bluuebunny/crossref_metadata_2025 huggingface dataset:
Atmospheric behavior and extreme beginning heights of the thirteen brightest photographic Leonid meteors from the ground‐based expedition to China
Authors: Spurný Pavel , Betlem Hans , Leven Jaap van't , Jenniskens Peter
Published: February 2010

Abstract— Precise atmospheric trajectories including dynamic and photometric data on thirteen of the brightest Leonid fireballs have been determined from the double‐station photographic observations of Leonid meteors during the ground‐based expedition to China in 1998 November. the expedition was organized as a collaboration between the dutch and chinese academy of sciences and was supported by the leonid multi‐instrument aircraft campaign (mac) program (jenniskens and butow, 1999). All data presented here were taken at Xinglong Observatory and at a remote station, Lin Ting Kou near Beijing, on the night of 1998 November 16/17. At the Xinglong station, photographic cameras were accompanied by an all‐sky television camera equipped with an image intensifier and 15 mm fish‐eye objective in order to obtain precise timings for all observed meteors up to magnitude +2. Whereas beginning heights of photographed meteors are all lower than 130 km, those observed by the all‐sky television system are at ∼160 km, and for three brightest events, even > 180 km. Such high beginnings for meteors have never before been observed. We also obtained a precise dynamic single‐body solution for the Leonid meteor 98003, including the ablation coefficient, which is an important material and structural quantity (0.16 s2 km−2). From this and from known photometry, we derived a density of this meteoroid of 0.7 g/cm3. Also, all PE coefficients indicate that these Leonid meteors belonged to the fireball group IIIB, which is typical for the most fragile and weak interplanetary bodies. From a photometric study of the meteor lightcurves, we found two typical shapes of light curves for these Leonid meteors.
Simulation of the interaction of galactic cosmic‐ray protons with meteoroids: On the production of radionuclides in thick gabbro and iron targets irradiated isotropically with 1.6 GeV protons
Authors: Leya I. , Lange H‐J. , LÜPke M. , Neupert U. , Daunke R. , Fanenbruck O. , Michel R. , RÖSel R. , Meltzow B. , Schiekel T. , Sudbrock F. , Herpers U. , Filges D. , Bonani G. , Dittrich‐Hannen B. , Suter M. , Kubik P. w. , Synal H‐a.
Published: February 2010

Abstract— Thick spherical targets made of gabbro (R = 25 cm) and of steel (R = 10 cm) were irradiated isotropically with 1.6 GeV protons at the Saturne synchrotron at Laboratoire National Saturne (LNS)/CEN Saclay in order to simulate the interaction in space of galactic cosmic‐ray (GCR) protons with stony and iron meteoroids. Proton fluences of 1.32 × 1014 cm−2 and 2.45 × 1014 cm−2 were received by the gabbro and iron sphere, respectively, which corresponds to cosmic‐ray exposure ages of about 1.6 and 3.0 Ma. Both artificial meteoroids contained large numbers of high‐purity target foils of up to 28 elements at different depths. In these individual target foils, elementary production rates of radionuclides and rare gas isotopes were measured by x‐ and γ‐spectrometry, by low‐level counting, accelerator mass spectrometry (AMS), and by conventional rare gas mass spectrometry. Also samples of the gabbro itself were analyzed. Up to now, for each of the experiments, ∼500 target‐product combinations were investigated of which the results for radionuclides are presented here. The experimental production rates show a wide range of depth profiles reflecting the differences between low‐, medium‐, and high‐energy products. The influence of the stony and iron matrices on the production of secondary particles and on particle transport, in general, and consequently on the production rates is clearly exhibited by the phenomenology of the production rates as well as by a detailed theoretical analysis. Theoretical production rates were calculated in an a priori way by folding depth‐dependent spectra of primary and secondary protons and secondary neutrons calculated by Monte Carlo techniques with the excitation functions of the underlying nuclear reactions. Discrepancies of up to a factor of 2 between the experimental and a priori calculated depth profiles are attributed to the poor quality of the mostly theoretical neutron excitation functions. Improved neutron excitation functions were obtained by least‐squares deconvolution techniques from experimental thick‐target production rates of up to five thick‐target experiments in which isotropic irradiations were performed. A posteriori calculations using the adjusted neutron cross sections describe the measured depth profiles of all these simulation experiments within 9%. The thus validated model calculations provide a basis for reliable physical model calculations of the production rates of cosmogenic nuclides in stony and iron meteorites as well as in lunar samples and terrestrial materials.
Orthopyroxene as a geospeedometer: Thermal history of Kapoeta, Old Homestead 001, and Hughes 002 howardites
Authors: Domeneghetti M. c. , Molin G. m. , Triscari M. , Zema M.
Published: February 2010

Abstract— Single crystals of orthopyroxene from small fragments of the Kapoeta, Old Homestead 001, and Hughes 002 howardites were studied by x‐ray diffraction and microprobe analyses. The Fe‐Mg equilibrium distribution coefficients kD of the crystals were used to calculate the closure temperatures (Tc) using the calibration by Stimpfl et al. (1999). The compositions, the presence of exsolved augite lamellae, and the Tc values (from 365 to 385 °C) obtained for Kapoeta orthopyroxene s suggest that our fragment comes from a diogenitic cumulate clast. The more Fe‐rich composition, the absence of exsolved lamellae, and the higher Tc values (from 583 to 605 °C) measured in the Old Homestead 001 orthopyroxenes suggest that this fragment comes from a cumulitic clast affected by fast cooling at high temperature. For the Hughes 002 orthopyroxenes, close in composition to Old Homestead 001, the different Tc values (339, 358, and 607 °C) recorded by the various crystals and the presence of augite lamellae in the crystals with the lowest Tc support the hypothesis that this howardite sample is an unheated breccia containing a mixture of cumulitic orthopyroxenes with different thermal histories.
Hydrogen‐isotopic compositions in Allan Hills 84001 and the evolution of the martian atmosphere
Authors: Sugiura N. , Hoshino H.
Published: February 2010

