bluuebunny/crossref_metadata_2025 huggingface dataset:
Collateral consequences of the inhomogeneous distribution of short‐lived radionuclides in the solar nebula
Authors: NICHOLS Robert H. , PODOSEK Frank A. , MEYER Brad S. , JENNINGS Cristine L.
Published: February 2010

Abstract— The presence of several short‐lived (now extinct) radionuclides in the early solar system demands that they were synthesized and added to preexisting solar system materials shortly (on a time scale on the order of the relevant radionuclide lifetime) before formation of solar system solids. For diverse reasons, it is often suggested that the solar system distributions of these radionuclides were radically heterogeneous, perhaps because of the late addition. Much attention has been given to the astrophysical circumstances that might govern the synthesis and distribution of these short‐lived radionuclides, but comparatively little attention has been devoted to the distribution of cosynthesized isotopes. The focus of this paper is a systematic, quantitative evaluation of the collateral consequences in stable and long‐lived isotopes that might be expected if short‐lived radionuclides, in particular 26Al or 53Mn, were injected at their canonical levels and inhomogeneously distributed in the early solar system. We mix model massive star yields of Meyer et al. (1995) and Woosley and Weaver (1995) into a reservoir of cosmic composition, as tabulated by Anders and Grevesse (1989). To mitigate the effects of systematic deviations that may be present in these mixtures due to uncertainties in model stellar yields, we follow Timmes and Clayton (1996) and also mix into a “renormalized” proxy solar system composition computed from a galactic chemical evolution model based primarily on the stellar yields of Woosley and Weaver (1995). The results are very unfavorable to the likelihood of heterogeneously distributed 26Al derived from supernova ejecta. If a massive star is invoked to account for 26Al, its ejecta must have been rather uniformly distributed, as inferred from the lack of measured collateral anomalies in several elements, notably Ca, Cr, and Ni. Conversely, if 26Al were indeed radically heterogeneously distributed, some other nucleosynthetic source more efficient at producing 26Al is required. In principle, a similar statement applies to 53Mn, but the situation is more complicated. The inferred anomalies at 53Cr will depend not only on how much 53Mn is added by a heterogeneous component, but also more sensitively on the contributions to the associated stable nuclides, 53Cr, 52Cr, and 50Cr. Consideration of predicted collateral anomalies provides no direct support for heterogeneously distributed supernova‐derived 53Mn, but the required quantity of supernova contribution, and thus also the collateral anomalies, are much less for 53Mn than for 26Al. With allowance for model calculation uncertainties, it could be argued that anomalies collateral to heterogeneous 53Mn might be small enough to have evaded detection.
First results from video spectroscopy of 1998 Leonid meteors
Authors: BOROVICKA J. , STORK R. , BOCEK J.
Published: February 2010

Abstract— We report spectroscopic observations of meteors made from the FISTA aircraft on 1998 November 17 as a part of the Leonid multi‐instrument aircraft campaign. Low‐resolution spectra of 119 meteors of apparent visual magnitudes from +3 to −4, corresponding to meteoroid masses from 10−6 to 10−3 kg, were obtained. After analyzing a representative sample of the spectra and comparing them to the spectra of Perseid meteors from the Ondrejov archive, the following conclusions were reached: Leonid meteoroids are very loose and disintegrate easily in the atmosphere. This leads to much faster evaporation of volatile Na than of other elements, an effect which is not observed in the Perseid meteors. Relative bulk abundances of Mg, Fe, Ca, and Na in Leonid meteors are nearly CI‐chondritic within the uncertainty of the method (factor of 3). Smaller meteoroids tend to be poorer in Na, which is true also for Perseid meteors. Most meteoric vapor emissions could be reasonably well explained with the temperature of 4500 K. High‐temperature meteoric emissions (Ca+, Mg+) are present only in bright meteors. Leonid spectra are very rich in atmospheric emissions of O, N, and N2, even at high altitudes and in faint meteors. These emissions are therefore not connected with the meteor shock wave. Thermal continuum is also present in the spectra. Organic material was not revealed.
Iron, calcium, and potassium atom densities in the trails of Leonids and other meteors: Strong evidence for differential ablation
Authors: von ZAHN U. , GERDING M. , HÖFFNER J. , McNEIL W. J. , MURAD Edmond
Published: February 2010

Abstract— We report on studies of the Fe, Ca, and K atom densities in the trails of meteors. The measurements of the densities were taken simultaneously and in a common volume by three ground‐based lidars. We report and analyze the data obtained during two nights of Leonid showers (1996 and 1998 November 16/17) and of one night five days after the 1998 Leonids. The lidar‐observed trails of Leonids differ from those of other meteor showers in both their mean altitude and in mean metal composition. The Leonid trails show a highly depressed Ca/Fe abundance ratio in comparison to CI meteoritic composition.

Our observations are interpreted with the help of a numerical model that describes the ablation processes occurring during the high‐speed entry of meteoroids into the Earth's atmosphere. We conclude that for the lidar‐observed meteoroids, the ablation process occurs differentially for the three elements. This leads to a mixture of metals in the meteor trails, the composition of which is strongly altitude dependent and at any one altitude deviates significantly from a CI meteoritic composition. The model predicts differing altitudes and durations of trail observations for different showers, allowing us to tentatively assign the origin to the observed trails.
Origin of a unique impact‐melt rock—the L‐chondrite Ramsdorf
Authors: YAMAGUCHI Akira , SCOTT Edward R. D. , KEIL Klaus
Published: February 2010

