that the combination of spacecraft tracking and laser altimetry during the planned MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, Ranging) orbiter mission to Mercury will determine C20, C22, and θ to better than 1% and φ0 to better than 8%—sufficient precision to distinguish a molten core and constrain its size. The possible determination of the latter two parameters to 1% or less with Earth‐based radar experiments and MESSENGER determination of C20 and C22 to 0.1% would lead to a maximum uncertainty in the ratio of the moment of inertia of the mantle to that of the whole planet, Cm/C, of ˜2% with comparable precision in characterizing the extent of the molten core.
One meteorite less from Vietnam
Authors: ROCHETTE P.
Published: January 2010

Abstract— Among the four declared meteorites from Vietnam, the two most recent ones—Phuoc‐Binh (1941) and Fuc Bin (1971)—appear to be the same, following a visit to the Hanoi museum and an analysis of the literature. Phuoc‐Binh (L5) with a fall date of 1941 July 18 should be the correct entry.
Oral histories in meteoritics and planetary science: V. Brian Mason
Authors: Marvin Ursula B.
Published: January 2010

Abstract— In this interview, Brian Mason describes the sudden awakening of his interest in meteorites during his student days at Canterbury College in New Zealand when he read a paper on the cosmic abundances of the elements by Victor M. Goldschmidt. Subsequently, he won a scholarship for graduate study abroad and wrote to Goldschmidt asking if he could do a thesis with him in Norway. Shortly after he began his research in Oslo, he fled the city, ahead of the German invasion of Norway, and completed his doctorate in Stockholm with a thesis on the iron‐manganese minerals of the Långban Mine. After the war he taught for 3 years at Canterbury College where he gave courses on mineralogy and geology (into which he inserted lectures on geochemistry) and led students in extensive field studies. In 1947, Mason accepted a professorship of mineralogy at Indiana University. While there, he wrote the landmark book, Principles of Geochemistry, which appeared in 1952. The following year he moved to New York City where he served as the Curator of Minerals at the American Museum of Natural History and an adjunct professor at Columbia University. He became fascinated with the museum's meteorite collection and discussed meteorites in his lectures, which inspired some of his outstanding students to enter the field. During a sabbatical year he spent as a Fulbright Professor in Japan, he gave an advanced level seminar on meteorites and based his book, Meteorites, on his lecture notes. Mason developed a rapid method of optically classifying chondritic meteorites that he applied to major collections in many countries, thus enabling curators to replace uninformative labels such as “stone” or “chondrite” with species names, and to recognize which of their meteorites were rare types demanding serious study. In 1965 he moved to the Smithsonian Institution in Washington, D.C. where he remained for the rest of his career. Early in 1968, he collected specimens from the spectacular fall of the Allende meteorite in Mexico, which proved to be a carbonaceous chondrite containing rare types of inclusions enriched in calcium and aluminum. His analyses showed how these inclusions could be divided into groups on the basis of their differing rare earth element patterns. Mason's studies of Allende continued while he investigated lunar samples returned by the Apollo missions and coauthored a book on them. Beginning in the latter 1970s, he applied his rapid classification of stony meteorites to the large numbers of specimens collected each year by U.S. teams on the Antarctic ice sheet. In 1992 he capped his career with a biography of Victor M. Goldschmidt. In recognition of his many fundamental contributions, The Meteoritical Society honored Brian Mason with its Leonard Medal at its meeting in 1972 at the University of Chicago.
Oral histories in meteoritics and planetary science: VI. Stuart Ross Taylor
Authors: MARVIN Ursula B.
Published: January 2010

