bluuebunny/crossref_metadata_2025 huggingface dataset:
The fusion crusts of stony meteorites: Implications for the atmospheric reprocessing of extraterrestrial materials
Authors: GENGE Matthew J. , GRADY Monica M.
Published: February 2010

Abstract— Fusion crusts develop on all meteorites during their passage through the atmosphere but have been little studied. We have characterized the textures and compositions of the fusion crusts of 73 stony meteorites to identify the nature of meteorite ablation spheres (MAS) and constrain the processes operating during the entry heating. Most chondrite fusion crusts are porphyritic and are dominated by olivine, glass, and accessory magnetite; whereas those of the achondrites are mainly glassy. Chondrite fusion crusts contain sulphide droplets with high‐Ni contents (>55 wt%). The partially melted substrate of ordinary chondrites (underlying the outer melted crusts) are dominated by silicate glass and composite metal, sulphide, and Cr‐bearing Fe‐oxide droplets that form as coexisting immiscible liquids. Enstatite chondrite substrates contain Cr‐ and Mn‐ bearing sulphides. The substrates of the carbonaceous chondrites comprise a sulphide‐enriched layer of matrix. The compositions of melted crusts are similar to those of the bulk meteorite. However, differences from whole rock suggest that three main processes control their chemical evolution: (1) the loss and reaction of immiscible Fe‐rich liquids, (2) mixing between substrate partial melts and bulk melts of the melted crust, and (3) the loss of volatile components by evaporation and degassing. Data from fusion crusts suggest that MAS produced at low altitude have compositions within the range of those of silicate‐dominated cosmic spherules that are formed by the melting dust particles. Meteorite ablation spheres produced at high altitude probably have compositions very different from bulk meteorite and will resemble cosmic spherules derived from coarse‐grained precursors.
Terrestrial microfossils in Antarctic ordinary chondrites
Authors: BURCKLE Lloyd H. , DELANEY Jeremy S.
Published: February 2010

Abstract— Microfossils have been separated and identified in four high metamorphic grade chondrites from Allan Hills and Queen Alexandra Range, Antarctica. Diatoms and opal phytoliths representing both marine and terrestrial flora were recognized among the dust removed from cracks in all meteorites studied. It is likely that contamination of Antarctic meteorites with such biogenic material is ubiquitous. Standard clean room procedures to avoid laboratory introduction of microfossils into the meteorites were followed, and the genera and species identified so far are characteristic of marine, freshwater, and continental environments. The most probable mechanism for introduction of the microfossils into the meteorites is eolian transport to and on the polar ice cap. It is likely that wind‐driven systems may sample atmospherically transported material from large portions of the southern hemisphere. Entrainment of terrestrial microfossils is probably a typical interaction of meteorites with the Antarctic environment and must be recognized and accounted for in any attempt to use Antarctic meteorites as sources of extraterrestrial life forms. Organic molecules derived from microfossils are likely to be pervasive throughout any crack network present in a meteorite at all scales from millimeter to submicron. Cracks are a ubiquitous consequence of weathering in and on the Antarctic ice and the probability that crack surfaces contain terrestrial organic materials is high.
The internal structures and densities of asteroids
Authors: WILSON Lionel , KEIL Klaus , LOVE Stanley J.
Published: February 2010

Abstract— Four asteroidal bodies (the Martian satellites Phobos and Deimos and the main‐belt asteroids 243 Ida and 253 Mathilde) have now been the subjects of sufficiently close encounters by spacecraft that the masses and sizes and, hence, the densities of these bodies can be estimated to ∼10%. All of these asteroids are significantly less dense than most members of the classes of meteorites identified as being compositionally most nearly similar to them on the basis of spectral characteristics. We show that two processes can act, independently or in concert, during the evolutionary histories of asteroids to produce a low bulk density. One of these processes is the result of one or more impact events and can affect any asteroid type, whereas the other can occur only for certain types of small asteroids that have undergone aqueous alteration.
Ascent and eruption of a lunar high‐titanium magma as inferred from the petrology of the 74001/2 drill core
Authors: WEITZ Catherine M. , RUTHERFORD Malcolm J. , III James W. HEAD , McKAY David S.
Published: February 2010

Abstract—An analysis of the orange glasses and crystallized beads from the 68 cm deep 74001/2 core has been conducted to understand the processes occurring during ascent and eruption of the Apollo 17 orange glass magma. Equilibrium between melt and metal blebs (Fe85Ni14Co1) within the core, along with Cr contents in olivine phenocrysts, suggest there was an oxidation of C and a reduction of the melt at an O fugacity of IW‐1.3 and 1320 °C to form CO gas at 200 bars or ∼4 km depth. This was followed by development of more oxidized conditions during ascent. Also during ascent, there was formation of euhedral, homogeneous Fo81olivine crystals and spinel crystals with higher Al and Mg contents than the smaller spinels in the crystallized beads. Both the metal blebs and Al‐rich spinels were trapped inside the Fo81olivine phenocrysts as they grew prior to eruption. The composition of the orange glasses are homogeneous throughout the core, except for a few distinct glasses at the top that appear to have been mixed in by micrometeorite reworking. A few glassy melt inclusions of orange glass composition trapped in the Fo81phenocrysts contain 600 ± 100 ppm S and ∼50 ppm Cl compared to the 200 ppm S and 50 ppm Cl in the orange glass melt when quenched. These inclusions therefore document the addition of 400 ppm S to the CO‐rich volcanic gas during the eruption.