Abstract— We have studied a unique impact‐melt rock, the Ramsdorf L chondrite, using optical and scanning microscopy and electron microprobe analysis. Ramsdorf contains not only clast‐poor impact melt (Begemann and Wlotzka, 1969) but also a chondritic portion (>60 g) with what appears at low magnification to be a normal, well‐defined chondritic texture. However, detailed studies at high magnification show that >90 vol% of the crystals in the chondritic portion were largely melted by the impact: the chondrules lack normal microtextures and are ghosts of the original features. The only relics from the precursor chondrules are olivine crystals, which have the highest melting temperature (∼1620 °C). Pyroxene‐rich chondrules were so extensively melted that no phenocrysts were preserved and the melt crystallized in situ before significant mixing with exterior olivine‐rich melts. Fine‐grained pyroxene chondrule ghosts have sharper boundaries with the matrix than porphyritic olivine and pyroxene chondrule ghosts, probably because pyroxene‐rich melts are significantly more viscous. Complex textures that formed by injection of melt along cracks and fractures in relic olivines suggest that the chondritic portion of Ramsdorf formed directly from petrologic type 3–4 material by strong shock. We infer that Ramsdorf was largely melted by shock pressures of ∼75–90 GPa and that chondrule ghosts and relic olivine phenocrysts were locally preserved by rapid cooling. Quenching was not due to the addition of cold clasts into the melt but to heterogeneous shock heating that only caused internal melting of large olivines and pyroxenes. Ramsdorf appears to be one of the most heavily shocked meteorites that has retained some trace of its original texture.
Investigation of the Rhabdite/Kamacite Law of Intergrowth in iron meteorites with the aid of the Kossel technique
Authors: HENNIG C. , GEIST V. , HEIDE G.
Published: February 2010

Abstract— X‐ray microdiffraction measurements based on the Kossel effect have been used for orientation determinations of rhabdite (i.e., small prismatic schreibersite crystals) with respect to the kamacite matrix. For that purpose, polished specimens of the Toluca meteorite have been analyzed after surface etching. Kossel patterns of kamacite and rhabdite have been recorded and simulated. As the law of intergrowth for idiomorphic rhabdite crystals, we confirmed the relations:

In comparison with typical line widths, the Kossel lines of kamacite are distinctly broadened. This is found for the meteorite Toluca and a for a second sample, the meteorite Morasko. This behaviour is probably connected with a high dislocation density, as shown by transmission electron microscope investigations.
Mineralogy, petrography, bulk chemical, iodine‐xenon, and oxygen‐isotopic compositions of dark inclusions in the reduced CV3 chondrite Efremovka
Authors: KROT A. N. , BREARLEY A. J. , ULYANOV A. A. , BIRYUKOV V. V. , SWINDLE T. D. , KEIL K. , MITTLEFEHLDT D. W. , SCOTT E. R. D. , CLAYTON R. N. , MAYEDA T. K.
Published: February 2010

Abstract— We studied the petrography, mineralogy, bulk chemical, I‐Xe, and O‐isotopic compositions of three dark inclusions (E39, E53, and E80) in the reduced CV3 chondrite Efremovka. They consist of chondrules, calcium‐aluminum‐rich inclusions (CAIs), and fine‐grained matrix. Primary minerals in chondrules and CAIs are pseudomorphed to various degrees by a mixture largely composed of abundant (>95%), fine‐grained (>0.2 μm) fayalitic olivine (Fa35–42) and minor amounts of chlorite, poorly‐crystalline Si‐Al‐rich material, and chromite; chondrule and CAI shapes and textures are well‐preserved. Secondary Ca‐rich minerals (Ti‐andradite, kirschsteinite, Fe‐diopside) are common in chondrule pseudomorphs and matrices in E39 and E80. The degree of replacement increases from E53 to E39 to E80. Fayalitic olivines are heavily strained and contain abundant voids similar to those in incompletely dehydrated phyllosilicates in metamorphosed CM and CI chondrites. Opaque nodules in chondrules consist of Ni‐ and Co‐rich taenite, Co‐rich kamacite, and wairauite; sulfides are rare; magnetite is absent. Bulk O‐isotopic compositions of E39 and E53 plot in the field of aqueously altered CM chondrites, close to the terrestrial fractionation line; the more heavily altered E39 is isotopically heavier than the less altered E53. The apparent I‐Xe age of E53 is 5.4 Ma earlier than Bjurböle and 5.7 ± 2.0 Ma earlier than E39. The I‐Xe data are consistent with the most heavily altered dark inclusion, E39 having experienced either longer or later alteration than E53. Bulk lithophile elements in E39 and E53 most closely match those of CO chondrites, except that Ca is depleted and K and As are enriched. Both inclusions are depleted in Se by factors of 3–5 compared to mean CO, CV, CR, or CK chondrites. Zinc in E39 is lower than the mean of any carbonaceous chondrite groups, but in E53 Zn is similar to the means in CO, CV, and CK chondrites.

The Efremovka dark inclusions experienced various degrees of aqueous alteration, followed by low degree thermal metamorphism in an asteroidal environment. These processes resulted in preferential oxidation of Fe from opaque nodules and formation of Ni‐ and Co‐rich metal, metasomatic alteration of primary minerals in chondrules and CAIs, and the formation of fayalitic olivine and secondary Ca‐Fe‐rich minerals. Based on the observed similarities of the alteration mineralization in the Efremovka and Allende dark inclusions, we infer that the latter may have experienced similar alteration processes.
“Pathological” Martian craters: Evidence for a transient obliteration event?
Authors: HARTMANN William K. , ESQUERDO Gilbert
Published: February 2010

