bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbonates in fractures of Martian meteorite Allan Hills 84001: Petrologic evidence for impact origin
Authors: SCOTT EDWARD R. D. , KROT ALEXANDER N. , YAMAGUCHI AKIRA
Published: February 2010

Abstract— Carbonates in Martian meteorite Allan Hills 84001 occur as grains on pyroxene grain boundaries, in crushed zones, and as disks, veins, and irregularly shaped grains in healed pyroxene fractures. Some carbonate disks have tapered Mg‐rich edges and are accompanied by smaller, thinner and relatively homogeneous, magnesite microdisks. Except for the microdisks, all types of carbonate grains show the same unique chemical zoning pattern on MgCO3‐FeCO3‐CaCO3 plots. This chemical characteristic and the close spatial association of diverse carbonate types show that all carbonates formed by a similar process. The heterogeneous distribution of carbonates in fractures, tapered shapes of some disks, and the localized occurrence of Mg‐rich microdisks appear to be incompatible with growth from an externally derived CO2‐rich fluid that changed in composition over time. These features suggest instead that the fractures were closed as carbonates grew from an internally derived fluid and that the microdisks formed from a residual Mg‐rich fluid that was squeezed along fractures.

Carbonate in pyroxene fractures is most abundant near grains of plagioclase glass that are located on pyroxene grain boundaries and commonly contain major or minor amounts of carbonate. We infer that carbonates in fractures formed from grain boundary carbonates associated with plagioclase that were melted by impact and dispersed into the surrounding fractured pyroxene. Carbonates in fractures, which include those studied by McKay et al. (1996), could not have formed at low temperatures and preserved mineralogical evidence for Martian organisms.
Oxygen isotopic record of silicate alteration in the Shergotty—Nakhla—Chassigny meteorite Lafayette
Authors: ROMANEK CHRISTOPHER S. , PERRY EUGENE C. , TREIMAN ALLAN H. , SOCKI RICHARD A. , JONES JOHN H. , GIBSON EVERETT K.
Published: February 2010

Abstract—Samples from a suite of Shergotty—Nakhla—Chassigny (SNC) meteorites were analyzed for their O isotopic ratios by a modified version of the laser fluorination technique. Measured isotopic ratios (17O/16O and18O/16O) from bulk samples of the Shergottites, EETA79001, Shergotty and Zagami; the Nakhlite Lafayette; and Chassigny are similar to those reported in the literature, as are those from olivine and pyroxene mineral separates from Lafayette.

Iddingsite, a preterrestrial alteration product of Lafayette, was measured for the first time as a separate phase. Oxygen isotopic ratios increase with the percentage of iddingsite in a sample to a maximum δ18O of 14.4% for a ∼90% separate. Based on these measurements, end‐member iddingsite has a δ18O of 15.6%, which places it among other18O‐enriched secondary phases (carbonate and silica) observed in SNC meteorites. The relatively large difference in δ18O between iddingsite and the olivine and pyroxene it replaces (∼11%) is typical of low‐temperature alteration products.

A range of crustal fluid δ18O values can be interpreted from the δ18O for end‐member iddingsite, assuming isotopic equilibrium was achieved during low‐temperature hydrous alteration (<100 °C; Treimanet al., 1993). The calculated range of values, −15 to 5%, depends on many factors including: (1) the modal mineralogy of iddingsite, (2) potential isotopic exchange among other O‐bearing phases such as host silicate and carbonate, and (3) exchange with evolved or exotic O reservoirs on Mars. Despite the lack of constraints, the calculated range is consistent with isotopic exchange, and possibly equilibria, among components of the CO2‐carbonate‐iddingsite‐H2O system at low temperature.

The SNC meteorite samples in this study have Δ17O values that are indistinguishable from bulk Mars (0.30%), except for a single, small sample of iddingsite that has an anomalous Δ17O of ∼1.4%. While analytical difficulties make isotopic measurements for this sample problematic, the Δ17O is similar in direction to Δ17O reported for waters extracted from bulk samples of Lafayette (Karlssonet al., 1992). If the Δ17O for iddingsite is confirmed, it can be concluded that evolved or exotic fluids on Mars have contributed volatiles to the O reservoir from which iddingsite formed 130 to 700 Ma ago.
The Kapoeta howardite: Implications for the regolith evolution of the howardite‐eucrite‐diogenite parent body
Authors: PUN AURORA , KEIL KLAUS , TAYLOR G. JEFF , WIELER RAINER
Published: February 2010