Abstract— Hydrogen‐isotopic compositions of carbonate and maskelynite in Allan Hills (ALH) 84001 were measured by secondary ion mass spectrometry (SIMS). the δd values of both minerals show considerable deviation. The deviation seems to be caused by addition of varying amounts of terrestrial water in the case of carbonate. In the case of maskelynite, H is heterogeneously distributed and the deviation in δD values seems to be due to mixing of this indigenous heavy H with isotopically normal H present in the SIMS chamber. The indigenous δD value in ALH 84001 seems to be ∼2000%‰. Carbonate rather than maskelynite seems to be the main carrier of H in ALH 84001. Because ALH 84001 is ∼4 Ga old, the H‐isotopic composition suggests that a large fraction of the initial martian atmosphere had already escaped by 4 Ga.
The non‐trivial problem of meteorite pairing
Authors: Benoit Paul h. , Sears Derek w. g. , Akridge J. m. c. , Bland P. a. , Berry F. j. , Pillinger C. t.
Published: February 2010

Abstract— Pairing is the procedure of identifying fragments of a single meteorite fall (that were separated during atmospheric passage or during terrestrial history) by establishing the similarity of two or more meteorite fragments. We argue that pairing is governed by two principles, that only a single mismatch of properties is required to refute a proposed pairing, and that virtually all pairings bear some degree of uncertainty. Using data distributions for modern falls, we take a probability approach to estimate degrees of certainty associated with proposed pairings, emphasizing the importance of unusual features. For new pairing criteria or new analytical additions to old criteria, the degree of variation within individual meteorites must be delineated and the degree of variation within meteorite classes must be quantified. Criteria for pairing can be divided into (1) parent body history indicators, (2) meteoroid space history indicators, and (3) terrestrial history indicators. Included in these categories are 11 specific criteria, including petrographic textures, mineralogy and mineral composition, terrestrial age estimates, cosmic‐ray exposure ages, and natural thermoluminescence (TL) levels. Not all criteria are applicable to all meteorite types. About 2275 pairings suggested in the literature have been subjected to this analysis. Many literature pairings, especially those involving common meteorite types, bear large uncertainties due to lack of data.
Chlorine abundances in meteorites
Authors: Garrison Daniel , Hamlin Sarah , Bogard Donald
Published: February 2010

Abstract— We used the nuclear reaction 37Cl (n,γ) 38Ar, achieved during neutron irradiation for dating meteorites by the 39Ar‐40Ar technique, to calculate the elemental Cl concentration of 132 samples of 94 different meteorites (mostly finds) representing several different classes. determined k and ca concentrations are also reported. Total [Cl] varies considerably, both among meteorites of the same class and among different meteorite classes. The range in [Cl] is approximately 15–177 ppm for ordinary chondrites; approximately 24–650 ppm for enstatite chondrites; approximately 4–177 ppm for eucrites; approximately 7–128 ppm for mesosiderites; approximately 35–268 ppm for acapulcoites and lodranites; and approximately 12–507 ppm for winonaites and iron silicates. As expected, most differentiated meteorites have lower [Cl] compared to chondrites and iron silicates. Analyses of 11 interior samples (∼0.1 g each) of a large L6 chondrite varied over 68–129 ppm, which is a measure of the homogeneity of Cl distribution. By evaluating Ar release during stepwise sample degassing, we separated the Cl into low‐temperature and high‐temperature components, the former of which may consist of terrestrial contamination. Most samples show low‐temperature Cl concentrations of <40 ppm, but for several samples terrestrial Cl contamination constitutes significant fractions of the total Cl. Among most differentiated meteorites, finds show considerably greater low‐temperature [Cl] compared to falls.
Numerous unpaired meteorites exposed on a deflating playa lake at Lucerne Valley, California
Authors: Rubin Alan e. , Verish Robert s. , Moore Carleton b. , Oriti Ronald a.
Published: February 2010

Abstract— Out of 16 well‐characterized 1 to 37 g meteorite specimens recovered from Lucerne Dry Lake (an approximately 3 × 7 km playa in the southern Mojave Desert of California), there are 9 separate ordinary chondrite finds. The ratio of independent meteorites to total number of specimens (∼0.6) is among the highest in the world. This is due to lack of initial deep burial of the small meteorites, significant deflation of the lake exposing falls of individual stones (or small numbers of paired meteorites), and the absence of a large meteorite shower in the region. Playas appear to be excellent candidates for high‐yield meteorite‐collecting areas.
The meteorite collection of the Museo Nazionale dell'Antartide in Siena
Authors: Folco Luigi , Rastelli Nadia
Published: February 2010

Abstract— The catalogue for the meteorite collection of Siena's Museo Nazionale dell'Antartide is presented. The collection primarily contains meteorites recovered from the Antarctic by the Italian National Programme for Antarctic Research but also includes specimens from various locations around the world. To date (April 2000), the collection totals 722 specimens. Of these, 533 specimens are classified, including 500 chondrites, 21 achondrites, 3 stony‐iron meteorites, and 9 iron meteorites.
Refractory forsterite in primitive meteorites: Condensates from the solar nebula?
Authors: WEINBRUCH S. , PALME H. , SPETTEL B.
Published: February 2010

Abstract— All groups of chondritic meteorites contain discrete grains of forsteritic olivine with FeO contents below 1 wt% and high concentrations of refractory elements such as Ca, Al, and Ti. Ten such grains (52 to 754 μg) with minor amounts of adhering matrix were separated from the Allende meteorite. After bulk chemical analysis by instrumental neutron activation analysis (INAA), some samples were analyzed with an electron microprobe and some with an ion microprobe.