Abstract— We have detected three unusual, low‐relief circular features, 1.2 to 2.1 km in diameter, in the northwest Noachis highlands, which may be craters that have undergone isostatic deformation. They may shed light on the existence, nature, and timing of suspected widespread Martian erosion/obliteration events, and offer clues to a type of Martian terrain softening. In the surrounding area, we find an anomalous deficiency of craters in the 3–11 km diameter range and evidence that larger, older craters have undergone relief softening and infill. We discuss three different hypotheses to explain these features, two of which involve Martian ice. This region may have undergone a transient event in which a near‐surface permafrost layer (several hundred meters deep) underwent partial melting or softening. This would allow relaxation of kilometer‐scale craters and softening of larger craters. Crater data presented here suggest that this event happened some time in mid‐Martian history. Whether the event was regional or related to global‐scale events is uncertain, though it may represent a class of events that also happened in other Martian areas.
Martian cratering VI: Crater count isochrons and evidence for recent volcanism from Mars Global Surveyor
Authors: HARTMANN William K.
Published: February 2010

Abstract— This paper develops a methodology to establish absolute Martian ages by deriving isochrons on a plot of Martian impact crater density vs. crater diameter, calibrated by lunar crater/age data. The isochrons illustrated here are based on a Mars/Moon cratering ratio of 1.6 at constant size, but there is a factor of 2 to 4 uncertainty in this ratio and the consequent model ages. Martian crater diameter distributions are determined in several areas down to diameter D = 16–45 m; the shapes of the curves in young areas are found to be close to that of the predicted isochrons and close to the standard production function found by Neukum. The youngest areas studied here display the lunar‐like production function down to D ∼30 m, where saturation equilibrium sets in. Model crater retention ages of several volcanic units are found to be a few hundred million years or less, with estimated uncertainties ranging from a factor of 2 lower to a factor of 4 higher. The results are consistent with Martian meteorite ages. Volcanism on Mars has probably persisted into the last 10 to 15% of the planet's history and is likely ongoing. Because surfaces as young as a few hundred million years have reached crater saturation equilibrium at D < ∼60 to 100 m, Mars is likely to have widespread impact‐produced regoliths at least a few meters deep, and this may contribute to the widespread mobile dust and boulder fields of Mars.
Crystallization of magmatic iron meteorites: The role of mixing in the molten core
Authors: CHABOT Nancy L. , DRAKE Michael J.
Published: February 2010

Abstract—The IIIAB group is the largest of the magmatic iron meteorite groups and consequently is commonly used to test models of asteroid core crystallization. Simple fractional crystallization calculations appear to reproduce the general shape of the elemental trends observed in the IIIAB group when these trends are plotted vs. Ni, as is traditionally done. However, when the elemental trends are examinedvs.another element (such as Gevs.Ir), simple fractional crystallization fails to match a significant portion of the trend, specifically meteorites formed during the final stages of crystallization. Our simple mixing model, which attempts to account for the possibility of inhomogeneities in the molten metallic core, is able to reproduce the entire IIIAB trend observed. This model is a variant of simple fractional crystallization and involves mixing between a zone of liquid involved in the crystallization process and a second zone too far from the crystallizing solid to be actively involved in crystallization. This model does not suggest one unique solution for the method by which an asteroidal core crystallizes; rather it demonstrates that including the effects of mixing in the molten core can account for the observed IIIAB elemental trends, particularly the late‐stage crystallizing members, which other models have difficulty explaining.
The phosphates of IIIAB iron meteorites
Authors: OLSEN Edward J. , KRACHER Alfred , DAVIS Andrew M. , STEELE Ian M. , HUTCHEON Ian D. , BUNCH T. E.
Published: February 2010

Abstract— Thirteen phosphate minerals are found in IIIAB iron meteorites. Four of these (sarcopside, graftonite, johnsomervilleite, and galileiite) constitute the majority of occurrences. The IIIB iron meteorites are confined to occurrences of only these four phosphates. The IIIA iron meteorites may contain one or more of these four phases; they may also contain other rarer phosphates, and silica (in two instances) and a silicate rock (in one instance). Thus, the IIIA lithophile chemistry is more varied than that of the IIIB meteorites. Based on petrographic relations, sarcopside appears to be the first phosphate to form. Graftonite is probably formed by recrystallization of sarcopside. Johnsomervilleite and galileiite exsolved as enclaves in sarcopside or graftonite at lower temperatures, although some of these also nucleated as separate crystals. The IIIAB phosphates are carriers of a group of incompatible lithophile elements: Fe, Mn, Na, Ca, and K, and, rarely, Mg as well as Pb. These elements (and O) were concentrated in a residual, S‐rich liquid during igneous fractional crystallization of the IIIAB core mass. The phosphates formed by oxidation of P as the core solidified and excluded O, which increased its partial pressure in the residual liquid. The trace siderophile trends in bulk IIIAB metal are paralleled by a mineralogical trend of the phosphate minerals that formed. For IIIAB meteorites with low‐Ir contents in the metal, the phosphates are mainly Fe‐Mn phases; at intermediate Ir values, more Na‐bearing phosphates appear; at the highest Ir values, the rarer Na‐, K‐, Mg‐, Cr‐, and Pb‐bearing phosphates appear. The absence of significant amounts of Mg, Si, Al, and Ti suggest depletion of these elements in the core by the overlying mantle.
Aspects of the validation of magnetic remanence in meteorites
Authors: WASILEWSKI Peter , DICKINSON Tamara
Published: February 2010

Abstract— Meteorite magnetic records constitute physical evidence of processes acting during early solar system evolution. Consequently, the validation of these records is important in meteorite research. The first step in the validation process should be the REM value. The REM value is the ratio of natural remanence (NRM) to saturation remanent magnetization imparted by a 1 T magnetic field (SIRM). The REM values range over 3 to 4 orders of magnitude for stony meteorites and for chondrules from Allende (C3V‐S1), Bjurböle (L4‐S1), and Chainpur (LL3‐S1) meteorites.