Abstract— A large hand sample and numerous polished thin sections, made from the hand sample, of the Kapoeta howardite and its many diverse lithic clasts were studied in detail by optical microscopy and electron microprobe techniques in an attempt to understand the surface processes that operated on the howardite‐eucrite‐diogenite (HED) parent body (most likely the asteroid 4 Vesta). Four unique, unusually large clasts, designated A (mafic breccia), B (granoblastic eucrite), D (howardite) and H (melt‐coated breccia), were selected for detailed study (modal analysis, mineral microprobe analysis, and noble gas measurements). Petrographic studies reveal that Kapoeta consists of a fine‐grained matrix made mostly of minute pyroxene and plagioclase fragments, into which are embedded numerous different lithic and mineral clasts of highly variable sizes. The lithic clasts include pyroxene‐plagioclase (eucrite), orthopyroxenite (diogenite), howardite, impact‐melt, metal‐sulfide‐rich, and carbonaceous chondrite clasts. The howardite clasts include examples of lithic clasts that constitute breccias‐within‐breccias, suggesting that at least two regolith generations are represented in the Kapoeta sample we studied. The clast assemblage suggests that repeated shock lithification was an important process during regolith evolution. Noble gas analyses of clast samples fall into two populations: (a) solar‐gas‐rich clasts H (rim only) and D and (b) clasts A and B, which are essentially free of solar gases. The concentrations of solar noble gases in the two matrix samples differ by a factor of ∼40. It appears that clast D is a true regolith breccia within the Kapoeta howardite (breccia‐within‐breccia), while clast H is a regolith breccia that has been significantly impact reworked. Our data indicate that the Kapoeta howardite is an extraordinarily heterogeneous rock in modal mineral and lithic clast abundances, grain size distributions, solar‐wind noble gas concentrations and cosmic‐ray exposure ages. These results illustrate the repetitive nature of impact comminution and lithification in the regolith of the HED parent body.
A transmission electron microscope study of iron‐nickel carbides in the matrix of the Semarkona unequilibrated ordinary chondrite
Authors: KELLER LINDSAY P.
Published: February 2010

Abstract— The fine‐grained matrix of the Semarkona unequilibrated ordinary chondrite contains an assemblage of Fe carbides that are associated with oxides, sulfides, carbonates, and hydrated silicates. The carbides consist of fine‐scale epitactic intergrowths of cohenite (Fe3C) and Hägg carbide (Fe5C2) that formed as by‐products of gas‐solid reactions on the Semarkona parent body. The carbide intergrowths resulted from prograde reactions at moderate temperatures in the presence of a highly reducing carbon‐bearing gas. The carburization occurred prior to the aqueous alteration episode that produced the Fe‐rich phyllosilicates throughout the interchondrule matrix and the thin magnetite rims surrounding the carbide grains. The occurrence of the carbide intergrowths places an upper limit of <500 °C on the maximum postaccretional thermal processing that occurred on the Semarkona parent body.
The cooling history of the Lewis Cliff 86010 angrite as inferred from kirschsteinite lamellae in olivine
Authors: MCKAY G. A. , MIYAMOTO M. , MIKOUCHI T. , OGAWA T.
Published: February 2010

Abstract— Olivine in the angritic meteorite Lewis Cliff (LEW) 86010 contains abundant exsolution lamellae of kirschsteinite. Compositional gradients adjacent to the interface in both host and lamellae were formed by diffusion of chemical components into and out of the lamellae during cooling and growth. We have compared these gradients with compositional profiles calculated from diffusion and heat flow equations to estimate the cooling rate and burial depth of the sample. The resulting values for cooling rate and burial depth depend on which values are used for the diffusion rate of Ca in olivine, and how measured diffusivities are extrapolated to the lower temperatures at which the lamellae grew.

If the highest diffusion coefficients are used, the cooling rates obtained from seven different lamellae range from 30 to 52 °C/year, with an average of 42 °C/year, and burial depths (assuming an overburden with a thermal diffusivity typical of solid rock) range from 14 to 17 m, with an average of 15 m. If the lowest reasonable diffusion coefficients are used, the cooling rates range from 1.4 to 2.2 °C/year, with an average of 1.7 °C/year, and the depths range from 68 to 83 m, with an average of 75 m.

For the highest Ca diffusivities, details of the compositional profiles near the olivine/kirschsteinite interface suggest that continuous cooling was greatly accelerated at a temperature near 600–700 °C. The simplest physical explanation for such an acceleration is excavation of the sample from its original burial depth by an impact event. If Ca diffusivities are lower, a two‐stage cooling history is not required.
Relationship between positive cerium anomaly and adsorbed water in Antarctic lunar meteorites
Authors: KAGI HIROYUKI , TAKAHASHI KAZUYA
Published: February 2010

Abstract— Concentrations of adsorbed water in single mineral grains of Antarctic lunar meteorites were determined with micro infrared (IR) spectroscopy. A relationship was found between the mineral's ability to adsorb water and the extent of Ce anomaly in rare earth element (REE) patterns precisely determined by the isotope dilution method using a thermal ionization mass spectrometer. Asuka (A) 881757, a lunar meteorite from the mare basalt without Ce anomaly, showed no trace of IR absorption due to adsorbed water. On the contrary, Yamato (Y) 791197‐109, Y‐86032‐98, Y‐86032‐95, Y‐791197‐115 and Y‐82192‐55A from the lunar highland exhibiting positive Ce anomaly showed IR absorption due to adsorbed water in some of their minerals. The detected water would be of terrestrial origin, because it was not structurally bound and easy to exchange judging from the spectral band shape. The contrast in concentration of adsorbed water between the lunar highland and the mare basalt is derived from a difference in the density of microfractures in mineral grains. Average concentrations of adsorbed water in the lunar highland meteorites were 3.8 mg/cm3 for pyroxene and olivine, and 1.7 mg/cm3 for plagioclase. This contrast between minerals is noteworthy because it has been known that Ce anomaly of pyroxene and olivine is larger than that of plagioclase both for Antarctic lunar meteorites and some lunar rocks. Furthermore, more adsorbed water was detected for minerals in meteorites that exhibit larger Ce anomaly. The present observations demonstrate that the extent of Ce anomaly correlated with the concentration of adsorbed water, which suggests that active mineral surface resulting in adsorption of water could be a trace of interaction forming Ce anomaly. Terrestrial weathering on Antarctica and REE fractionation on the Moon are discussed for possible origins of the Ce anomaly.
The ubiquitous presence of silica‐rich glass inclusions in mafic minerals: Examples from Earth, Mars, Moon and the aubrite parent body
Authors: VARELA M. E. , KURAT G. , CLOCCHIATTI R. , SCHIANO P.
Published: February 2010