The size and distribution of different volcanic beads in the Apollo 17 deposit indicate a mode of eruption in which the orange glasses and partially crystallized beads formed further away from the volcanic vent where cooling rates were faster. Progressively larger and more numerous crystals in the black beads reflect slower cooling rates at higher optical densities in the volcanic plume. The development of a brown texture in the orange glasses at the bottom of the core, where the black beads dominate, is interpreted to result from devitrification by subsolidus heating either as the orange glasses fell back through the hot plume or after deposition on the surface. The change from domination by orange glasses to black beads in the core probably reflects a decrease in gas content over time, which consequently would increase the plume optical density and favor slower cooling rates.
Ejection‐velocity distributions from impacts into coarse‐grained sand
Authors: CINTALA Mark J. , BERTHOUD Lucinda , HÖRZ Friedrich
Published: February 2010

Abstract— Velocities of ejecta from seven impacts of aluminum projectiles into coarse‐grained sand have been measured with a laser‐based apparatus that produces stroboscopic photographs of individual grains in ballistic flight. Speeds and angles of the majority of the ejecta can then be measured very precisely. There appears to be little effect of impact velocity on the functional relationship between the scaled, radial launch position and either the speed or angle of ejection; the seven experiments covered a range of impact velocities from 0.8 to 1.9 kms—1. The measured ejection speeds follow power‐law distributions, as predicted by dimensional analysis, but the angle of ejection is not constant throughout a given event as predicted. Indeed, the angle of ejection declines gradually with increasing radial distance from the impact point, but there are indications that the angle increases again as the position of the final crater's rim is approached. The exponents determined from scaled crater dimensions and ejection‐speed distributions are substantially different. Although this might imply that assumptions used in the dimensional analysis are not valid, it is also possible that the coarse sand, whose component grains were comparable in dimension to the diameter of the impactors, instead presented a target that was more of an inhomogeneous aggregate of large fragments than a uniform, continuous medium.
Petrology of the Asuka 881931 ureilite with special reference to crystallization of interstitial silicate melt
Authors: IKEDA Yukio
Published: February 2010

Abstract— The Asuka 881931 meteorite is an unbrecciated ferroan ureilite and consists mainly of equi—granular olivine and pigeonite grains, a metal—sulfide network, interstitial silicates, and glass. Peripheral portions of equigranular olivine grains are often replaced by fine‐grained forsterite—metal aggregates and sometimes by fine‐grained enstatite—metal aggregates. These aggregates may have been produced from the equigranular olivine by reduction. Peripheral portions of equigranular pigeonite grains also are sometimes replaced by fine‐grained orthopyroxene aggregates with tiny patches of Si‐rich glass and may have been produced from the pigeonite by reduction reaction with silicate melt. Interstitial silicates are mainly orthopyroxene, magnesian pigeonite, high‐Ca pyroxene (diopside/fassaite), and CaO‐poor enstatite; and they crystallized from interstitial silicate melt. Interstitial glass is classified into two types—‐Si‐poor and Si‐rich. The Si‐poor glass is always in contact with equigranular olivine, but the Si‐rich glass never contacts equigranular olivine and is in contact with pyroxene and the metal—sulfide network. Both types of glass were produced from an original interstitial silicate melt, but the Si‐poor glass formed mainly by fractional crystallization of pyroxenes, and the Si‐rich glass may have formed by addition of Si mainly from nearby metal—sulfide melt, as well as crystallization of pyroxenes. The Si‐poor and Si‐rich melts were finally quenched as interstitial glasses under rapid cooling conditions.
Argon‐40/argon‐39 analyses of samples from the Gardnos impact structure, Norway
Authors: Grier Jennifer A. , Swindle Timothy D. , Kring David A. , Melosh H. Jay
Published: February 2010

Abstract— We have conducted 40Ar/39Ar age dating on a sample of impact melt from the Gardnos impact structure in Norway in an attempt to better constrain the formation age of the crater. Current estimates of the age of the Gardnos crater cover a wide range and are as old as 900 Ma (Dons and Naterstad, 1992; French et al., 1997). The age spectra that we obtained from three samples are consistent with a thermal event at 385 ± 5 Ma (1σ). Because this differs greatly from the best stratigraphic age of ∼600 Ma, and because the minerals present in the dated sample are a metamorphic assemblage, we believe we have not dated the formation age of the crater. Instead we have probably dated the effect of the early Devonian collapse of the late Caledonian (Scandian) orogeny on these materials (Dons and Naterstad, 1992; French et al., 1997). Although it may be possible, it will be difficult to determine the age of the impact by isotopic means alone because of this widespread metamorphism. Detailed stratigraphic analyses of the crater fill sediments may be the most promising method for constraining the crater age.
Classification of ten new Nullarbor Region meteorites
Authors: BENEDIX G. K. , KEIL K. , MURAKAMI J. Y.
Published: February 2010

Abstract— We classified ten new ordinary chondrites found in 1993 in the Nullarbor Region of Western Australia, seven of which were found in the Reid area (Reid 018–024) and three in the Hughes area (Hughes 027–029). Six of these are H and four are L chondrites, with petrologic types ranging from 4 to 6 and shock classifications from S2 to S4. All of the samples are small and, in most cases, heavily weathered, making pairing difficult.
Properties and mixing of soil components in Apollo 17 double‐drive tube 79001/2
Authors: RAO M. N. , WENTWORTH S. J. , BASU A. , GARRISON D. H. , McKAY D. S.
Published: February 2010