Matrix that accreted to the forsterite grains has a well‐defined unique composition, different from average Allende matrix in having higher Cr and lower Ni and Co contents, which implies limited mixing of Allende matrix.

All samples have approximately chondritic relative abundances of refractory elements Ca, Al, Sc, and rare‐earth elements (REE), although some of these elements, such as Al, do not quantitatively reside in forsterite; whereas others (e.g., Ca) are intrinsic to forsterite. The chondritic refractory element ratios in bulk samples, the generally high abundance level of refractory elements, and the presence of Ca‐Al‐Ti‐rich glass inclusions suggest a genetic relationship of refractory condensates with forsteritic olivine. The Ca‐Al‐Ti‐rich glasses may have acted as nuclei for forsterite condensation.

Arguments are presented that exclude an origin of refractory forsterite by crystallization from melts with compositions characteristic of Allende chondrules: (a) All forsterite grains have CaO contents between 0.5 and 0.7 wt% with no apparent zoning, requiring voluminous parental melts with 18 to 20 wt% CaO, far above the average CaO content of Allende chondrules. Similar arguments apply to Al contents. (b) The low FeO content of refractory forsterite of 0.2‐0.4 wt% imposes an upper limit of ∼1 wt% of FeO on the parental melt, too low for ordinary and carbonaceous chondrule melts, (c) The Mn contents of refractory forsterites are between 30 to 40 ppm. This is at least one order of magnitude below the Mn content of chondrule olivines in all classes of meteorites. The observed Mn contents of refractory forsterite are much too low for equilibrium between olivine and melts of chondrule composition, (d) As shown earlier, refractory forsterites have O‐isotopic compositions different from chondrules (Weinbruch et al., 1993a).

Refractory olivines in carbonaceous chondrites are found in matrix and in chondrules. The compositional similarity of both types was taken to indicate that all refractory forsterites formed inside chondrules (e.g., Jones, 1992). As refractory forsterite cannot have formed by crystallization from chondrule melts, we conclude that refractory forsterite from chondrules are relic grains that survived chondrule melting and probably formed in the same way as refractory forsterite enclosed in matrix. We favor an origin of refractory forsterite by condensation from an oxidized nebular gas.
Oral histories in meteoritics and planetary science: II. Robert N. Clayton
Authors: MARVIN Ursula B.
Published: February 2010

Abstract— In this interview, taped during the Meteoritical Society meeting in Chicago in 2000 August, Robert Clayton who started his career as a terrestrial geochemist, describes how he first analyzed meteorite samples with great reluctance after years of resisting every suggestion from his colleagues that he study them. He also relates how the unaccountable results he obtained while correcting oxygen‐18 analyses for carbon‐13 in CO2 made sense only when he finally realized that he actually was analyzing oxygen‐17. By sheer serendipity this result led to the fundamentally important new result that Allende and other meteorites carry an anomalous exotic component. Clayton now finds research on extra‐terrestrial materials to be extremely interesting and exciting, with new systems turning up every year. He regrets the lack of interest he encounters in many young scientists and hopes that the availability of martian samples will persuade more terrestrial geologists and geochemists to enter the field. Clayton made his career at the University of Chicago where he has served since 1980 as the Enrico Fermi Distinguished Service Professor. In 1982 The Meteoritical Society honored Robert Clayton with its Leonard Medal.
Oral histories in meteoritics and planetary science: III. Robert M. Walker
Authors: MARVIN Ursula B.
Published: February 2010

Abstract— In this interview, taped in 2000 August, during the meeting of the Meteoritical Society in Chicago, Robert Walker recalls that he began studying meteorites when he realized that they should display particle tracks caused by their bombardment by cosmic rays. Walker was much intrigued by the idea of finding fossil tracks from old cosmic rays. Among his more important accomplishments, he lists the discovery of tracks of extremely heavy cosmic rays in meteorites and those of very lowenergy solar flare particles in lunar samples. He has played a leadership role in research on interplanetary dust particles and on presolar grains in meteorites in an effort to learn more about the origins of the elements. Walker has spent most of his career at Washington University in St. Louis where he established the McDonnell Center for Space Science. In 1993, the Meteoritical Society presented him with the Leonard Medal.
From interstellar gas to the Earth‐Moon system
Authors: CAMERON A. G. W.
Published: February 2010