The REM values computed from published NRM and SIRM data identify many orders of magnitude range in the REM values including REM values >100 × 10−3. These data suggest a dependence for the NRM intensity on the curatorial location from which the sample was obtained. Any earth rock acquiring thermoremanent magnetization (TRM) in the geomagnetic field has a restricted range in REM mostly between 5 and 50 × 10−3, the exception being the mineral hematite in the multidomain size range. The only terrestrial samples with REM much greater than 100 × 10−3 are those struck by lightning.

The REM value provides a physical basis for recognition between valid records and those that “might be contaminated.” The isothermal remanence acquisition (RA) curve is presented as a contamination curve that allows an indication of the level of magnetic field contamination required to give the computed “REM” (RM/SIRM) value. In the case of the Bjurböle and Chainpur chondrules, with REM values >100 × 10−3, the RA curve indicates that unrealistically large contamination magnetic fields would be required to give REM values greater than 100 × 10−3. This would suggest contamination other than by a hand magnet that is normally available to an experimenter. This would require an explanation that would involve large magnetic fields during chondrule formation, or some extraordinary remanence acquisition mechanism that remains to be described.

Magnetic contamination experiments, using ∼80 and ∼40 mT magnets, demonstrate that the “REM” values and extent of modification of the magnetic vector record are mineralogy dependent, and this is mostly related to the amount and characteristics of the mineral tetrataenite. The complexity of the meteorite records suggest validation of the record as a first step. The REM value is the first physical statement that can be made in this validation.
Argon‐40/argon‐39 age of the El'gygytgyn impact event, Chukotka, Russia
Authors: LAYER Paul W.
Published: February 2010

Abstract— Lake El'gygytgyn, Chukotka, Russia, lies in a ∼18 km crater of presumably impact origin. The crater is sited in Cretaceous volcanic rocks of the Okhotsk‐Chukotka volcanic belt. Laser 40Ar/39Ar dating of impact‐melted volcanic rocks from the rim of Lake El'gygytgyn yields a 10‐sample weighted plateau age of 3.58 ± 0.04 Ma. The Ar step‐heating method was critical in this study in identifying inherited Ar in the samples due to incomplete degassing of the Cretaceous volcanic rocks during impact melting. This age is consistent with, but more precise than, previous K‐Ar and fission‐track ages and indicates an “instantaneous” formation of the crater. This tight age control, in conjunction with the presence of impactites, shocked quartz, and other features, is consistent with an impact origin for the structure and seems to discount internal (volcanogenic) origin models.
Petrology of the Indian eucrite Piplia Kalan
Authors: BUCHANAN P. C. , MITTLEFEHLDT D. W. , HUTCHISON R. , KOEBERL C. , LINDSTROM D. J. , PANDIT M. K.
Published: February 2010

Abstract— Piplia Kalan is an equilibrated eucrite consisting of 60–80 vol% lithic clasts in a subordinate brecciated matrix. Ophitic/subophitic clasts fall into two groups: finer‐grained lithology A and coarser‐grained lithology B. Very fine‐grained clasts with equigranular textures (lithology C) also occur and originally were hypocrystalline in texture. The variety of materials represented in Piplia Kalan suggests cooling histories ranging from quenching to slower crystallization. Despite textural differences, clasts and matrix have similar mineral and bulk compositions. Thus, Piplia Kalan is probably best classified as a genomict breccia that could represent fragments of a single lava flow or shallow intrusive body, including fine‐grained or glassy outer margin and more slowly cooled coarser‐grained interior. Bulk composition suggests that the meteorite is most closely related to the main group eucrites, but it probably was affected by minor amounts of fractional crystallization. Piplia Kalan displays evidence of an early shock event, including brecciated matrix and areas of lithic clasts that contain very fine‐grained, granular pyroxene between deformed feldspar laths. The meteorite also displays evidence of at least one episode of extensive thermal metamorphism: hypocrystalline materials are recrystallized to hornfelsic textures and minerals throughout the meteorite contain abundant inclusions that are relatively large in size. Veins of brown glass transect both clasts and matrix and indicate a second, postmetamorphism shock event.
Mineralogical and chemical composition and cosmic‐ray exposure history of two mesosiderites and two iron meteorites
Authors: TERRIBILINI Dario , EUGSTER Otto , MITTLEFEHLDT David W. , DIAMOND Larryn W. , VOGT Stephan , WANG Daode
Published: February 2010

Abstract—We performed a comprehensive study of the noble gas isotopic abundances, radionuclide activities, and mineralogical and chemical composition of two mesosiderites and two iron meteorites. For the mesosiderites Dong Ujimqin Qi and Weiyuan, the silicate and the metal phases were studied. The anomalous ataxite Rafrüti is not chemically related to any other meteorite class, whereas Ningbo is a type IVA octahedrite. The mineralogy and major and trace element abundances of the silicate phases of Dong Ujimqin Qi and Weiyuan are similar to those of other mesosiderites and distinct from those of the howardites. The cosmic‐ray exposure history was studied based on the concentrations of the cosmogenic noble gas nuclei and radionuclide activities. For the iron meteorites, cosmic‐ray exposure ages were calculated from the pairs10Be‐21Ne,26Al‐21Ne, and36Cl‐36Ar. Rafrüti yields the youngest exposure age of all ataxites (6.8 ± 1.7 Ma), whereas that of Ningbo with 107 ± 15 Ma falls within the range observed for the other octahedrites. The parent body break‐up times of the mesosiderites Dong Ujimqin Qi and Weiyuan are 252 ± 50 and 25.9 ± 5.0 Ma, respectively. We find no evidence for a common break‐up event for the mesosiderites and the howardites.
The oxygen‐isotopic record in enstatite meteorites
Authors: NEWTON J. , FRANCHI I. A. , PILLINGER C. T.
Published: February 2010