Abstract— Previous studies of Apollo 17 double‐drive tube 79001/2 showed that portions of this lunar regolith segment have some unusual properties, such as very high Is/FeO values (Monis et al., 1989) and N contents (Stone and Clayton, 1989). To understand the geologic significance of these features in this core, we determined the grain‐size distribution and modal abundance of the petrographic constituents for samples from 12 different depths of the core. Also, we measured the elemental and isotopic compositions of noble gases in the coarse‐grained (150–250 μm) and fine‐grained (<20 μm) sample fractions from four depths of this core. The agglutinate abundance and 36Ar contents show depth‐related variations similar to those observed for Is/FeO and N in this core. Samples from the top (∼0.5 cm depth) and the bottom (∼45 cm depth) of the drive tube are related to Apollo 17 submature soils with about 250–300 Ma galactic cosmic‐ray (GCR) exposure age. But the soil at the top of the drive tube received additional surface irradiation for ∼2 Ma after deposition at Van Serg. The samples at intermediate depths (i.e., ∼7 cm (upper zone) and ∼20 cm (lower zone) of the 79001/2 core) show features characteristic of mixtures of Apollo 17 mature soils and finely comminuted regolith breccias having about 600–800 Ma GCR exposure age. The mixing ratios between the coarse and fine fractions of the intermediate‐depth samples are similar to each other. Though the mixing ratios for the samples from the top and the bottom of the core are also similar to each other, they differ significantly from the ratios at intermediate depths. The results presented here are consistent with the two‐component Van Serg core model proposed by Stone and Clayton (1989) and McKay et al. (1988).
A petrographical and geochemical study of quartzose nodules, country rocks, and dike rocks from the Upheaval Dome structure, Utah
Authors: KOEBERL Christian , PLESCIA J. B. , HAYWARD Chris L. , REMOLD Wolf Uwe
Published: February 2010

Abstract— Upheaval Dome, in Canyonlands National Park, Utah, USA, is a unique structure on the Colorado Plateau. It has earlier been interpreted as an impact structure or as a pinched‐off salt diapir. Some subrounded quartzose fragments were found in a ring depression near the eastern margin of the structure and, based on vesicularity and apparent flow structure, the fragments were interpreted by early researchers as “impactites.” Our petrographic studies show no indication of a high‐temperature history and are in agreement with a slow, low‐temperature formation of the quartz nodules. Composi***ionally, the lag deposit samples are almost pure SiO2. They show no chemical similarity to any of the possible target rocks (e.g., Navajo Sandstone), from which they should have formed by melting if they were impactites. Instead, the samples have relatively high contents of elements that indicate fluid interaction (e.g., hydrothermal growth), such as As, Sb, Ba, and U, and show positive Ce anomalies. Thus, we interpret the “lag deposit samples” as normal low‐temperature (hydrothermally‐grown?) quartz that show no indication of being impact‐derived. In addition, a petrographic and geochemical analysis of a series of dike samples yielded no evidence for shock metamorphism or a meteoritic component.
Simulating flash heating in a muffle tube furnace
Authors: MAHARAJ Susan V. , HEWINS Roger H.
Published: February 2010

Abstract— Very rapid heating is an important chondrule‐formation process, and it has not been clear whether conventional equipment, such as a muffle tube furnace, is adequate for the simulation of heating on a timescale of seconds. We present a method for measuring the internal temperature reached by a charge during rapid heating when the thermocouple response lags. We have constrained charge temperatures by monitoring the time required to melt metal wires of various compositions and melting points placed inside charges with furnace temperature at 1400, 1500, and 1600 °C. The times required for melting of the metal wires define the temperature paths inside the charges. At 1400 °C, a charge takes 31 s to reach 1399 °C; at 1500 °C, a charge takes 10 s to reach 1495 °C; and at 1600 °C, a charge takes 6 s to reach 1538 °C. Heating rates in vertical muffle tube furnaces are adequate for studying flash melting processes (i.e., of «1 min duration) invoked, for example, in the formation of chondrules.
Astronomical constraints on nebular temperatures: Implications for planetesimal formation
Authors: WOOLUM Dorothy S. , CASSEN Patrick
Published: February 2010

Abstract—Motivated by recent observations of T‐Tauri stars and the interpretation of these observations in terms of the properties of circumstellar disks, we derive internal (midplane) temperatures for disks around mature (age ∼1 Ma) T‐Tauri stars. The estimates are obtained by combining published results for disk masses, sizes, accretion rates, and surface temperatures. For 26 stars (for which adequate data are available), we derive midplane temperatures at 1 AU primarily in the range 200–800 K, and 100–400 K at 2.5 AU. It is likely that the solar nebula, at the same stage of evolution, contained planetesimals and objects destined to become meteorite parent bodies. Observations of young stellar objects at earlier stages of evolution (age ∼0.1 Ma) imply that accretion rates were, on the average, at least two orders of magnitude greater than the 10−8M⊙/year rates typical for mature T‐Tauri stars. Such high values would result in midplane temperatures at or near the silicate vaporization temperature in the terrestrial planet region.

If cooling of the solar nebula from such a hot epoch was responsible for establishing the pervasive elemental fractionation patterns found in chondritic meteorites, then objects in the asteroid belt must have grown rapidly (within 0.1 Ma) to sizes of ∼1 km, a conclusion consistent with current theories of planetesimal formation. However, the fact that primitive meteorite parent bodies escaped being melted by the decay of26Al then implies that further growth of at least some objects was essentially delayed for 2 Ma or more. Such a diminished growth rate appears to be consistent with simulations of the dynamics of solid bodies in the asteroid belt.