Abstract— This paper reports the current status of my smoothed particle hydrodynamic (SPH) simulations of the formation of the Moon. Since the Moon has recently been found to have been formed approximately 50 Ma after the solar nebula itself was formed, I have placed the lunar formation problem in the entire context of the formation and early evolution of the solar nebula. This set of processes remains controversial, and I have outlined what I believe to be the essential physical processes involved. These start with the formation of short‐lived (now extinct) radioactive nuclides in a massive supernova. Then follows the probable role of the supernova ejecta in triggering the collapse of a core in a molecular cloud to form the solar nebula, and the injection of the radioactivities into the collapsing cloud core. Most of the solar nebula dissipates to form the Sun, and what remains becomes relatively quiescent. Gas drag acting on interstellar grains and the dustballs formed from them, due both to vertical descent to midplane and inward spiralling in midplane, quickly causes growth of the solid materials to form planetesimals. When these bodies reach the kilometer size range and beyond, gravitational forces dominate the accumulation process. The accumulation of the Earth requires of the order of 108 years. About half‐way through that process the giant impact occurs with the next largest accumulating body near the protoearth. I have been simulating the giant impact using SPH with 100 000 particles. The simulations of three of these runs are depicted in detail with a series of color images. It is shown that conventional accumulation simulations that assume Keplerian orbits and that merge bodies upon collision are misleading because they cannot take account of tidal stripping nor of loss and gain of particles during the accumulation. In addition, the large rotational flattening of the protoearth renders the orbital motions nonkeplerian. The simulations that are shown in detail have been followed for just over a week of real time, and in that time the largest accumulating clump has reached about half or more of the mass of the Moon and additional clumps have accumulated into bodies in the range of 1 to 20% of a lunar mass. It is important to note that although these runs have given very promising results, the parameter space that could plausibly be associated with the giant impact is not yet adequately explored.
Petrogenesis of Allan Hills 84001: Constraints from impact‐melted feldspathic and silica glasses
Authors: GREENWOOD James P. , McSWEEN Harry Y.
Published: February 2010

Abstract— Compositional and textural relationships of shock‐melted glasses in the Allan Hills (ALH) 84001 meteorite have been examined by optical microscopy, electron microprobe analysis, and compositional mapping. The feldspathic and silica glasses exhibit features which constrain the relative timing of shock events and carbonate deposition in ALH 84001. The feldspathic glasses are stoichiometric and have compositions plausibly described as forming from igneous plagioclase (An27–39Ab58–68Or3–7) or sanidine (Or51Ab46An3), or from a mixture of these phases (mixed‐feldspar glasses). These observations argue against prior interpretations of feldspathic glasses as unflowed maskelynite, hydrothermal precipitates or alteration products, or shock melts that have undergone alkali volatilization. Carbonate was deposited around previously formed mixed‐feldspar glass clasts, suggesting that carbonate deposition occurred after the shock event that formed the granular bands (crushed zones) in this meteorite. SiO2‐rich glasses appear to be silica remobilized during shock, with little addition of other material.

A petrogenetic history of ALH 84001 consistent with the observations of feldspathic and silica glasses is (1) igneous crystallization and cumulate formation; (2) a pre‐carbonate shock event that formed the granular bands (crushed zones) and sheared chromites, and melted igneous plagioclase and sanidine to form mixed‐feldspar glasses; (3) carbonate and silica deposition in the granular bands (veining of plagioclase glasses by SiO2 and deposition of carbonate around mixed‐feldspar and plagioclase glass clasts); (4) a post‐carbonate shock event that resulted in invasion of carbonate by feldspathic melts, shock faulting and decarbonation of carbonate, high‐temperature mobilization of silica melts, and minor dissolution of orthopyroxene by silica melts.
The role of Fischer‐Tropsch catalysis in solar nebula chemistry
Authors: KRESS Monika E. , TIELENS Alexander G. G. M.
Published: February 2010

Abstract— Fischer‐Tropsch catalysis, the iron/nickel catalyzed conversion of CO and H2 to hydrocarbons, would have been the only thermally‐driven pathway available in the solar nebula to convert CO into other forms of carbon. A major issue in meteoritics is to determine the origin of meteoritic organics: are they mainly formed from CO in the solar nebula via a process such as Fischer‐Tropsch, or are they derived from interstellar organics? In order to determine the role that Fischer‐Tropsch catalysis may have played in the organic chemical evolution of the solar nebula, we have developed a kinetic model for this process. Our model results agree well with experimental data from several existing laboratory studies. In contrast, empirical rate equations, which have been derived from experimental rate data for a limited temperature (T) and pressure (P) range, are inconsistent with experimental rate data for higher T and lower P.

We have applied our model to pressure and temperature profiles for the solar nebula, during the epoch in which meteorite parent bodies condensed and agglomerated. We find that, under nebular conditions, the conversion rate of CO to CH4 does not simply increase with temperature as the empirically‐derived equations suggest. Instead, our model results show that this process would have been most efficient in a fairly narrow region that coincides with the present position of the asteroid belt. Our results support the hypothesis that Fischer‐Tropsch catalysis may have played a role in solar nebula chemistry by converting CO into less volatile materials that can be much more readily processed in the nebula and in parent bodies.
The Monahans chondrite and halite: Argon‐39/argon‐40 age, solar gases, cosmic‐ray exposure ages, and parent body regolith neutron flux and thickness
Authors: BOGARD Donald D. , GARRISON Daniel H. , MASARIK Jozef
Published: February 2010