Abstract— Oxygen‐isotopic compositions were determined for a suite of enstatite chondrites and aubrites. In agreement with previous work (Clayton et al., 1984), most samples have O‐isotopic compositions close to the terrestrial fractionation line (TFL), and there appear to be no significant differences in O‐isotopic compositions between individual EH and EL chondrites and aubrites. Five enstatite meteorites have O‐isotopic compositions that are significantly different from the other samples and >0.2% away from the TFL. Two of these have petrographic evidence of brecciation and interaction between other meteorite types; for the other three, similar scenarios are suggested. There appears to be a systematic increase in δ18O from enstatite chondrites (both EH and EL) of petrologic type 3 to those of type 6. There is also good evidence that the EH meteorites do not fall along a mass fractionation line but along a line slope 0.66. At the present time, detailed understanding of the origin of these O‐isotopic systematics remain elusive but clearly point to a complex accretion history, parent‐body evolution, or both.
Water soluble ions in the Nakhla martian meteorite
Authors: SAWYER Douglas J. , McGEHEE Michael D. , CANEPA Julie , MOORE Carleton B.
Published: February 2010

Abstract—Water‐soluble ion concentrations from the martian achondrite Nakhla and three asteroidal achon drites are reported. The Nakhla sample contains significant concentrations of chloride, sulfate, Mg, Na, Ca, and K ions. The results are interpreted to indicate that this rock has been in contact with a seawater‐like brine on the martian surface.
The Vissannapeta eucrite
Authors: GHOSH S. , PANT N. C. , RAO T. K. , MOHANA C. RAMA , GHOSH J. B. , SHOME S. , BHANDARI N. , SHUKLA A. D. , SUTHAR K. M.
Published: February 2010

Abstract— A wholly encrusted single stone that fell in Vissannapeta, Andhra Pradesh, India has been identified as a cumulate eucrite based on its primary texture and mineral composition: anorthite(An92.4–94.6), orthopyroxene(En49.1–51.8Fs44.2–49.7Wo1.2–4.0), and clinopyroxene (En38.8–46.8Fs14.8–33.6Wo19.6–46.4). The stone is pyramidal in shape, and the crust shows rib‐like flow features indicating that it had an oriented passage through the atmosphere towards the terminal stage of its flight. Conditions of its fall, mineralogical characteristics, and results of measurements of cosmogenic radioactivity (26Al, 22Na, and 54Mn) and track density are described. Aluminum‐26 and 22Na in Vissannapeta are ∼75% of the expected values and also lower by a similar factor compared to the activities measured in Piplia Kalan, another eucrite, which fell ∼18 months before Vissannapeta. Because higher activity of 22Na and 54Mn would be expected from solar cycle modulation of galactic cosmic rays, these results, as well as the track density gradient, indicate that Vissannapeta was a small body (≤120 kg) in the interplanetary space wherein the nuclear cascade due to galactic cosmic rays did not develop fully. Tracks, surface morphology, and crustal features indicate at least two fragmentation events in the atmosphere.
Primordial noble gases in “phase Q” in carbonaceous and ordinary chondrites studied by closed‐system stepped etching
Authors: BUSEMANN Henner , BAUR Heinrich , WIELER Rainer
Published: February 2010

Abstract— The HF/HCI‐resistant residues of the chondrites CM2 Cold Bokkeveld, CV3 (ox.) Grosnaja, CO3.4 Lancé, CO3.7 Isna, LL3.4 Chainpur, and H3.7 Dimmitt have been measured by closed‐system stepped etching (CSSE) in order to better characterise the noble gases in “phase Q”, a major carrier of primordial noble gases. All isotopic ratios in phase Q of the different meteorites are quite uniform, except for (20Ne/22Ne)Q. As already suggested by precise earlier measurements (Schelhaas et al., 1990; Wieler et al., 1991, 1992), (20Ne/22Ne)Q is the least uniform isotopic ratio of the Q noble gases. The data cluster ∼10.1 for Cold Bokkeveld and Lancé and 10.7 for Chainpur, Grosnaja, and Dimmitt, respectively. No correlation of (20Ne/22Ne)Q with the classification or the alteration history of the meteorites has been found. The Ar, Kr, and Xe isotopic ratios for all six samples are identical within their uncertainties and similar to earlier Q determinations as well as to Ar‐Xe in ureilites. Thus, an unknown process probably accounts for the alteration of the originally incorporated Ne‐Q. The noble gas elemental compositions provide evidence that Q consists of at least two carbonaceous carrier phases “Q1” and “Q2” with slightly distinct chemical properties. Ratios (Ar/Xe)Q and (Kr/Xe)Q reflect both thermal metamorphism and aqueous alteration. These parent‐body processes have led to larger depletions of Ar and Kr relative to Xe. In contrast, meteorites that suffered severe aqueous alteration, such as the CM chondrites, do not show depletions of He and Ne relative to Ar but rather the highest (He/Ar)Q and (Ne/Ar)Q ratios. This suggests that Q1 is less susceptible to aqueous alteration than Q2. Both subphases may well have incorporated noble gases from the same reservoir, as indicated by the nearly constant, though very large, depletion of the lighter noble gases relative to solar abundances. However, the elemental ratios show that Q1 and Q2 must have acquired (or lost) noble gases in slightly different element proportions. Cold Bokkeveld suggests that Q1 may be related to presolar graphite. Phases Q1 and Q2 might be related to the subphases that have been suggested by Gros and Anders (1977). The distribution of the 20Ne/22Ne ratios cannot be attributed to the carriers Q1 and Q2. The residues of Chainpur and Cold Bokkeveld contain significant amounts of Ne‐E(L), and the data confirm the suggestion of Huss (1997) that the 22Ne‐E(L) content, and thus the presolar graphite abundances, are correlated with the metamorphic history of the meteorites.
Light noble gases and cosmogenic radionuclides in Estherville, Budulan, and other mesosiderites: Implications for exposure histories and production rates
Authors: ALBRECHT A. , SCHNABEL C. , VOGT S. , XUE S. , HERZOG G. F. , BEGEMANN F. , WEBER H. W. , MIDDLETON R. , FINK D. , KLEIN J.
Published: February 2010