Abstract— Highly silicic glass inclusions are commonly present in mafic minerals of xenolithic terrestrial upper mantle rocks (Schiano and Clocchiatti, 1994). They are believed to be the products of volatile‐rich silicic melts for which several sources have been proposed (Francis, 1976; Frey and Green, 1974; Schiano et al, 1995), but their origin(s) and, consequently, that of the glasses, remains unknown. However, in situ formation by very low‐degree partial melting seems to be possible as has been shown by experiments (e.g., Baker et al, 1995; Draper and Green, 1997).

Glass inclusions of silicic chemical composition are also present in some mafic minerals of achondritic meteorites (e.g., Fuchs, 1974; Okada et al, 1988; Johnson et al, 1991). The enstatite achondrites (aubrites) Aubres and Norton County, which record early planetesimal and planet formation in the solar nebula, and the olivine achondrite (chassignite) Chassigny, a rock believed to originate from Mars, contain abundant glass inclusions in their main minerals enstatite and olivine, respectively. Glasses of glass‐bearing inclusions have a highly silicic and volatile‐rich chemical composition similar, but not identical, to that of glass inclusions in terrestrial upper mantle peridotite minerals. Furthermore, glass inclusions in olivines from the Moon (e.g., Roedder and Weiblen, 1977) are also silica‐rich.

Because different physicochemical conditions prevail in the source regions of these rocks, the process of melting is, perhaps, not generally applicable for the generation of silica‐rich glasses. Alternatively, the glasses could have been formed via precipitation from silicate‐loaded fluids (Schneider and Eggler, 1986) or vapors. Another possible mechanism, not previously identified, could be dehydrogenation of nominally nonhydrous mafic minerals by heating or depressurization that should be accompanied by expulsion of excess silica and incompatible elements. This process will mimic low‐temperature, very low‐degree partial melting. It could account also for the highly variable glass/bubble ratios observed in glass inclusions in aubrite enstatites. We suggest that such a process could have been operating in the solar nebula, the Moon and Mars, and could be operating still on Earth.
Impact into unconsolidated, water‐rich sediments at the Marquez Dome, Texas
Authors: BUCHANAN PAUL C. , KOEBERL CHRISTIAN , REID ARCH M.
Published: February 2010

Abstract— The Marquez Dome, Leon County, Texas represents a 13 km diameter Paleocene/Eocene impact structure formed in largely unconsolidated sediments in a near‐shore environment. The present study is an analysis of samples from cores taken from boreholes drilled separately on the edge of the central uplift and in the surrounding annular basin. The borehole drilled in the annular basin of the structure penetrated a sequence of interbedded sands, silts, and shales that is typical of the stratigraphy of the surrounding area. In contrast, the borehole drilled on the edge of the central uplift penetrated material that is relatively homogeneous in chemical composition and texture and may represent a mixture of sand, silt, clay, and minor carbonate derived from deeper levels in the preimpact stratigraphy. Veins containing pseudotachylitic breccias are not found and are not expected in this environment because low‐strength target materials are not conducive to frictional melting. Similarly, the low strength and unconsolidated nature of these target materials are not conducive to the formation of other types of typical impact breccias (e.g., melt rocks or suevites). The absence of such lithologies results either from explosive ejection of these materials caused by the water‐rich character of the target sediments or, more probably, from removal of these materials by deeper postimpact erosion than has been suggested previously. Planar deformation features (PDFs) were not found in quartz grains from any of these samples. The scarcity of quartz grains with PDFs, which have only been reported in rare impact breccias from the central uplift, and the large amount of vertical displacement indicated for the central uplift of this structure may also be a consequence of the low strength of target materials.
Experimental studies of magnetite formation in the solar nebula
Authors: HONG Y. , FEGLEY B.
Published: February 2010

Abstract— Oxidation of Fe metal and Gibeon meteorite metal to magnetite via the net reaction 3 Fe (metal) + 4 H2O (gas) = Fe3O4 (magnetite) + 4 H2 (gas) was experimentally studied at ambient atmospheric pressure at 91–442 °C in H2 and H2‐He gas mixtures with H2/H2O molar ratios of ∼4–41. The magnetite produced was identified by x‐ray diffraction. Electron microprobe analyses showed 3.3 wt% NiO and 0.24 wt% CoO (presumably as NiFe2O4 and CoFe2O4) in magnetite formed from Gibeon metal. The NiO and CoO concentrations are higher than expected from equilibrium between metal and oxide under the experimental conditions. Elevated NiO contents in magnetite were also observed by metallurgists during initial stages of oxidation of Fe‐Ni alloys. The rate constants for magnetite formation were calculated from the weight gain data using a constant surface area model and the Jander, Ginstling‐Brounshtein, and Valensi‐Carter models for powder reactions. Magnetite formation followed parabolic (i.e., diffusion‐controlled) kinetics. The rate constants and apparent activation energies for Fe metal and Gibeon metal are:

These rate constants are significantly smaller than the parabolic rate constants for FeS growth on Fe metal in H2S‐H2 gas mixtures containing 1000 or 10 000 ppmv H2S (Lauretta et al., 1996a). The experimental data for Fe and Gibeon metal are used to model the reaction time of Fe alloy grains in the solar nebula as a function of grain size and temperature. The reaction times for 0.1–1 μm radius metal grains are generally within estimated lifetimes of the solar nebula (0.1–10 Ma). However, the calculated reaction times are probably lower limits, and further study of magnetite formation at larger H2/H2O ratios, at lower temperatures and pressures, and as a function of metal alloy composition is needed for further modeling of nebular magnetite formation.
Olivine in Martian meteorite Allan Hills 84001: Evidence for a high‐temperature origin and implications for signs of life
Authors: SHEARER C. K. , LESHIN L. A. , ADCOCK C. T.
Published: February 2010

Abstract— Olivine from Martian meteorite Allan Hills (ALH) 84001 occurs as clusters within orthopyroxene adjacent to fractures containing disrupted carbonate globules and feldspathic shock glass. The inclusions are irregular in shape and range in size from ∼40 μm to submicrometer. Some of the inclusions are elongate and boudinage‐like. The olivine grains are in sharp contact with the enclosing orthopyroxene and often contain small inclusions of chromite. The olivine exhibits a very limited range of composition from Fo65 to Fo66 (n = 25). The δ18O values of the olivine and orthopyroxene analyzed by ion microprobe range from +4.3 to +5.3‰ and are indistinguishable from each other within analytical uncertainty.

The mineral chemistries, O‐isotopic data, and textural relationships indicate that the olivine inclusions were produced at a temperature >800 °C. It is unlikely that the olivines formed during the same event that gave rise to the carbonates in ALH 84001, which have more elevated and variable δ18O values, and were probably formed from fluids that were not in isotopic equilibrium with the orthopyroxene or olivine. The reactions most likely instrumental in the formation of olivine could be either the dehydration of hydrous silicates that formed during carbonate precipitation or the reduction of orthopyroxene and spinel. If the olivine was formed by either reaction during a postcarbonate heating event, the implications are profound with regards to the interpretations of McKay et al. (1996). Due to the low diffusion rates in carbonates, this rapid, high‐temperature event would have resulted in the preservation of the fine‐scale carbonate zoning, while partially devolatilizing select carbonate compositions on a submicrometer scale (Brearley, 1998a). This may have resulted in the formation of the minute magnetite grains that McKay et al. (1996) attributed to biogenic activity.
Stratigraphic relations of australites in the Port Campbell Embayment, Victoria
Authors: SHOEMAKER Eugene M. , UHLHERR H. Ralph
Published: February 2010

Abstract— In the Port Campbell Embayment of Victoria, australites have been found in situ in channel deposits of the Hanson Plain Sand of Pliocene and Pleistocene age. The large majority of the australites, however, occur as a lag deposit at the basal contact of the Sturgess Sand of late Pleistocene and Holocene age and are spatially correlated with ferruginous sandstone clasts that are derived from the Hanson Plain Sand. Some of the tektites are imbedded in or bonded to the ferruginous sandstone clasts, but most are found as individual tektite fragments. A few percent of the tektites have nearly perfectly preserved, complete aerodynamically shaped forms. The sandstone clasts and associated tektites have been reworked from the much older underlying Hanson Plain and have been locally concentrated in the lag deposit. Some tektites also occur at higher levels in the Sturgess Sand, almost invariably in association with stone flakes, exotic stones transported by the aborigines and, locally, with middens of mollusc shells. Circumstantial evidence indicates that the aborigines transported the tektites found in the upper part of the Sturgess, particularly at Stanhope Bay. As Port Campbell australites unequivocally occur in strata much older than the late Pleistocene and Holocene Sturgess, there is no longer any conflict between the apparent stratigraphic age of the tektites and the middle Pleistocene ages obtained by various chronometric methods.
Chronology of dimict breccias and the age of South Ray crater at the Apollo 16 site
Authors: EUGSTER Otto
Published: February 2010

Abstract—We report the noble gas isotopic abundances of five dimict breccias and one cataclastic anorthosite that were collected at the Apollo 16 landing site. Orbital and surface photographs indicate that rays from South Ray crater, an almost 1 km wide young crater in the Cayley plains, extend several kilometers from their source into the area that was sampled by the Apollo 16 mission. Previous studies have shown that South Ray crater formed 2 Ma ago and that a large number of rocks might originate from this cratering event. On the basis of cosmic‐ray produced nuclei, we find that the six rocks investigated in this work yield the same lunar surface exposure age. Using literature data, we recalculate the exposure ages of additional 16 rocks with suspected South Ray crater origin and obtain an average exposure age of 2.01 ± 0.10 Ma. In particular, all nine dimict breccias (a type of rock essentially restricted to the Apollo 16 area consisting of anorthosite and breccia phases) dated until now yield an average ejection age of 2.06 ± 0.17 Ma. We conclude that they must originate from the Cayley formation or from bedrock underlying the Cayley plain. We determined the gas retention ages for the dimict breccias based on the40K‐40Ar and U,Th‐136Xe dating methods: rock 64425 yields a40K‐40Ar age of 3.96 Ga and rock 61016 a U,Th‐136Xe age of 3.97 Ga. These results, together with39Ar‐40Ar ages obtained by other workers for rocks 64535 (3.98 Ga) and 64536 (3.97 Ga), show that the dimict breccias formed 3.97 Ga ago.
Fireballs: Interpretation of airblast data
Authors: TATUM Jeremy B.
Published: February 2010