Abstract— The Monahans H‐chondrite is a regolith breccia containing light and dark phases and the first reported presence of small grains of halite. We made detailed noble gas analyses of each of these phases. The 39Ar‐40Ar age of Monahans light is 4.533 ± 0.006 Ma. Monahans dark and halite samples show greater amounts of diffusive loss of 40Ar and the maximum ages are 4.50 and 4.33 Ga, respectively. Monahans dark phase contains significant concentrations of He, Ne and Ar implanted by the solar wind when this material was extant in a parent body regolith. Monahans light contains no solar gases. From the cosmogenic 3He, 21Ne, and 38Ar in Monahans light we calculate a probable cosmic‐ray, space exposure age of 6.0 ± 0.5 Ma. Monahans dark contains twice as much cosmogenic 21Ne and 38Ar as does the light and indicates early near‐surface exposure of 13–18 Ma in a H‐chondrite regolith. The existence of fragile halite grains in H‐chondrites suggests that this regolith irradiation occurred very early. Large concentrations of 36Ar in the halite were produced during regolith exposure by neutron capture on 35Cl, followed by decay to 36Ar. The thermal neutron fluence seen by the halite was (2–4) × 1014 n/cm2. The thermal neutron flux during regolith exposure was ∼0.4‐0.7 n/cm2/s. The Monahans neutron fluence is more than an order of magnitude less than that acquired during space exposure of several large meteorites and of lunar soils, but the neutron flux is lower by a factor of ≤5. Comparison of the 36Arn/21Necos ratio in Monahans halite and silicate with the theoretically calculated ratio as a function of shielding depth in an H‐chondrite regolith suggests that irradiation of Monahans dark occurred under low shielding in a regolith that may have been relatively shallow. Late addition of halite to the regolith can be ruled out. However, irradiation of halite and silicate for different times at different depths in an extensive regolith cannot be excluded.
Compositional properties of coexisting orthopyroxene and spinel in some Antarctic diogenites: Implications for thermal history
Authors: HERMANN H‐P. , GANGULY J.
Published: February 2010

Abstract— We analyzed the compositional profiles of coexisting orthopyroxenes and spinels in six diogenite samples from the Antarctic meteorite collection and used the data to constrain their thermal histories. The closure temperatures of Fe2+‐Mg exchange between spinel and orthopyroxene in these samples vary between ∼630 and 830 °C. However, those in other diogenite samples, for which the compositional data are available in the literature, extend up to ∼1125 °C. This wide range of closure temperatures suggests repeated excavation of the diogenites from their original sites over a long time interval during cooling. The orthopyroxene grains were found to be homogeneous in composition while two of the relatively large spinel grains in the samples Elephant Moraine (EET) 87530 and Thiel Mountains (TIL) 82410 showed compositional zoning near the rim. Modeling of the spinel zoning in TIL 82410 suggests that it developed during cooling under a regolith or ejecta blanket, possibly at a depth of ∼80–120 m, and that the spinel composition was homogeneous at ∼900 °C. A nonlinear cooling model in which the cooling rate is given by ηT(K)2, with η = 5.8 times 10−3 K−1Ma−1, leads to simulated retrograde zoning profile in spinel which match the observed profile in TIL 82410 very well.
A terrestrial origin for sulfate veins in CI1 chondrites
Authors: Gounelle Matthieu , Zolensky Michael E.
Published: February 2010

Abstract— White sulfate veins are a very well‐known petrological feature of the chemically primitive CI1 carbonaceous chondrites. Sulfate veins were first described in the Orgueil meteorite in 1961, almost one century after its fall. However, we have observed such veins to form easily during typical sample storage. We suggest that all CI1 sulfate veins formed during the terrestrial residence of these heavily brecciated, porous stones. Reacting with atmospheric water, sulfates originally present in the meteorites dissolved and remobilized, and/or sulfides oxidised, filling the many open spaces offered to them by the very porous rock. Sulfate veins in CI1 chondrites can no longer be used as evidence of a late‐stage oxidation event in the CI1 parent body, or of centimeter‐scale fluid transport on the parent asteroid.
Argon‐40‐argon‐39 chronology and petrogenesis along the eastern limb of the Moon from Luna 16, 20 and 24 samples
Authors: Cohen B. A. , Snyder G. A. , Hall C. M. , Taylor L. A. , Nazarov M. A.
Published: February 2010

Abstract— Eighteen new lithic fragments from the Soviet Luna missions have been analyzed with electron microprobe and 40Ar‐39Ar methods. Luna 16 basalt fragments have aluminous compositions consistent with previous analyses, but have two distinct sets of well‐constrained ages (3347 ± 24 Ma, 3421 ± 30 Ma). These data, combined with other Luna 16 basalt ages, imply that there were multiple volcanic events filling Mare Fecunditatis. The returned basalt fragments have relatively old cosmicray exposure (CRE) ages and may have been recovered from the ejecta blanket of a young (1 Ga), nearby crater. A suite of highlands rocks (troctolites and gabbros) is represented in the new Luna 20 fragments. One fragment is the most compositionally primitive (Mg# = 91–92) spinel troctolite yet found. Both troctolites have apparent crystallization ages of 4.19 Ga; other rocks in the suite have progressively younger ages and lower Mg#s. The age and composition progression suggests that these rocks may have crystallized from a single source magma, or from similar sources mobilized at the same time. Within the new Luna 24 basalt fragments is a quench‐textured olivine vitrophyre with the most primitive composition yet analyzed for a Luna 24 basalt, and several much more evolved olivine‐bearing basalts. Both new and previously studied Luna 24 very low‐Ti (VLT) basalt fragments have a unimodal age distribution (3273 ± 83 Ma), indicating that most returned samples come from a single extrusive episode within Mare Crisium much later than the Apollo 17 VLT basalts (3.6–3.7 Ga).
Noble gases in interplanetary dust particles, II: Excess helium‐3 in cluster particles and modeling constraints on interplanetary dust particle exposures to cosmic‐ray irradiation
Authors: Pepin R. O. , Palma R. L. , Schlutter D. J.
Published: February 2010

Abstract— Measurements of He isotopes in cluster interplanetary dust particles (IDPs) from stratospheric dust collector L2009 reveal anomalous 3He/4He ratios comparable to those seen earlier, up to ∼40x the solar wind ratio, in particles from the companion collector L2011. These overabundances of 3He in the L2009 samples are masked by much higher 4He contents compared to the L2011 particles, and are visible only in minor gas fractions evolved by stepwise heating at high temperatures.