Abstract—We report measurements of26AI,10Be,41Ca, and36Cl in the silicate and metal phases of 11 mesosiderites, including several specimens each of Budulan and Estherville, of the brecciated meteorite Bencubbin, and of the iron meteorite Udei Station. Average production rate ratios (atom/atom) for metal phase samples from Estherville and Budulan are26Al/10Be = 0.77 ± 0.02;36Cl/10Be = 5.3 ± 0.2. For a larger set of meteorites that includes iron meteorites and other mesosiderites, we find26Al/10Be = 0.72 ± 0.01 and36Cl/10Be = 4.5 ± 0.2. The average41Ca/36Cl production rate ratio is 1.10 ± 0.04 for metal separates from Estherville and four small iron falls. The41Ca activities in dpm/(kg Ca) of various silicate separates from Budulan and Estherville span nearly a factor of 4, from <400 to >1600, indicating preatmospheric radii of >30 cm. After allowance for composition, the activities of26Al and10Be (dpm/kg silicate) are similar to values measured in most ordinary chondrites and appear to depend only weakly on bulk Fe content. Unless shielding effects are larger than suggested by the36Cl and41Ca activities of the metal phases, matrix effects are unimportant for10Be and minor for26Al.

Noble gas concentrations and isotopic abundances are reported for samples of Barea, Emery, Mincy, Morristown, and Marjalahti. New estimates of36Cl/36Ar exposure ages for the metal phases agree well with published values. Neon‐21 production rates for mesosiderite silicates calculated from these ages and from measured21Ne contents are consistently higher than predicted for L chondrites despite the fact that the mesosiderite silicates have lower Mg contents than L chondrites. We suggest that the elevation of the21Ne production rate in mesosiderite silicates reflects a “matrix effect,” that is, the influence of the higher Fe content of mesosiderites, which acts to enhance the flux of low‐energy secondary particles and hence the21Ne production from Mg. As10Be production is relatively insensitive to this matrix effect,10Be/21Ne ages give erroneously low production rates and high exposure ages. By coincidence, standard22Ne/21Ne based “shielding” corrections give fairly reliable21Ne production rates in the mesosiderite silicates.
Lunar surface exposure models for meteorites Elephant Moraine 96008 and Dar al Gani 262 from the Moon
Authors: EUGSTER Otto , POLNAU Ernst , SALERNO Emma , TERRIBILINI Dario
Published: February 2010

Abstract— We derived the cosmic‐ray and solar particle exposure history for the two lunar meteorites Elephant Moraine (EET) 96008 and Dar al Gani (DaG) 262 on the basis of the noble gas isotopic abundances including the radionuclide 81Kr. For EET 96008, we propose a model for the exposure to cosmic rays and solar particles in three stages on the Moon: an early stage ∼500 Ma ago, lasting less than 9 Ma at a shallow shielding depth of 20 g/cm2, followed by a stage when the material was buried, without exposure, until it was exposed in a recent stage. This recent stage, at a shielding depth in a range of 200–600 g/cm2, lasted for ∼26 Ma until ejection. This model is essentially the same as that previously found for lunar meteorite EET 87521; thus, pairing of the two Elephant Moraine lunar meteorites that were recovered on the same icefield in Antarctica is confirmed by our data. The cosmic‐ray‐produced isotopes, the trapped solar and lunar atmospheric noble gases, as well as the radionuclide 81Kr observed for the DaG 262 lunar meteorite are consistent with a one‐stage lunar exposure history. The average burial depth of the Dar al Gani material before ejection was within a range of 50–80 g/cm2. The exposure to cosmic rays at this depth lasted 500–1000 Ma. This long residence time for Dar al Gani at relatively shallow depth explains the high concentrations of implanted solar noble gases.
Exposure history of the Mocs (L6) chondrite: A study of strewn field samples
Authors: FERKO T. E. , SCHULTZ L. , FRANKE L. , BOGARD D. D. , GARRISON D. H. , HUTCHISON R. , LIPSCHUTZ M. E.
Published: February 2010

Abstract— We measured cosmogenic radionuclides (10Be, 26Al, and 36Cl) and noble gases (He, Ne, and Ar) in 10 specimens of the Mocs L6 chondrite to determine the exposure history and preatmospheric relationship among fragments from known locations in the strewn field. Cosmogenic noble gas contents alone are consistent with a simple irradiation exposure of 15.2 Ma. However, Mocs has very low 22Ne/21Ne ratios indicative of deep burial in a large meteoroid, but radionuclide levels at saturation values typical for much smaller meteoroids: this paradox suggests a possible complex exposure. For the latter case, we propose a two‐stage exposure history in which Mocs initially was deeply buried in a large object for 110 Ma, followed by exposure in a 65 cm object for 10.5 Ma. Relative shielding was inferred from the measured 22Ne/21Ne ratios assuming constant 22Ne/21Ne production for all samples during the first stage. These shielding levels, which are supported by estimates based on 36Cl production by neutron capture, indicate a possible relationship between depth of samples in the Mocs meteoroid and fall location in the strewn field.
Niobium and tantalum in carbonaceous chondrites: Constraints on the solar system and primitive mantle niobium/tantalum, zirconium/niobium, and niobium/uranium ratio
Authors: Jochum K. p. , Stolz A. j. , Mcorist G.
Published: February 2010

Abstract— We have determined Nb, Y, and Zr abundances in the carbonaceous chondrites Orgueil (CI), Murray (CM2), Murchison (CM2), Allende (CV3), and Karoonda (CK4), and in the eucrites, Pasamonte and Juvinas, by a recently developed spark source mass spectrometric technique using multiple ion counting (MIC‐SSMS). The abundance of Ta was determined in the same meteorites by radiochemical neutron activation analysis (RNAA). Precision of the MIC‐SSMS and RNAA techniques is ∼3% and ≤ 5%, respectively.