Abstract— In this interview, Ross Taylor describes how his interest in planetary science was aroused by proofreading Brian Mason's book on geochemistry. Born and raised in New Zealand, Ross majored in chemistry at Canterbury College in Christchurch. While there, he took a course in geology and was strongly tempted to change his major, but he resolved the problem by becoming a geochemist. For his doctoral studies, Ross joined Mason at Indiana University where he learned the basics of trace element analysis on the emission spectrograph. Subsequently, he set up emission spectrographic laboratories and used them to pursue his research at Oxford University and the University of Cape Town. As techniques became more sensitive, he set up a spark‐source mass spectrograph at the Australian National University in Canberra. Ross always has retained an interest in terrestrial rocks, but he is most widely known for his investigations of tektites and lunar rocks. He became one of the earliest and strongest advocates of tektites as molten terrestrial sediments sent aloft by high‐energy impacts. As a member of the preliminary examination team that analyzed the samples returned by the Apollo missions, Ross gained an intimate knowledge of lunar chemistry and petrology and wrote three books about the Moon. He also has written a book about the chemical evolution of the solar system, a topic on which such rapid progress was made in 10 years that his second edition is practically a different book from the first one. Ross has written Destiny or Chance, a philosophical consideration of the likelihood that as sentient beings we may well be alone in the universe. Ross served as the president of The Meteoritical Society in 1989 and 1990, and at its annual meeting in Dublin, Ireland, in 1998, the Society presented him with its Leonard Medal.
Oral histories in meteoritics and planetary science: VII. Alastair G. W. Cameron
Authors: MARVIN Ursula B.
Published: January 2010

Abstract— In this interview, Alastair Cameron recounts how he started his career as a nuclear physicist but taught himself astrophysics after he read a paper that required an astrophysical explanation for the presence of technetium in red giant stars. Subsequently, as new analytical data became available, he periodically updated the Suess‐Urey tables of elemental abundances to enhance the value of the systematic approach they provided to understanding individual processes of nucleosysthesis. Since many of these new data were based on analyses of carbonacous chondrites, he taught himself meteoritics. In recent decades, Cameron has focused his research interests on problems such as the provenance of certain components of meteorites (calcium‐aluminum‐rich inclusions, FUN (fractionated and unknown nuclear) anomalous inclusions, amoeboid olivine aggregates, and presolar grains) that he believes to have formed in the supernova envelope prior to formation of the solar nebula, the origin of chondrules in the primitive solar nebula, and the origins of the solar system and of the Earth‐Moon system. To investigate these subjects he has pioneered the use of advanced computer technology to make lengthy calculations of nucleosysthesis in complicated networks. After teaching courses and advising graduate students at several research institutes and colleges, Cameron served as a Professor of Astronomy at Harvard University from 1973 to 1997 when he was appointed to the Donald H. Menzel Research Professorship of Astrophysics. In 1994, The Meteoritical Society honored him with the Leonard Medal at its meeting in Prague, the Czech Republic.
Oral histories in meteoritics and planetary science: VIII. Friedrich Begemann
Authors: MARVIN Ursula B.
Published: January 2010

Abstract— In this interview, taped in 2001 during The Meteoritical Society meeting in Rome, Friedrich Begemann recalls that after he earned his doctorate in physics under the direction of Professor Friedrich G. Houtermans, first in Göttingen and then in Bern, Switzerland, he began his career as what he calls a low‐level gas counting man, specializing in tritium (3H). In 1954 he accepted an invitation from Professor Willard F. Libby to run his gas‐counting laboratory at the University of Chicago. Begemann spent 3 years there during which he traced the distribution in the world's atmosphere and waters of tritium from two sources, natural cosmic radiation and the detonation of the first thermonuclear device. During his time at Chicago he was drawn into Harold C. Urey's group of scientists studying meteorites. Begemann found that he could measure tritium in meteorites, and by coupling his values with those of 3He, he and his collaborators initiated a new branch of meteoritics by determining the first cosmic‐ray exposure age of a meteorite—Norton County, which fell in 1947. In 1957, Begemann joined the group led by Friedrich A. Paneth at the Max‐Planck‐Institut für Chemie at Mainz, Germany, where he continued his studies of gas isotopes for the remainder of his career. His research led to the discovery of primitive noble gases in the diamond—graphite aggregates in ureilites, where their presence in presumably deep‐seated igneous rocks still remains to be explained. With the advent of the Apollo missions, Begemann extended his studies to the lunar rocks and soils in an effort to learn as much as possible about the interaction of solids with the space environment. He also became heavily involved in measuring the s‐process isotope abundance patterns of medium‐heavy chemical elements as they occur in interstellar grains. In 1995 at the meeting in Washington, D.C., The Meteoritical Society presented Friedrich Begemann with the Leonard Medal for his contributions to our understanding of the radiation encountered by bodies as they orbit through space.