Cosmic‐ray induced spallogenic reactions are efficient producers of 3He. The majority of this paper is devoted to a detailed assessment of the possible role of spallation in generating the 3He excesses in these and other cluster IDPs. A model of collisional erosion and fragmentation during inward transit through the interplanetary dust environment is used to estimate space lifetimes of particles from asteroidal and Edgeworth–Kuiper Belt sources. Results of the modeling indicate that Poynting–Robertson orbital evolution timescales of IDPs small enough to elude destruction on their way to Earth from either location are far shorter than the cosmic‐ray exposure ages required to account for observed 3He overabundances. Grains large enough to have sufficiently long space residence times are fragmented close to their sources.

An alternative to long in‐space exposure could be prolonged irradiation of particles buried in parent body regoliths prior to their ejection as IDPs. A qualitative calculation suggests, however, that collisional erosion of asteroidal upper‐regolith materials is likely to occur on timescales shorter than the > 1 Ga burial times needed for accumulation of spallogenic 3He to the levels seen in several cluster particles. In contrast, regoliths on Edgeworth–Kuiper Belt objects may be stable enough to account for the 3He excesses, and delivery of heavily pre‐irradiated IDPs to the inner solar system by short‐period Edgeworth–Kuiper Belt comets remains a possibility. A potential problem is that the expected associated abundances of spallation‐produced 21Ne appear to be absent, although here the present IDP data base is too sparse and for the most part too imprecise to rule out a spallogenic origin. Relatively short periods of pre‐ejection residence in asteroidal regoliths may be responsible for the curiously broad exposure age distributions reported for micrometeorites extracted from Greenland and sea‐floor sediments.
Space weathering on Eros: Constraints from albedo and spectral measurements of Psyche crater
Authors: Clark B. E. , Lucey P. , Helfenstein P. , Bell J. F. , Peterson C. , Veverka J. , Mcconnochie T. , Robinson M. S. , Bussey B. , Murchie S. L. , Izenberg N. I. , Chapman C. R.
Published: February 2010

Abstract— We present combined multi‐spectral imager (MSI) (0.95 μm) and near‐infrared spectrometer (NIS) (0.8–2.4 μm) observations of Psyche crater on S‐type asteroid 433 Eros obtained by the Near‐Earth Asteroid Rendezvous (NEAR)—Shoemaker spacecraft. At 5.3 km in diameter, Psyche is one of the largest craters on Eros which exhibit distinctive brightness patterns consistent with downslope motion of dark regolith material overlying a substrate of brighter material. At spatial scales of 620 m/ spectrum, Psyche crater wall materials exhibit albedo contrasts of 32–40% at 0.946 μm. Associated spectral variations occur at a much lower level of 4–8% (±2–4%). We report results of scattering model and lunar analogy investigations into several possible causes for these albedo and spectral trends: grain size differences, olivine, pyroxene, and troilite variations, and optical surface maturation. We find that the albedo contrasts in Psyche crater are not consistent with a cause due solely to variations in grain size, olivine, pyroxene or lunar‐like optical maturation. A grain size change sufficient to explain the observed albedo contrasts would result in strong color variations that are not observed. Olivine and pyroxene variations would produce strong band‐correlated variations that are not observed. A simple lunar‐like optical maturation effect would produce strong reddening that is not observed. The contrasts and associated spectral variation trends are most consistent with a combination of enhanced troilite (a dark spectrally neutral component simulating optical effects of shock) and lunar‐like optical maturation. These results suggest that space weathering processes may affect the spectral properties of Eros materials, causing surface exposures to differ optically from subsurface bedrock. However, there are significant spectral differences between Eros' proposed analog meteorites (ordinary chondrites and/or primitive achondrites), and Eros' freshest exposures of subsurface bright materials. After accounting for all differences in the measurement units of our reflectance comparisons, we have found that the bright materials on Eros have reflectance values at 0.946 μm consistent with meteorites, but spectral continua that are much redder than meteorites from 1.5 to 2.4 μm. Most importantly, we calculate that average Eros surface materials are 30–40% darker than meteorites.
Observations of 433 Eros from 1.25 to 3.35 microns
Authors: Rivkin A. S. , Clark B. E.
Published: February 2010

Abstract— We have spectrophotometrically observed 433 Eros, the target of the NEAR‐Shoemaker spacecraft, on 1995 December 4 from 1.25 to 3.35 μm. As expected, Eros shows no evidence of an absorption feature >5% in the 3 μm region, and is interpreted to have an anhydrous surface within observational uncertainties. Our observations in the JHK region agree with previous work by Chapman and Morrison (1976) and Murchie and Pieters (1996), but differ from the near‐infrared spectrometer spectra reported by Clark et al. (2001). Our calculations indicate that thermal flux from Eros is not responsible for this mismatch.
A petrologic and trace element study of Dar al Gani 476 and Dar al Gani 489: Twin meteorites with affinities to basaltic and lherzolitic shergottites
Authors: WADHWA M. , LENTZ R. C. F. , McSWEEN H. Y. , CROZAZ G.
Published: February 2010