Other hypotheses seem less attractive. One might assume that the final cooling occurred only after the decay of26Al (i.e., more than a million years after calcium‐aluminum rich inclusion formation), or that26Al was not ubiquitous in the early solar system. But the first of these conjectures is incompatible with astronomical observations of T‐Tauri systems, and the second appears to be contradicted by the evidence for26Al in diverse meteoritic components. The remaining alternative would then appear to be that, despite a lack of supporting evidence, chondritic fractionation patterns reflect the net effect of many local heating and cooling events and have nothing to do with global nebular cooling. We conclude that the most plausible hypothesis is that both nebular cooling and coagulation of solids to kilometer‐sized objects occurred rapidly and that a substantial number of planetesimals in the asteroid belt remained smaller than a few kilometers in radius for at least 2 Ma.
Amino acid survival in large cometary impacts
Authors: PIERAZZO E. , CHYBA C. F.
Published: February 2010

Abstract— A significant fraction of the Earth's prebiotic volatile inventory may have been delivered by asteroidal and cometary impacts during the period of heavy bombardment. The realization that comets are particularly rich in organic material seemed to strengthen this suggestion. Previous modeling studies, however, indicated that most organics would be entirely destroyed in large comet and asteroid impacts. The availability of new kinetic parameters for the thermal degradation of amino acids in the solid phase made it possible to readdress this question.

We present the results of new high‐resolution hydrocode simulations of asteroid and comet impact coupled with recent experimental data for amino acid pyrolysis in the solid phase. Differences due to impact velocity as well as projectile material have been investigated. Effects of angle of impacts were also addressed. The results suggest that some amino acids would survive the shock heating of large (kilometer‐radius) cometary impacts. At the time of the origins of life on Earth, the steady‐state oceanic concentration of certain amino acids (like aspartic and glutamic acid) delivered by comets could have equaled or substantially exceeded concentrations due to Miller‐Urey synthesis in a CO2‐rich atmosphere. Furthermore, in the unlikely case of a grazing impact (impact angle ∼5° from the horizontal), an amount of some amino acids comparable to that due to the background steady‐state production or delivery would be delivered to the early Earth.
Formation of a martian pyroxenite: A comparative study of the nakhlite meteorites and Theo's Flow
Authors: LENTZ R. C. FRIEDMAN , TAYLOR G. J. , TREIMAN A. H.
Published: February 2010

Abstract— The unusual composition of the nakhlites, a group of pyroxenitic martian meteorites with young ages, presents an opportunity to learn about nonbasaltic magmatic activity on another planet. However, the limited number of these meteorites makes unraveling their history difficult. A promising terrestrial analog for the formation of the nakhlites is Theo's Flow in Ontario, Canada. This atypical, 120 m‐thick flow differentiated in place, forming distinct layered lithologies of peridotite, pyroxenite, and gabbro. Theo's pyroxenite and the nakhlites share strikingly similar petrographies, with concentrated euhedral to subhedral augite grains set in a plagioclase‐rich matrix. These two suites of rocks also share specific petrologic features, mineral and whole‐rock compositional features, and size and spatial distributions of cumulus grains. The numerous similarities suggest that the nakhlites formed by a similar mechanism in a surface lava flow or shallow intrusion. Their formation could have involved settling of crystals in a phenocryst‐laden flow or in situ nucleation and growth of pyroxenes in an ultramafic lava flow. The latter case is more likely and requires steady‐state nucleation and growth of clusters of pyroxene grains (and olivine in the nakhlites), circulating in a strongly convecting melt pool, followed by settling and continued growth in a thickening cumulate pile. Trapped pockets of intercumulus liquid in the pile gradually evolved, finally growing Fe‐enriched rims on cumulus grains. With sufficient evolution, the melt reached plagioclase supersaturation, causing rapid growth of plagioclase sprays and late‐stage mesostasis growth.
The 1998 Leonid multi‐instrument aircraft campaign—an early review
Authors: JENNISKENS Peter , BUTOW Steven J.
Published: February 2010

Abstract— The 1998 return of the Leonid shower was the target of the Leonid multi‐instrument aircraft campaign (Leonid MAC), an unusual two‐aircraft astronomical research mission executed near Okinawa, Japan. The prospect of a meteor storm brought 28 researchers of 7 nationalities together in a concerted effort to observe the shower by imaging, spectroscopic, and ranging techniques. This paper is a review of the major science issues that are behind the deployment of each of the present array of instruments and describes the interconnection of the various experiments. This was NASA's first astrobiology mission. The mission also aimed to study contemporary issues in planetary astronomy, in atmospheric sciences, and concerning the satellite impact hazard. First results of the participating observers are discussed and put in context, in preparation for the deployment of a planned second mission in November of 1999.
Activity of the 1998 Leonid shower from video records
Authors: JENNISKENS Peter
Published: February 2010