Abstract— When a meteoroid passes through the Earth's atmosphere, it may generate acoustic waves in the form of a conical shock front and again in an explosive terminal burst. These acoustic waves reach the ground and their arrival times may be recorded on seismograms. Equations are given (with numerical examples, and for various atmospheric models) to recover the track of the meteoroid, and possibly the meteorite, from times of arrival at the seismographic stations.
Space weathering on the Moon: Patina on Apollo 17 samples 75075 and 76015
Authors: WENTWORTH Susan J. , KELLER Lindsay P. , McKAY David S. , MORRIS Richard V.
Published: February 2010

Abstract— We studied patinas on lunar rocks 75075 and 76015 from the Apollo collection using a multi‐disciplinary approach, including scanning electron microscopy (SEM), energy dispersive x‐ray spectrometry (EDS), transmission electron microscopy (TEM), wavelength‐dispersive x‐ray (WDS) mapping, Mössbauer spectroscopy, spectral reflectance, and microspectrophotometry. Based on SEM petrography, we have defined three textural types of patina: glazed, fragmental, and classic (cratered). The presence of classic patina is diagnostic of lunar samples that have been exposed directly to the space weathering environment. It is characterized by the presence of microcraters and glass pancakes and is the patina type studied by earlier workers. Classic patina is found on 76015 but not on 75075. Glazed patina is found on both 76015 and 75075, whereas fragmental patina is found only on 75075. The glazed and fragmental patinas on 75075 were probably formed as a result of relatively large nearby impacts; and although these two types of patina are not strictly the result of direct exposure to the space weathering environment, they are important because they affect the optical properties of the rocks. Field emission gun SEM (FE‐SEM) of classic patina on 76015 shows evidence of possible solar wind sputtering erosion. Transmission electron microscope studies of 76015 reveal the presence of impact‐generated deposits and solar flare particle tracks which, like microcraters and pancakes, are diagnostic of direct exposure to space weathering processes. The outermost surface of the 76015 patina consists of an amorphous rim very much like the rims found on individual lunar soil grains; this amorphous patina rim probably formed by similar processes of impact‐generated vapor condensation and possible sputter deposition. Wavelength‐dispersive x‐ray element maps of polished thin sections of 75075 and 76015 indicate that patina compositions are poor indicators of the compositions and mineralogies of the rocks underlying them. On average, the reflectance spectra of patinas on both samples are slightly darker than those of their unweathered equivalents. Microreflectance measurements show that a thick patina can dramatically alter the optical properties of the rock on which it forms. The backscatter Mössbauer (BaMS) spectrum of a patina‐covered surface of 76015 is very similar to that of an unweathered surface, indicating that the Mössbauer signal is generated from beneath the patina. Because BaMS “sees” through surface space‐weathering effects to the underlying rock, this technique has great potential for use in robotic missions to other planetary bodies.
Surface analysis of stratospheric dust particles
Authors: ROST Detlef , STEPHAN Thomas , JESSBERGER Elmar K.
Published: February 2010

Abstract— A controversially discussed and yet central question in interplanetary dust particle (IDP) research is the degree of alteration of these particles during their residence in the stratosphere. Especially, the typical enrichment of Br in chondritic IDPs (on the average ∼21 × CI) has been inferred to be a result of contamination processes, probably invoking aerosol droplets. With time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS), we examined the surfaces of 13 stratospheric particles from the dust collector U2071. Six particles had severe, surface‐bound, silicone oil residues preventing a proper analysis of their surfaces. Six other particles—‐according to our scanning electron microscopy, energy dispersive x‐ray spectrometer (SEM‐EDS) studies preclassified as one (Fe,Ni)S‐rich IDP, one Ca‐rich particle, and four aluminum‐oxide spheres—‐carry the halogens F, Cl, and Br on the surface. At least for the aluminum‐oxide spheres, we provide unequivocal evidence for a surface correlation of halogens. This evidence, taken together with that from previous studies, proves a general stratospheric contamination process which has to be considered in IDP research.
The oxygen‐isotopic composition of Earth and Mars
Authors: FRANCHI I. A. , WRIGHT I. P. , SEXTON A. S. , PILLINGER C. T.
Published: February 2010

Abstract— The small difference between the O‐isotopic mass fractionation lines of the Earth and Mars has been measured precisely using a laser fluorination system. The precision achieved from the two sample sets is better than ±0.014‰, with the offset (Δ17O) between Mars and Earth measured as +0.321‰. This result shows that all the Shergotty—Nakhla—Chassigny (SNC) meteorites define a high level of isotopic homogeneity, comparable to that of crustal material on the Earth, indicating that these meteorites originate, unequivocally, from a single, common parent body (Mars). Allan Hills 84001, with its ancient age (4.56 Ga), shows that any initial heterogeneity imparted into Mars from the nebula was homogenised very early in the formation history of the planet.
Chemical studies of H chondrites‐10: Contents of thermally labile trace elements are unaffected by late heating
Authors: Wang Ming‐Sheng , Wolf Stephen F. , Lipschutz Michael E.
Published: February 2010