The new abundances for CI chondrites are: Nb = 0.247, Ta = 0.0142, Zr = 3.86, Y = 1.56 μg/g; or 0.699, 0.0202, 11.2, and 4.64 atoms/106 Si atoms, respectively. The values agree with earlier compilations, but they are a factor of 2 more precise than earlier analyses. Trace element concentrations in the CM, CV, and CK chondrites are higher than in the CI chondrite Orgueil by about 37, 86, and 120%, respectively, in agreement with the variable absolute contents of refractory lithophile elements in different groups of carbonaceous chondrites.

Of particular interest are the chondritic Nb/Ta, Zr/Nb, and Nb/U ratios, because these ratios are important tools for interpreting the chemical evolution of planetary bodies. We obtained Nb/Ta = 17.4 ± 0.5 for the carbonaceous chondrites and the Juvinas‐type eucrites investigated. Though this value is similar to previous estimates, it is much more precise. The same is true for Zr/Nb (15.5 ± 0.2) and Zr/Y (2.32 ± 0.12). In combination with recently published MIC‐SSMS U data for carbonaceous chondrites, we obtained a chondritic Nb/U ratio of 29 ± 2.

Because Nb, Ta, Zr, Y, and U are refractory lithophile elements and presumably partitioned into the silicate phase of the Earth during core formation, the elemental ratios may also be used to constrain evolution of the Earth's primitive mantle and, with the more precise determinations fractionation of Nb and Ta during magmatic processes and mantle‐crust interactions, can now be interpreted with greater confidence.
Formation of feldspathic and metallic melts by shock in enstatite chondrite Reckling Peak A80259
Authors: Fagan Timothy j. , Scott Edward r. d. , Keil Klaus , Cooney Thomas f. , Sharma Shiv k.
Published: February 2010

Abstract— The enstatite chondrite reckling peak (rkp) a80259 contains feldspathic glass, kamacite, troilite, and unusual sets of parallel fine‐grained enstatite prisms that formed by rapid cooling of shock melts. Metallic Fe,Ni and troilite occur as spherical inclusions in feldspathic glass, reflecting the immiscible Fe‐Ni‐S and feldspathic melts generated during the impact. The Fe‐Ni‐S and feldspathic liquids were injected into fractures in coarse‐grained enstatite and cooled rapidly, resulting in thin (≤ 10 μm) semicontinuous to discontinuous veins and inclusion trails in host enstatite. Whole‐rock melt veins characteristic of heavily shocked ordinary chondrites are conspicuously absent. Raman spectroscopy shows that the feldspathic material is a glass. Elevated MgO and SiO2 contents of the glass indicate that some enstatite and silica were incorporated in the feldspathic melt. Metallic Fe,Ni globules are enclosed by sulfide and exhibit Nienrichment along their margins characteristic of rapid crystallization from a Fe‐Ni‐S liquid. Metal enclosed by sulfide is higher in Si and P than metal in feldspathic glass and enstatite, possibly indicating lower O fugacities in metal/sulfide than in silicate domains. Fine‐grained, elongate enstatite prisms in troilite or feldspathic glass crystallized from local pyroxene melts that formed along precursor grain boundaries, but most of the enstatite in the target rock remained solid during the impact and occurs as deformed, coarsegrained crystals with lower CaO, Al2O3, and FeO than the fine‐grained enstatite. Reckling Peak A80259 represents an intermediate stage of shock melting between unmelted E chondrites and whole‐rock shock melts and melt breccias documented by previous workers. The shock petrogenesis of RKPA80259 reflects the extensive impact processing of the enstatite chondrite parent bodies relative to those of other chondrite types.
Shock magnetism in fine particle iron
Authors: DICKINSON Tamara L. , WASILEWSKI Peter
Published: February 2010

Abstract— All solid solar system bodies have been affected by impact to varying degrees, and, thus, magnetic records in these bodies may have been modified by shock events. Shock events may have overprinted all primordial magnetic records in meteorites. Shock metamorphism stages ranging from very little to extreme, when melting takes place, have been identified in meteorites. We are examining the creation and destruction of magnetic remanence associated with shock. In this paper, we develop a preliminary framework for understanding the magnetic properties of fine‐grained Fe particles (20–110 nm), which carry most of the remanent magnetization in lunar samples and, by extension, the kamacite phase in meteorite samples. Initial experiments on shock effects due to a first‐order shock‐induced crystallographic transformation are described. The first characterization of pre‐ and postshock magnetic properties for sized Fe particles and the first characterization of the transformation remanent magnetization (TMRM) associated with the face‐centered‐cubic (fcc) to body‐centered‐cubic (bcc) transformation in fine particle Fe spheres are described. This is equivalent to the 13 GPa transitions in bcc Fe. We show that the TMRM is in the same direction as the ambient magnetic field present during the shock, but is deflected from the field direction by 30–45° and that the remanence intensity is 1–2 orders of magnitude less than expected for thermoremanent magnetization (TRM) acquired during cooling through the Curie temperature. Isothermal remanence acquisition curves (RA) reveal the increasing magnetic hardness due to shock. Magnetic hysteresis loops are used to characterize the particle size and the shock‐induced magnetic anisotropy. Thermal demagnetization experiments describe the probable presence of particle size effects and the effects associated with recovery‐recrystallization due to the annealing that takes place during the thermomagnetic experiment. These observations have implications for paleofield determinations and the recognition of thermal unblocking. A TMRM mechanism could produce a shock overprint in a meteorite and might impart a significant directional feature in an asteroid magnetic signature.
The titanium contents of lunar mare basalts
Authors: GIGUERE Thomas A. , TAYLOR G. Jeffrey , HAWKE B. Ray , LUCEY Paul G.
Published: February 2010