Abstract— Video observations of the Leonid shower aboard two aircraft in the 1998 Leonid multi‐instrument aircraft campaign and from ground locations in China are presented. Observing at altitude proved particularly effective, with four times higher rates due to low extinction and low angular velocity at the horizon. The rates, derived from a total of 2500 Leonid meteors, trace at least two distinct dust components. One dominated the night of 1998 November 16/17. This two‐day wide component was rich in bright meteors with r = N (m + 1)/N (m) ≈ 1.5 (s = 1.4) and peaked at an influx of 3.1 ± 0.4 × 10−12 m−2 s−1 (for particles of mass <7 × 10−5 g) at solar longitude Λ0 ≈ 234.52 (Eq. J2000). The other more narrow component peaked on 1998 November 17/18 at Λ0 = 235.31 ± 0.01. Rates were elevated above the broad component between Λ0 = 235.15 and 235.40, symmetric around the current node of the parent comet 55P/Tempel‐Tuttle, peaking at 5.1 ± 0.2 × 10−12 m−2 s−1. The population index was higher, r = 1.8 ± 0.1 (s = 1.7), but not as high as in past Leonid storms (r = 3.0). The flux profile of this component has an unusual asymmetric shape, which implies a blend of contributions from at least two different but relatively recent epochs of ejection. The variation of r across the profile might be due to mass‐dependent ejection velocities of the narrowest component. High rates of faint meteors occurred only in an isolated five‐minute interval at Λ0 = 235.198, which is likely the result of a single meteoroid breakup in space.
Infrasonic detection of a Leonid bolide: 1998 November 17
Authors: ReVELLE Douglas O. , WHITAKER Rodney W.
Published: February 2010

Abstract— During the early morning hours of the night of the peak of the annual Leonid meteor shower on 1998 November 17, a bright fireball (approximately −12 to −14 visual magnitude at 100 km in the zenith) was observed over northern New Mexico with visual sightings as far away from Los Alamos as Albuquerque (∼150 km to the south of Los Alamos), including direct persistent trail observations at the U. S. A. F. Starfire Optical Range (SOR), which is also near Albuqerque. This event did not produce any sonic boom reports, presumably because of its high altitude. It was also detected locally by an infrared radiometer at Sandia National Laboratory and by an intensified charge‐coupled device (CCD) camera located in Placitas, New Mexico. Subsequent investigations of the data from the six infrasound arrays used by Los Alamos National Laboratory (LANL) and operated for the Department of Energy as a part of the Comprehensive Test Ban Treaty (CTBT) Research and Development program for the International Monitoring System (IMS) showed the presence of an infrasonic signal from the proper direction at the correct time for this bolide from two of our six arrays (both located in Los Alamos). The infrasound recordings (i.e., the wave amplitude and period data) indicated that an explosion occurred in the atmosphere at a source height of ∼93.5 km (with respect to sea level) or ∼90 km with respect to the altitude of Los Alamos, having its origins slightly to the north and west of Los Alamos. Purely geometric solutions from the ground observers reports combined with direct measurements from the CCD camera at Placitas produced a source height of 91 ± 7 km. The signal characteristics analyzed from 0.5 to 3.0 Hz include a total duration of about 3–4 s for a source directed from Los Alamos toward 353.6 ± 0.4° measured from true north at a maximum elevation arrival angle of ∼72.7°. The latter was deduced on the basis of the observed signal trace velocities (for the part of the recording with the highest cross‐correlation) and ranged from a constant value of about 920–1150 m/s (depending on the window length used in the analysis) for a ray trajectory along a direct refractive path between the source and the Los Alamos arrays. The dominant signal frequency at maximum amplitude at Los Alamos was ∼0.71 Hz. These highly correlated signals had a peak to peak, maximum amplitude of ∼2.1 microbars (0.21 Pa). Using several methods that incorporate various observed signal characteristics, total distance traveled, etc., our analysis indicates that the bolide probably had a source energy of ∼1.14 t (TNT equivalent) or 4.77 × 109 J. This is ∼14.1× smaller than the source energy estimate made using the infrasonic, empirical source energy relationship for low‐altitude stationary point sources developed in the 1960s by the Air Force Technical Applications Center (AFTAC), Patrick Air Force Base, Florida. This relation was originally developed, however, for much larger source energies and at much longer ranges.
Mineralogy of the lunar crust: Results from Clementine
Authors: TOMPKINS Stefanie , PIETERS Carlé M.
Published: February 2010

Abstract— The central peaks of 109 impact craters across the Moon are examined with Clementine ultraviolet‐visible (UVVIS) camera multispectral data. The craters range in diameter from 40 to 180 km and are believed to have exhumed material from 5–30 km beneath the surface to form the peaks, including both upper and lower crustal rocks depending on whether craters have impacted into highlands or basins. Representative five‐color spectra from spectrally and spatially distinct areas within the peaks are classified using spectral parameters, including “key ratio” (which is related to mafic mineral abundance) and “spectral curvature” (linked to absorption band shape, which distinguishes between low‐ and high‐Ca pyroxene and olivine). The spectral parameters are correlated to mineralogical abundances, related in turn to highland plutonic rock compositions. The derived rock compositions for the various central peaks are presented in a global map. From these results, it is evident that the lunar crust is compositionally diverse, both globally and at local 100 m scales found within individual sets of central peaks. Although the central peaks compositions imply a crust that is generally consistent with previous models of crustal structure, they also indicate a more anorthositic crust than generally assumed, with a bulk plagioclase content of ∼81%, evolving from “pure” anorthosite near the surface towards more mafic, low‐Ca pyroxene‐rich compositions with depth (comparable to anorthositic norite). Evidence for mafic plutons occurs in both highlands and basins and represent all mafic highland rock types. However, the lower crust is more compositionally diverse than the highlands, with both a greater range of rock types and more diversity within individual sets of central peaks.
Temperature dependence of specific heat capacity and its effect on asteroid thermal models
Authors: GHOSH Amitabha , McSWEEN Harry Y.
Published: February 2010