Abstract— We have used radiochemical neutron activation analysis (RNAA) to determine 15 trace elements, including 10 moderately to highly volatile ones—Rb, Ag, Se, Cs, Te, Zn, Cd, Bi, Tl, In (in increasing volatility order), in 6 H chondrite falls with low‐3He contents. These (plus prior RNAA data) provide a compositional database of 92 H4‐6 chondrite falls. Three suites of samples can be identified from their noble gas contents: 44 with “normal” contents and, therefore, “normal” orbits and cosmic‐ray exposure histories; 8 that lost radiogenic gases, presumably by shock late in their histories; and 17 that lost cosmogenic gases by heating during close solar approach. We used the standard multivariate statistical techniques of linear discriminant analysis and logistic regression to compare contents of the 10 moderately and highly volatile trace elements, listed above, in these three suites. We found no significant differences. This contrasts sharply with similar comparisons involving random falls and H4‐6 chondrites that landed on Earth at specific time intervals. Apparently, contents of volatile trace elements in H4‐6 chondrites were established early in their histories, and they are so retentively sited that loss during later heating episodes did not occur.
The nature of the Tunguska meteorite
Authors: BRONSHTEN V. A.
Published: February 2010

Abstract— Arguments in favor of the cometary origin of the Tunguska meteorite are adduced along with reasons against the asteroidal hypothesis. A critical analysis is given for the hypotheses by Sekanina (1983) and Chyba et al. (1993). On the basis of the azimuth and inclination of the trajectory of the Tunguska body with plausible values of the geocentric velocity, the semimajor axis of the orbit and its inclination to the ecliptic plane are calculated for this body. It is noted that the theory of the disintegration of large bodies in the atmosphere put forward by Chyba et al. (1993) is crude. Applying more accurate theories (Grigoryan, 1979; Hills and Goda, 1993) as well as taking into account the realistic shape of the body yield for the cometary body lower disruption heights than obtained by Chyba et al. Numerical simulations carried out by Svettsov et al. agree well with the cometary hypothesis and the analytical calculations based on Grigoryan's theory. The asteroidal hypothesis is shown not to be tenable: the complete lack of stony fragments in the region of the catastrophe, cosmochemical data (in particular, the results of an isotope analysis), and some other information contradict this hypothesis. It is shown that stony fragments that would have originated in the explosive disruption of the Tunguska body would not be vaporized by the radiation of the vapor cloud nor as a result of their fall to the Earth's surface.
Layered tektites of southeast Asia: Field studies in central Laos and Vietnam
Authors: Fiske Peter S. , Schnetzler Charles C. , Mchone John , Chanthavaichith Kong Kham , Homsombath Inpong , Phouthakayalat Thonkeo , Khenthavong Bounsou , Xuan Pham Tich
Published: February 2010

Abstract— We have recovered 18 kg of layered tektites from 10 tektite‐bearing localities in Laos and central Vietnam, including 5 localities around the town of Muong Nong (Laos). Several of these deposits originally contained several hundred kilograms of layered tektite fragments, and one fragmented mass may have been as large as 1000 kg. This is the largest single deposit of tektites yet reported.

In this region, layered tektite fragments are found in isolated clusters usually associated with a pebbly laterite horizon that is 0–1 m below the surface. Near Khe Sanh, Vietnam, we estimate the abundance of layered tektite fragments to be ∼100 g/m2. This is greater than five times the abundance estimated for northeast Thailand (Fiske et al., 1996).

In a region that extends from northeast Thailand, through central Laos, and into central Vietnam, we found only layered tektites, which confirmed the existence of a large (>50 000 km2) subfield of the Australasian strewn field with only layered tektites. The east‐west extent of the “layered‐only” subfield is well constrained, but little field data exist to constrain its north‐south extent.
Sodic plagioclase thermometry of type 6 ordinary chondrites: Implications for the thermal histories of parent bodies
Authors: NAKAMUTA Y. , MOTOMURA Y.
Published: February 2010

Abstract—The structural states of sodic plagioclase crystals of ∼50 μm in size from three H6, two L6, and one LL6 chondritic meteorites have been determined by measuring the Δ131 parameter with a Gandolfi camera after analyzing chemical compositions. The temperature for each sodic plagioclase crystal has been determined by plotting the Δ131 parameter, corrected for the influence of K, on the relation diagram between the Δ131 parameter and the temperature of synthesis of sodic plagioclase by Smith (1972). The temperature obtained is assigned to the crystallization temperature of sodic plagioclase, and the maximum plagioclase temperature for each meteorite can be assumed to correspond to the maximum temperature attained by each meteorite during metamorphism. The maximum metamorphic temperatures estimated are 725–742 °C for the H6 chondrites, 808–820 °C for the L6 chondrites, and 800 °C for the LL6 chondrite. These temperatures are lower than those based on Ca contents of clinopyroxenes (Dodd, 1981; McSweenet al., 1988) but are consistent with those based on Ca contents of orthopyroxenes (McSween and Patchen, 1989; Langenhorstet al., 1995; Jones, 1997). The K content of sodic plagioclase correlates with the temperature obtained from the structural state. This positive correlation suggests that sodic plagioclase has formed in the course of equilibration processes of alkali elements in prograde metamorphism (i.e., during heating processes). The results of this study (i.e., the maximum metamorphic temperature of the H6 chondrites is lower than that of the L6 chondrites by ∼80 °C, and meteorites of the same chemical group show very similar maximum metamorphic temperatures) are in accordance with the predictions of calculations based on the26Al heat source and the onion‐shell structure model of the parent bodies.
A search for large meteoroids in the Perseid stream
Authors: BEECH Martin , NIKOLOVA Simona
Published: February 2010