Abstract— We present the results of a combined mineralogic‐petrologic and ion microprobe study of two martian meteorites recently recovered in the Lybian Sahara, Dar al Gani 476 (DaG 476) and Dar al Gani 489 (DaG 489). Having resided in a hot desert environment for an extended time, DaG 476 and DaG 489 were subjected to terrestrial weathering that significantly altered their chemical composition. In particular, analyses of some of the silicates show light rare earth element (LREE)‐enrichment resulting from terrestrial alteration. In situ measurement of trace element abundances in minerals allows us to identify areas unaffected by this contamination and, thereby, to infer the petrogenesis of these meteorites. No significant compositional differences between DaG 476 and DaG 489 were found, supporting the hypothesis that they belong to the same fall. These meteorites have characteristics in common with both basaltic and lherzolitic shergottites, possibly suggesting spatial and petrogenetic associations of these two types of lithologies on Mars. However, the compositions of Fe‐Ti oxides and the size of Eu anomalies in the earliest‐formed pyroxenes indicate that the two Saharan meteorites probably experienced more reducing crystallization conditions than other shergottites (with the exception of Queen Alexandra Range (QUE) 94201). As is the case for other shergottites, trace element microdistributions in minerals of the DaG martian meteorites indicate that closed‐system crystal fractionation from a LREE‐depleted parent magma dominated their crystallization history. Furthermore, rare earth element abundances in the orthopyroxene megacrysts are consistent with their origin as xenocrysts rather than phenocrysts.
Calcium‐aluminum‐rich inclusions in enstatite chondrites (II): Oxygen isotopes
Authors: FAGAN Timothy J. , McKEEGAN Kevin D. , KROT Alexander N. , KEIl Klaus
Published: February 2010

Abstract— In situ ion microprobe analyses of spinel in refractory calcium‐aluminium‐rich inclusions (CAIs) from type 3 EH chondrites yield 16O‐rich compositions (δ 18O and δ 17O about‐40‰). Spinel and feldspar in a CAI from an EL3 chondrite have significantly heavier isotopic compositions (δ 18O and δ 17O about −5‰). A regression through the data results in a line with slope 1.0 on a three‐isotope plot, similar to isotopic results from unaltered minerals in CAIs from carbonaceous chondrites. The existence of CAIs with 16O‐rich and 16O‐poor compositions in carbonaceous as well as enstatite chondrites indicates that CAIs formed in at least two temporally or spatially distinct oxygen reservoirs. General similarities in oxygen isotopic compositions of CAIs from enstatite, carbonaceous, and ordinary chondrites indicate a common nebular mechanism or locale for the production of most CAIs.
Modeling aqueous alteration of CM carbonaceous chondrites
Authors: ROSENBERG Nina D. , BROWNING Lauren , BOURCIER William L.
Published: February 2010

Abstract— Results from an inorganic geochemical modeling study support a scenario in which low‐temperature aqueous alteration of an anhydrous CM asteroidal parent body and melt water from H2O and CO2 ices produces the altered assemblage observed in CM carbonaceous chondrites (chrysotile, greenalite, tochilinite, cronstedtite and minor calcite and magnetite). We consider a range of possible precursor mineral assemblages, varying with respect to the Fe‐oxidation state of the initial anhydrous phases. The aqueous solutions produced by this alteration are generally strongly basic and reducing and a large quantity of H2, and possible CH4, gas can be released during aqueous alteration.
Ultraviolet irradiation of naphthalene in H2O ice: Implications for meteorites and biogenesis
Authors: BERNSTEIN Max P. , DWORKIN Jason P. , SANDFORD Scott A. , ALLAMANDOLA Louis J.
Published: February 2010

Abstract— The polycyclic aromatic hydrocarbon (PAH) naphthalene was exposed to ultraviolet radiation in H2O ice under astrophysical conditions, and the products were analyzed using infrared spectroscopy and high‐performance liquid chromatography. As we found in our earlier studies on the photoprocessing of coronene in H2O ice, aromatic alcohols and ketones (quinones) were formed. The regiochemistry of the reactions is described and leads to specific predictions of the relative abundances of various oxidized naphthalenes that should exist in meteorites if interstellar ice photochemistry influenced their aromatic inventory. Since oxidized PAHs are present in carbon‐rich meteorites and interplanetary dust particles (IDPs), and ubiquitous in and fundamental to biochemistry, the delivery of such extraterrestrial molecules to the early Earth may have played a role in the origin and evolution of life.
Petrology and geochemistry of Patuxent Range 91501, a clast‐poor impact melt from the L‐chondrite parent body and Lewis Cliff 88663, an L7 chondrite
Authors: MITTLEFEHLDT David W. , LINDSTROM Marilyn M.
Published: February 2010

Abstract— We have performed petrologic and geochemical studies of Patuxent Range (PAT) 91501 and Lewis Cliff (LEW) 88663. PAT 91501, originally classified as an L7 chondrite, is rather a unique, near total impact melt from the L‐chondrite parent body. Lewis Cliff 88663 was originally classified as an “achondrite (?)”, but we find that it is a very weakly shocked L7 chondrite.

PAT 91501 is an unshocked, homogeneous, igneous‐textured ultramafic rock composed of euhedral to subhedral olivine, low‐Ca pyroxene, augite and chrome‐rich spinels with interstitial albitic plagioclase and minor silica‐alumina‐alkali‐rich glass. Only ∼10% relic chondritic material is present. Olivine grains are homogeneous (Fa25.2–26.8). Low‐Ca pyroxene (Wo1.9–7.2En71.9–78.2Fs19.9–20.9) and augite (Wo29.8–39.0En49.2–55.3Fs11.8–14.9) display a strong linear TiO2‐Al2O3 correlation resulting from igneous fractionation. Plagioclase is variable in composition; Or3.0–7.7Ab79.8–84.1An8.2–17.2.‐Chrome‐rich spinels are variable in composition and zoned from Cr‐rich cores to Ti‐Al‐rich rims. Some have evolved compositions with up to 7.9 wt% TiO2. PAT 91501 bulk silicate has an L‐chondrite lithophile element composition except for depletions in Zn and Br. Siderophile and chalcophile elements are highly depleted due to sequestration in centimeter‐size metal‐troilite nodules.