Abstract— Asteroid thermal models have typically employed a constant value of specific heat capacity, although this parameter is a function of temperature. We examine whether incorporation of the temperature dependence of specific heat capacity is a necessary refinement and find that including it produces considerable differences in thermal history. Though the temperature effect is demonstrated in a representative calculation for a chondritic asteroid with 26Al decay as a heat source, this result also has implications for asteroidal thermal models based on electromagnetic induction heating or heating by impact, as well as for thermal models of the terrestrial planets.
Leonid outburst activity 1996: A broad structure and a first occurrence of a narrow peak of fainter meteors
Authors: LANGBROEK Marco
Published: February 2010

Abstract— In 1996, a broad outburst structure of bright Leonid meteors similar to the 1995 and the 1994 displays (Jenniskens, 1996; Langbroek, 1996b) was observed. In addition, a second narrow outburst structure of fainter meteors, which will be reported and discussed in this paper, has with certainty been observed. This observation marks the first detection of such a narrow structure in the new series of Leonid outbursts. It has a similar exponential activity behaviour and similar emphasis on fainter meteors as shown by the 1866 and 1966 Leonid storm structures. Similar narrow peaks have been observed in 1965 and 1969 (Jenniskens, 1995, 1996).

The broad 1996 structure of bright meteors peaked at November 17.31 ± 0.04 (λ 235°.28 ± 0.04 (2000.0)). The additional narrow structure peaked at November 17.20 ± 0.01 (λ 235°.172 ± 0.007). The occurrence of the narrow peak can best be explained as a first modest sign of presence of the meteoroid structure that should be responsible for the expected meteor storm activity of the Leonids in 1998–1999. The appearance 0.°085 before the node of 55P/Tempel‐Tuttle suggests that the expected 1998–1999 Leonid storms might peak just before passage through the node of the comet.
Distribution of lithium, beryllium, and boron in meteoritic chondrules
Authors: HANON Pascal , CHAUSSIDON Marc , ROBERT François
Published: February 2010

Abstract— The distribution of Li, Be, and B was studied by ion microprobe mass spectrometry in 36 chondrules from the Semarkona, Bishunpur, Allende, Clovis #1, and Hedjaz meteorites. Within a single chondrule, Li‐Be‐B concentrations can vary up to one order of magnitude. For example, in a chondrule from Hedjaz, concentrations range from 0.3 to 2.4 ppm for Li, from <0.001 to 0.17 ppm for Be, and from 0.4 to 5.5 ppm for B. Among chondrules from Semarkona and Bishunpur, clear crystal‐mesostasis partitioning was observed in nine chondrules for Li, in nine chondrules for Be, and in three chondrules for B. The heterogeneities in the distribution of Li, Be, and B in chondrules from Semarkona and Bishunpur appear to be primary features that were inherited from the chondrules' precursors and not totally obscured during the chondrules' formation. A redistribution of B was nevertheless observed at the whole‐rock scale for Allende (B‐Al2O3 correlation) and Hedjaz (B–SiO2 correlation).

At the scale of bulk chondrules, a robust correlation is observed for all studied meteorites between the B/Be and the B/Li ratios, which indicates that Li and Be are much less heterogeneously distributed in chondrites than B. Mean Li, Be, and B concentrations of chondrules ([Li] ≅ 0.83+0.86 ppm; [Be] ≅ 0.0430.027 ppm; [B] ≅ 0.89+3.71‐0.72 ppm) are consistent with those of Orgueil ([Li] ≅ 1.49 ppm; [Be] ≅ 0.0249 ppm; [B] ≅ 0.87 ppm), but the mean Li/Be ratio of chondrules (24.5+6.5‐9.1) is a factor of ∼4 depleted relative to Orgueil (Li/Be ratio of ∼78). Such a depletion is puzzling because no correlation between Li and Na or B has been found as would be expected to result from volatilization processes during chondrule melting and cooling. As a consequence, the exact abundance of solar system Li remains an open question.
Trajectory and orbit of the Tunguska meteorite revisited
Authors: Bronshten V. a.
Published: February 2010

Abstract— A critical survey is presented of all determinations of the azimuth and inclination of the Tunguska meteorite's trajectory based either on eyewitness testimonies or on the mathematical treatment of the forest‐leveling field in the area of the catastrophe. The eyewitness testimonies collected in the neighborhood of the Nizhnyaya Tunguska River indicate the most probable azimuth of the trajectory projection to be 104° from the north to the east, which is close to the most recent azimuth estimate from the forest‐leveling field, 99°. For the most part of the trajectory, its inclination could not exceed 15°. However, it is seen from aerodynamic calculations that the combined action of the gravity field and a nonzero aerodynamic lift could increase the inclination to 40° as the end of the trajectory was approached. Meteoroid orbits are calculated for a broad family of trajectories with azimuths ranging from 99° (Fast et al, 1976) to 137° (Krinov, 1949) and geocentric velocities ranging from 25 to 40 km/s. Orbits with large azimuth values (120° and larger) are shown to belong to the asteroidal type. They are succeeded by the orbits of short‐period and long‐period comets, whereas very small azimuth values and large geocentric velocities correspond to the region of hyperbolic orbits. Certain restrictions on the possible trajectory azimuths and geocentric velocities of the Tunguska body are imposed by this study.
The South Range Breccia Belt of the Sudbury Impact Structure: A possible terrace collapse feature
Authors: SCOTT Ronald G. , SPRAY John G.
Published: February 2010