Abstract—Lunar mare basalt sample data suggest that there is a bimodal distribution of TiO2concentrations. Using a refined technique for remote determination of TiO2, we find that the maria actually vary continuously from low to high values. The reason for the discrepancy is that the nine lunar sample return missions were not situated near intermediate basalt regions. Moreover, maria with 2–4 wt% TiO2are most abundant, and abundance decreases with increasing TiO2. Maria surfaces with TiO2>5 wt% constitute only 20% of the maria. Although impact mixing of basalts with differing Ti concentrations may smear out the distribution and decrease the abundance of high‐Ti basalts, the distribution of basalt Ti contents probably reflects both the relative abundances of ilmenite‐free and ilmenite‐bearing mantle sources. This distribution is consistent with models of the formation of mare source regions as cumulates from the lunar magma ocean.
Oral histories in meteoritics and planetary science: I. Edward Anders
Authors: MARVIN Ursula B.
Published: February 2010

Abstract— In this interview, taped in 2000 August, during the meeting of the Meteoritical Society in Chicago, Edward Anders ascribes his interest in meteorites to a single moment of inspiration while he was in graduate school. He then reviews those advances that he has found most exciting. Some were contributed by his own research group, but many by others. Among the topics are the following: origin of meteorites (lunar or asteroidal parent bodies, diamonds, Widmanstätten pattern, nebular condensation, meteorite orbits, asteroid spectra); primitive meteoritic matter (Cl chondrites, calcium‐aluminum‐rich inclusions (CAIs), solar‐system abundances, organic matter); meteorite ages (radiogenic ages, cosmic‐ray ages, charged particle tracks); classification of meteorites (chondrites, iron meteorites, unequilibrated chondrites); isotopic anomalies (oxygen, heavy elements, noble gases, interstellar grains); and meteorite impacts (impact craters, K/T mass extinction). Anders spent most of his career (1955–1991) at the University of Chicago where he was the Horace B. Horton Professor of Chemistry from 1973–1991. The Meteoritical Society honored Anders with its Leonard Medal in 1974, and he served as its president in 1991–1992. He then dropped out of science. After residing in Switzerland for several years, Anders returned to the USA where he maintains residences in Burlingame, California, and Chicago, Illinois. Today, Anders can be reached at: eanders1@concentric.net.
Beryllium‐boron and aluminum‐magnesium chronology of calcium‐aluminum‐rich inclusions in CV chondrites
Authors: Sugiura N. , Shuzou Y. , Ulyanov A.
Published: February 2010

Abstract— We have made Be‐B measurements in six calcium‐aluminum‐rich inclusions (CAIs) (mostly type B inclusions) from CV chondrites and compared them to Al‐Mg measurements. All CAIs show 10B excesses in melilite that are correlated with Be/B ratios. The initial 10Be/9Be ratio inferred from the correlation line is 6.2 times 10−4. In contrast to the Be‐B system in melilite, the Al‐Mg system in anorthite is disturbed. This is probably due to B diffusion in melilite being slow compared with Mg diffusion in anorthite. This suggests that Be‐B chronology may be useful for measuring time differences of high‐temperature (melting, condensation, etc.) events in the early solar system.
The age of the Ilumetsa meteorite craters in southeast Estonia
Authors: Raukas Anto , Tiirmaa Reet , Kaup Enn , Kimmel Kai
Published: February 2010

Abstract— The Ilumetsa impact craters were discovered in 1938 in the course of geological mapping. In the crater field area, the Middle Devonian bedrock consists of light‐yellow weakly cemented siltstones and sandstones of the Givetian Burtnieki Regional Stage, which are overlain by a 1–2 m thick layer of reddish‐brown loamy till. Põrguhaud, the biggest crater, has a diameter of 75–80 m at the top of the uplifted rim and is 12.5 m deep. The zone of authochtonous breccias below the apparent crater extends to 30 m deep. The crater is partly filled with a thin layer of gyttja and peat up to 2 m thick. Radiocarbon ages of 6030 ± 100 (TA‐310) and 5910 ± 100 (TA‐725) years B.P. from the lowermost organic layer and palynological evidence suggest that the age of the impact was ∼6000 14C years B.P. The Sügavhaud crater has a diameter of 50 m at the top of the rim and is 4.5 m deep. Organic matter on the bottom of the crater is absent. As precise age determination of the Ilumetsa craters by direct dating methods has proved inconclusive, we proposed a method of geological correlation which is based on the occurrence of impact spherules in lake and bog sediments around the crater field. Radiocarbon dating of samples from a peat layer with glassy spherules of impact origin in the Meenikunno Bog, 6 km southwest of the Ilumetsa crater field, yielded the ages of 6542 ± 50 (Tln‐2214) for the depth interval 5.6–5.7 m and 6697 ± 50 (Tln‐2316) years B.P. for the depth interval 5.7–5.8 m. These dates suggest that the Ilumetsa craters were formed ∼6600 years ago.