The minerals in LEW 88663 are more uniform in composition than those in PAT 91501. Olivine grains have low CaO and Cr2O3 contents similar to those in L5–6 chondrites. Pyroxenes have high TiO2 contents with only a diffuse TiO2‐Al2O3 correlation. Low‐Ca pyroxenes are less calcic (Wo1.6–3.1En76.5–77.0Fs20.4–21.4), while augites (Wo39.5–45.6En46.8–51.1Fs7.6–9.4) and plagioclases (Or2.6–5.7Ab74.1–83.1An11.2–23.3) are more calcic. Spinels are homogeneous and compositionally similar to those in L6 chondrites. LEW 88663 has an L‐chondrite bulk composition for lithophile elements, and only slight depletions in siderophile and chalcophile elements that are plausibly due to weathering and/or sample heterogeneity.
Meteor storm evidence against the recent formation of lunar crater Giordano Bruno
Authors: WITHERS Paul
Published: February 2010

Abstract— It has been suggested that the formation of the 22 km diameter lunar crater Giordano Bruno was witnessed in June 1178 A.D. To date, this hypothesis has not been well tested. Such an impact on the Earth would be “civilization threatening”. Previous studies have shown that the formation of Giordano Bruno would lead to the arrival of 10 million tonnes of ejecta in the Earth's atmosphere in the following week. I calculate that this would cause a week‐long meteor storm potentially comparable to the peak of the 1966 Leonids storm. The lack of any known historical records of such a storm is evidence against the recent formation of Giordano Bruno. Other tests of the hypothesis are also discussed, with emphasis on the lack of corroborating evidence for a very recent formation of the crater.
Greenland superbolide event of 1997 December 9
Authors: PEDERSEN H. , SPALDING R. E. , TAGLIAFERRI E. , CEPLECHA Z. , RISBO T. , HAACK H.
Published: February 2010

Abstract— Data on the trajectory and orbit of an extremely bright bolide (superbolide) over Greenland on 1997 December 9 are given, and circumstances of the phenomenon and its observations are described. A surveillance video camera and satellite‐based records enabled computing the trajectory and orbit independently of visual sightings of casual observers. The superbolide body of about 36 000 kg penetrated the atmosphere with an initial velocity of 30.5 ± 1.7 km s−1. Its orbit was a long‐period orbit and seems to be at variance with the low value of ablation coefficient (0.017 kg MJ−1) derived from modeling the atmospheric trajectory. However, such an event has been documented previously. Also the intensity and brevity of the satellite‐detected light flares are highly unusual. The impact area of the main hypothetical remnant of the body is given. Search for meteorites was performed. No meteorites were recovered. Also analysis of snow samples gave no hint of meteoritic dust.
Low‐temperature phase decomposition in iron‐nickel metal of the Portales Valley meteorite
Authors: SEPP Birgit , BISCHOFF Addi , BOSBACH Dirk
Published: February 2010

Abstract—The Portales Valley meteorite provides an opportunity to investigate and compare the microstructure in Fe‐Ni metal of the metallic particles in the chondritic portion and in the metal veins. The low‐temperature phase decomposition of Fe‐Ni metal was investigated using scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The microstructure is formed as the Portales Valley meteorite cooled from high temperatures and includes the outer taenite rim, the cloudy zone, clear taenite, and martensite. Martensite in turn decomposes into a fine admixture of fcc rods in a bcc matrix. The width of the island phase of the cloudy zone in the metal particles of the chondritic portion and the metal veins can be used to estimate a low‐temperature cooling rate. The microstructural evidence indicates that the chondritic portions and the metal veins in the Portales Valley meteorite cooled together as a mixture with a cooling rate of roughly 6.5 K/Ma.
Authors' Reply
Authors: Rasmussen Kaare L. , Olsen Hans J. F. , Gwozdz Raymond , Kolesnikov Evgeniy M.
Published: February 2010

Abstract— Jull et al. propose an alternative interpretation of our depth vs. 14C data measured on a peat core from the central Tunguska impact site (Rasmussen et al., 1999). We find that the proposed alternative is untenable.
MUSES‐C target asteroid (25143) 1998 SF36: A reddened ordinary chondrite
Authors: BINZEL Richard P. , RIVKIN Andrew S. , BUS Schelte J. , SUNSHINE Jessica M. , BURBINE Thomas H.
Published: February 2010

Abstract— Near‐Earth asteroid (25143) 1998 SF36 is a planned target for the Japanese MUSES‐C sample return mission. High signal‐to‐noise and relatively high‐resolution (50 Å) visible and near‐infrared spectroscopic measurements obtained during this asteroid's favorable 2001 apparition reveal it to have a red‐sloped S(IV)‐type spectrum with strong 1 and 2 μm absorption bands analogous to those measured for ordinary chondrite meteorites. This red slope, which is the primary spectral difference between (25143) 1998 SF36 and ordinary chondrite meteorites, is well modeled by the spectrum of 0.05% nanophase iron (npFe0) proposed as a weathering mechanism by Pieters et al. (2000). Asteroid 1998 SF36 appears to have a surface composition corresponding to that of ordinary chondrite meteorites and is most similar in spectral characteristics and modeled olivine/pyroxene content to the LL chondrite class.