Abstract— The South Range Breccia Belt (SRBB) is an arcuate, 45 km long zone of Sudbury Breccia in the South Range of the 1.85 Ga Sudbury Impact Structure. The belt varies in thickness between tens of meters to hundreds of meters and is composed of a polymict assemblage of Huronian Supergroup (2.49–2.20 Ga), Nipissing Diabase (2.2 Ga), and Proterozoic granitoid breccia fragments ranging in size from a few millimeters to tens of meters. The SRBB matrix is composed of a fine‐grained (∼100 μm) assemblage of biotite, quartz, and ilmenite, with trace amounts of plagioclase, zircon, titanite, epidote, pyrite, chalcopyrite, pyrrhotite, and occasionally chlorite. The SRBB hosts the Frood‐Stobie, Vermilion, and Kirkwood quartz diorite offset dykes, the former being associated with one of the largest Ni‐Cu‐PGE sulphide deposits in the world.

Optical petrography and whole‐rock geochemistry concur with previous studies that have suggested that the matrix of the SRBB is derived from comminution and at least partial frictional melting of the wall rock Huronian Supergroup lithologies. Rare earth element (REE) data from all sampled lithologies associated with the SRBB exhibit crustal signatures when normalized to C1 chondrite values. Additionally, REE data from the quartz diorites, disseminated sulphides in Sudbury Breccia, and a sample of an aphanitic biotite‐hornblende tonalite dyke exhibit flat slopes when compared to the mafic and felsic norites, quartz gabbro, and granophyre units of the Sudbury Igneous Complex (SIC), which suggests that these lithologies are representative of bulk SIC melt.

We suggest that the SRBB was formed by high strain‐rate (>1 m/s), gravity‐driven seismogenic slip of the inner ring of the Sudbury Impact Structure during postimpact crustal readjustment (crater modification stage). Failure of the hanging wall may have facilitated the injection of bulk SIC melt into the SRBB, along with the Ni‐Cu‐PGE sulphides of the Frood‐Stobie deposit. Postimpact Penokean (1.9–1.7 Ga) tectonism, particularly northwest‐directed shearing along the South Range Shear Zone and associated thrust faulting, could account for the present subvertical orientation of the SRBB, and the apparent lack of a connection at depth with the SIC.
Bo Xian (LL3.9): Oxygen‐isotopic and mineralogical characterisation of separated chondrules
Authors: LI Chunlai , BRIDGES John C. , HUTCHISON Robert , FRANCHI Ian A. , SEXTON Arabelle S. , OUYANG Ziyuan , PILLINGER Colin T.
Published: February 2010

Abstract— We report the results of a mineralogical and O‐isotopic study of 362 chondrules disaggregated from the Bo Xian chondrite. The range of mineral compositions (Fa = 0.8–31.2%, mean = 23.5%, mode = 27–28%) are consistent with a reclassification of this meteorite from LL4 to LL3.9. Chondrule diameters range from 0.20 to 3.40 mm (mean = 0.74 mm) in the disaggregated population. A lower mean diameter (0.64 mm) calculated from thin‐section measurements partly reflects the high proportion of chondrule fragments. The chondrule size distribution, which is approximately log‐normal, is consistent with size‐sorting mechanisms. This sorting could be linked to the fragmentation of many chondrules on the parent body. However, in detail, the variation in diameter of different chondrule types and a hiatus in the size distribution at 0.6 mm indicate that there may have been complex controls perhaps partly being determined by the chondrule formation mechanism. Seven percent of the sectioned chondrules (102) contain chemically fractionated mineral assemblages: cristobalite‐bearing and Al‐rich. This significant degree of chemical heterogeneity probably resulted from both igneous and volatility controls.

Oxygen‐isotopic compositions were determined on mineral separates and 16 of the sectioned chondrules. Three separate isotopic exchange events have been identified. The dominant one is a low‐temperature hydrous gas‐solid exchange event between 16O‐rich solid and 16O‐poor gas reservoirs that lay along a slope 1.0 line on three‐isotope plots. Partial equilibration with the gas by feldspar and cristobalite, which exchanged more rapidly than olivine or pyroxene, led to formation of a slope 0.77 mixing line for Bo Xian and other LL chondrites. Mineralogy is the dominant control on the extent of this exchange; no relationship between isotopic composition and chondrule texture or size was identified. The feldspar separate and cristobalite‐rich chondrules have the most 16O‐poor compositions. Subsequently, thermal metamorphism in the parent body led to partial isotopic equilibration between the different mineral phases. A third exchange event, predating the other two events, is probably shown by one of the Al‐rich chondrules. This has an 16O‐rich composition, lying below the terrestrial fractionation line. Another Al‐rich chondrule has a normal ordinary chondrite isotopic composition. It is not clear whether the isotopic fractionation recorded in some Al‐rich chondrules can be achieved by the dominant gas‐solid exchange. Instead, the precursor O to the mineral phases may have become 16O‐rich during an earlier phase of mass‐independent fractionation.
A multi‐step model for the origin of E3 (enstatite) chondrites
Authors: HUTSON Melinda , RUZICKA Alex
Published: February 2010