Abstract— We report on two surveys conducted during the times of Perseid shower maximum in 1997 and 1998. The first survey entailed the video monitoring of the Moon's disk with the intent of recording the optical flashes that should result when large meteoroids strike the lunar surface. The second survey consisted of a combination video camera and very low frequency (VLF) radiowave receiver system capable of detecting electrophonic meteors during their ablation in the Earth's atmosphere. Using standard ablation theory, we find that for a Perseid meteoroid to be capable of generating electrophonic sounds, it must have an initial mass in excess of 495 kg. We also find, as a result of the surveys, an upper limit of 2 × 10−17 m−2 s−1 to the flux of electrophonic Perseid meteors entering the Earth's atmosphere. Although our study indicates that large, meter‐sized meteoroids must, at best, be sparsely distributed within the Perseid stream, we briefly discuss some tantalizing lines of evidence, found from within the astronomical literature, that hint at their true existence.
Johnson Space Center's Leonids optical observations
Authors: PAWLOWSKI James F.
Published: February 2010

Abstract— The 1998 Leonid meteor shower was videotaped by NASA Johnson Space Center (JSC) personnel, Jim Pawlowski and Jerry Winkler, at Houston, Texas, and Anna Scott at Cloudcroft, New Mexico. The videotapes were screened and the Leonid meteors in the videotapes were analyzed. The outcome of this effort was tables of counts per hour over the viewing period and a comparison to the Leonids meteors mass distribution model (Matney, 1998, unpubl. data) used for risk assessment calculations associated with space shuttle missions. The comparison exhibited a difference between the observed data and the model. Perhaps this difference can be resolved when observations from other parts of the Earth are assimilated with JSC observations.
Airborne intensified charge‐coupled device observations of the 1998 Leonid shower
Authors: MURRAY Ian S. , HAWKES Robert L. , JENNISKENS Peter
Published: February 2010

Abstract— We have used dual coaxial microchannel plate image‐intensified monochrome charge‐coupled device (CCD) detectors run at standard NTSC frame rates (30 frames per second, fps) to study the Leonid meteor shower on 1998 November 17 from an airborne platform at an altitude of ∼13 km. These observations were part of NASA's 1998 Leonid multi‐instrument aircraft campaign (MAC). The observing systems had fields of view (width) of 16.3° and 9.5°, and limiting stellar sensitivities of +8.3m and +8.9m. During 12 h of recording, 230 meteors were detected, of which 65 were Leonid meteors. Light curves are presented for 53 of these meteors. The magnitudes at peak brightness of the meteors investigated were generally in the range from +4.0m to +6.0m. The mass distribution indices for the two samples are 1.67 and 1.44, with the former being based on the wider field of view dataset. The light curves were skewed with the brightest point towards the beginning of the meteor trail. The F parameter for points one magnitude below maximum luminosity had a mean value of 0.47 for the wider field system and 0.37 for the more sensitive narrower field system. We provide leading and trailing edge light curve slopes for each meteor as another indication of light curve shape. There were few obvious flares on the light curves, indicating that in‐flight fragmentation into a large number of grains is not common. There is variability in light curve shape from meteor to meteor. The light curves are inconsistent with single, compact body meteor theory, and we interpret the data as indicative of a two‐component dustball model with metal or silicate grains bonded by a lower boiling point, possibly organic, substance. The variation in light curve shape may be indicative of differences in mass distribution of the constituent grains. We provide trail length vs. magnitude data. There is only a slight hint of a bend at +5m in the data, representing the difference between meteors that have broken into a cluster of grains prior to grain ablation, and those that continue to fragment during the grain ablation phase. Two specific meteors show interesting light curve features. One meteor is nebulous in appearance, with significant transverse width. The apparent light production region extends for 450 m from the center of the meteor path. Another meteor has several main fragments, and evidence of significant separated fragments. We offer several suggestions for improvements for the 1999 Leonid MAC light curve experiment.
Vertical distribution of dust particles in the Earth's atmosphere during the 1998 Leonids
Authors: MATESHVILI Nino , MATESHVILI Giuli , MATESHVILI Iuri , GHEONDJIAN Lev , AVSAJANISHVILI Olga
Published: February 2010

Abstract— Photometric observations of the twilight sky were carried out during Leonids 1998. The obtained vertical distributions of aerosol between 20 and 140 km demonstrate the processes of the intrusion of fine meteor dust and its subsequent intra‐atmospheric dynamics. The characteristic radii of two fractions of the meteor dust particles were estimated by their sedimentation velocities. They varied within rp = 0.006–0.06 μm and rp = 19–81 μm limits depending on an assumed particle density within ρp = 0.4–4.0 g cm−3. The assumption of ρp = 2.0 g cm−3 gave radii of the two fractions to be 0.01 and 30 μm, respectively.
Very precise orbits of 1998 Leonid meteors
Authors: BETLEM Hans , JENNISKENS Peter , LEVEN Jaap van ‘t , KUILE Casper ter , JOHANNINK Carl , ZHAO Haibin , LEI Chenming , LI Guanyou , ZHU Jin , EVANS Steve , SPURNÝ Pavel
Published: February 2010