Abstract— It appears that the mineralogy and chemical properties of type 3 enstatite chondrites could have been established by fractionation processes (removal of a refractory component, and depletion of water) in the solar nebula, and by equilibration with nebular gas at low‐to‐intermediate temperatures (approximately 700–950 K). We describe a model for the origin of type 3 enstatite chondrites that for the first time can simultaneously account for the mineral abundances, bulk‐chemistry, and phase compositions of these chondrites by the operation of plausible processes in the solar nebula. This model, which assumes a representative nebular gas pressure of 10−5 bar, entails three steps: (1) initial removal of 56% of the equilibrium condensed phases in a system of solar composition at 1270 K; (2) an average loss of 80–85% water vapor in the remaining gas; and (3) two different closure temperatures for the condensed phases. The first step involves a “refractory element fractionation” and is needed to account for the overall major element composition of enstatite chondrites, assuming an initial system with a solar composition. The second step, water‐vapor depletion, is needed to stabilize Si‐bearing metal, oldhamite, and niningerite, which are characteristic minerals of the enstatite chondrites. Variations in closure temperatures are suggested by the way in which the bulk chemistry and mineral assemblages of predicted condensates change with temperature, and how these parameters correlate with the observations of enstatite chondrites. In general, most phases in type 3 enstatite chondrites appear to have ceased equilibrating with nebular gas at approximately 900–950 K, except for Fe‐metal, which continued to partially react with nebular gas to temperatures as low as ∼700 K.
Sequential deformation of plains at the margins of Alpha Regio, Venus: Implications for tessera formation
Authors: GILMORE Martha S. , HEAD James W.
Published: February 2010

Abstract— The boundaries between the highly deformed tessera terrain and adjacent volcanic plains are primarily those of embayment, where the tessera are stratigraphically older than the plains. Previous studies show that <3% of these boundaries display evidence of tectonic tilting after the emplacement of the plains. One of these unusual boundaries is the western margin of Alpha Regio tessera, a zone ∼ 100 km in width that separates the plains from the interior structures of Alpha. This zone is characterized by margin parallel, fine‐scale (1–5 km) fractures, graben, and ridges that truncate and postdate the broad‐scale (10–30 km) ridges and troughs of the interior of Alpha. The western margin is embayed by several volcanic plains units that are progressively tilted and deformed by graben with closer proximity to Alpha Regio. The earliest deformation of the plains consists of northeast‐trending graben ∼1 km in width that are similar in morphology and spacing to graben that deform intratessera plains and plains at the eastern boundary of Alpha. Northwest‐trending graben then formed over an interval marked by the emplacement of two additional plains units; their similarity to northwest‐trending structures emanating from Eve corona and the Lada Terra rift suggests a possible genetic relationship. The tilting of the plains adjacent to western Alpha implies relative vertical movement of the margin, either uplift of tessera or downwarping of plains subsequent to the formation and relaxation of the interior of Alpha Regio. Subsidence of plains at this locale is supported by the presence of a basin to the west of Alpha surrounded by a fracture belt contiguous with western Alpha. Thus, the fractures and deformation at the western boundary of Alpha may be related to the formation of a basin to the west of Alpha with some influence from the northernmost extension of the Lada Terra rift. Such a basin is not present at a section along the eastern boundary of Alpha Regio, where the origin of tilted plains remains equivocal. We conclude that the deformation along the western margin of Alpha Regio is not directly related to the process of tessera formation but is an example of tessera modification and is consistent with the stratigraphic position of tessera as the oldest unit observed on Venus.
Mineralogical characterization of primitive, type‐3 lithologies in Rumuruti chondrites
Authors: BISCHOFF A.
Published: February 2010

Abstract— Rumuruti (R) chondrites constitute a new, well‐established chondrite group different from the carbonaceous, ordinary, and enstatite chondrites. Many of these samples are gas‐rich regolith breccias showing the typical light‐dark structure and consist of abundant fragments of various parent‐body lithologies embedded in a fine‐grained olivine‐rich matrix. Unequilibrated type‐3 lithologies among these fragments have frequently been mentioned in various publications. In this study, detailed mineralogical data on seven primitive fragments from the R‐chondrites Dar al Gani 013 and Hughes 030 are presented. The fragments range from ∼300 μ in size up to several millimeters. Generally, the main characteristics can be summarized as follows: (1) Unequilibrated type‐3 fragments have a well‐preserved chondritic texture with a chondrule‐to‐matrix ratio of ∼1:1. Chondrules and chondrule fragments are embedded in a fine‐grained olivine‐rich matrix. Thus, the texture is quite similar to that of type‐3 carbonaceous chondrites. (2) In all cases, matrix olivines in type‐3 fragments have a significantly higher Fa content (44–57 mol%) than olivines in other (equilibrated) lithologies (38–40 mol% Fa). (3) Olivines and pyroxenes occurring within chondrules or as fragments are highly variable in composition (Fa0–65 and Fs0–33, respectively) and, generally, more magnesian than those found in equilibrated R chondrites.

Agglomerated material of the R‐chondrite parent body (or bodies) was highly unequilibrated. It is suggested that the material that accreted to form the parent body consisted of chondrules and chondrule fragments, mainly having Mg‐rich silicate constituents, and Fe‐rich highly oxidized fine‐grained materials. The dominating phase of this fine‐grained material may have been Fa‐rich olivine from the beginning. The brecciated whole rocks, the R‐chondrite regolith breccias, were not significantly reheated subsequent to brecciation or during lithification, as indicated by negligible degree of equilibration between matrix components and Mg‐rich olivines and pyroxenes in primitive type‐3 fragments.