Abstract— Seventy‐five orbits of Leonid meteors obtained during the 1998 outburst are presented. Thirty‐eight are precise enough to recognize significant dispersion in orbital elements. Results from the nights of 1998 November 16/17 and 17/18 differ, in agreement with the dominant presence of different dust components. The shower rate profile of 1998 November 16/17 was dominated by a broad component, rich in bright meteors. The radiant distribution is compact. The semimajor axis is confined to values close to that of the parent comet, whereas the distribution of inclination has a central condensation in a narrow range. On the other hand, 1998 November 17/18 was dominated by dust responsible for a more narrow secondary peak in the flux curve. The declination of the radiant and the inclination of the orbit are more widely dispersed. The argument of perihelion, inclination, and the perihelion distance are displaced. These data substantiate the hypothesis that trapping in orbital resonances is important for the dynamical evolution of the broad component.
Coordinated observations of two large Leonid meteor fireballs over northern New Mexico, and computer model comparisons
Authors: ZINN J. , WREN J. , WHITAKER R. , SZYMANSKI J. , Revelle D. O. , PRIEDHORSKY W. , HILLS J. , GISLER G. , FLETCHER S. , CASPERSON D. , BLOCH J. , BALSANO R. , ARMSTRONG W. T. , AKERLOF C. , KEHOE R. , McKAY T. , LEE B. , KELLEY M. C. , SPALDING R. E. , MARSHALL S.
Published: February 2010

Abstract— This paper describes the coordinated results of several sets of measurements of two Leonid meteor fireballs over northern New Mexico at 1:32 and 3:06 MST, respectively, on the night of 1998 November 17. The measurements included visible band photometry on both events, as well as filtered 5890 Å all‐sky images of the Na airglow. Also, for the 3:06 a.m. event, we obtained an infrasound measurement of the hydrodynamic yield. For the 1:32 a.m. event, we obtained a set of visible band charge‐coupled device (CCD) camera images of the meteor train for times extending to 30 min after the initial impact. The measurement results have been combined to derive an optical efficiency for the intense early‐time optical flash, and the total explosion yields and masses for both of the meteors.

We have also done a set of numerical radiation, hydrodynamic, and chemistry computations to investigate the nature and distribution of the long‐lasting airglow. We attribute the brightest visible airglow to atomic O 5577 Å line emission, with additional contributions from atomic Na emission and NO2 chemiluminescence. The near‐infrared atmospheric bands of molecular O2 should be very strong as well. All of the band emissions are expected to show a hollow limb‐brightened structure.
Are ureilites residues from partial melting of chondritic material? The answer from MAGPOX
Authors: GOODRICH Cyrena Anne
Published: February 2010

Abstract— Calculations performed using MAGPOX show that no bulk compositions having chondritic Ca/Al ratio and within the range of chondritic Si/Mg ratios can produce the olivine‐pigeonite ureilites (which constitute 65% of those for which modal abundances are known) as residues of single‐stage equilibrium partial melting. Calcium/aluminum ratios of 2–3.5 × CI are required. In addition, all the ureilites could not have formed from a single composition at various degrees of reduction, because they show no correlation between pigeonite/olivine ratio and mg ratio. Materials with various Al/Mg ratios, ranging from subchondritic to superchondritic, are required. If these materials are primitive (i.e., created by nebular processes rather than planetary igneous processes), they are unknown in the meteorite record. Excess accretion (relative to chondrites) of 5–10 mol% of a high‐temperature condensate component, which was itself almost completely depleted in corundum due to early fractionation, could create the necessary compositions. The plausibility that such processes occurred on a parent‐body sized scale is difficult to assess. In contrast, lodranites can be produced as residues of ∼3–30% equilibrium partial melting of an average ordinary chondritic composition at the appropriate level of reduction. Although many features of ureilites suggest that they are relatively primitive residues produced by low degrees of melting of chondritic materials, and thus resemble lodranites and other groups of primitive achondrites, their predominantly pigeonite + olivine mineralogy remains difficult to explain within this simple scenario.
Purely physical separation of a small fraction of the Allende meteorite that is highly enriched in noble gases
Authors: MATSUDA Jun‐ichi , AMARI Sachiko , NAGAO Keisuke
Published: February 2010

Abstract— Fine material that floats during freeze‐thaw disaggregation of the Allende meteorite is greatly enriched in noble gases compared to the bulk meteorite. Not only the elemental concentrations, but also most isotopic ratios of the noble gases in this fraction, strongly suggest that this material is very similar to the gas‐rich carbonaceous residue isolated from the bulk meteorite by chemical treatment. The only significant difference in noble gas signature between our separated fraction and the chemical residues is that the 129Xe/132Xe ratio in the former is significantly lower than that in the latter, which suggests readsorption of 129Xe released from the dissolved minerals during the chemical treatment. This is the first time that a gas‐rich residue of a meteorite has been separated by a purely physical method alone. We also show that noble gases in phase Q and presolar diamond may be separable physically, although both are closely associated.
Australasian minitektites discovered in the Indian Ocean
Authors: PRASAD M. SHYAM , SUDHAKAR M.
Published: February 2010

Abstract— Large area sampling with a box core in the Indian Ocean has led to the discovery of minitektites (>1–3.75 mm long) and a tektite fragment (∼1.25 mm) occurring with microtektites belonging to the Australasian tektite strewn field. Minitektites and the microtektites are found to have similar major element compositions conforming to the Australasian tektite/microtektite chemistry. Earlier studies based on isotopic evidence, dating, and chemistry had provided evidence of a single large tektite strewn field; however, the physical association of tektites occurring with microtektites has been lacking. The present study provides such an association.