List of Poster Presentations

NOVEL SAMPLES FOR COSMOCHEMICAL ANALYSIS

Jemma DAVIDSON

Here we report the discovery of a new, novel type of extraterrestrial material available for cosmochemical analysis. Every year, the Earth captures ~40,000 tonnes of extraterrestrial material, much in the form of micrometeorites (MMs) [1]. MMs are submillimetre-sized particles derived from asteroids and comets, which have the potential to provide a record of the flux rate and nature of extraterrestrial bodies over geological time. This material should be incorporated into the terrestrial rock record, but until recently had only been found in Eocene (~40Myr) [2] and Jurassic (~185Myr) [3] sediments. Earlier this year, we reported the discovery of MMs (specifically cosmic spherules) in ~236Myr old halite deposits [4]. These are the oldest MMs found to date and present a new, unique type of sample available to us.

The condition of the spherules recovered indicates reasonable levels of preservation indicating that we could expand our search to encompass unmelted MMs. This would permit detailed comparison of the nature of the cosmic dust flux 236Myr ago with the present day. As orbital lifetimes of Earth-crossing parent bodies are only a few Myrs any difference in sources should be apparent. The spherules have been analysed using optical and electron microscopy and could be subsequently analysed for noble gases, stable isotopes etc, using various analytical techniques including FIB-SEM and NanoSIMS.

We suggest that collection of samples from global salt deposits will yield many more ancient micrometeorites from a large span of geological time, allowing us to build up a record of how extraterrestrial material flux has changed over time.

References:

[1] Bland, P.B. et al., Mon. Not. R. Astron. Soc., 283, 551-565, 1996.

[2] Taylor, S. and Brownlee, D.E., Meteoritics 26, 203-211, 1991.

[3] Czajkowski, J. et al., Meteoritics 18, 286-287, 1983.

[4] Davidson et al., LPSC Abstract, 2007.

Carbonates in the CM chondrite QUE 93005: Mineral chemistry and Mn-Cr systematics

Simone de LEUW

Secondary carbonates in CM chondrites provide evidence of aqueous alteration that occurred in the CM parent body. In this study, we focus on Mn-rich calcite (CaCO3) and dolomite (CaMg(CO3)2) grains that are widespread throughout the fine-grained matrix. Alteration products such as carbonates can potentially provide a record of the timing of aqueous alteration on the parent body. Here we describe chemical characteristics of the carbonates in the highly altered QUE 93005 CM chondrite and initial results of 53Mn-53Cr dating of these carbonates using the high-resolution ims 1270 ion microprobe. Our data and previous studies imply that the degree of aqueous alteration is correlated with the age of carbonate formation and that alteration processes occurred for an extended period of time on carbonaceous chondrite parent bodies.

Characterization of Opaque Phases in Type II Chondrules from CR2 Chondrites

Devin L. SCHRADER

Sulfide assemblages in type II chondrules from CR2 chondrites show evidence for a complex high and low temperature history. This history differs from that of type I chondrules in CR2s. This is the first detailed study of metals and sulfides within type II (FeO-rich) chondrules of CR2 carbonaceous chondrites. The objectives of this study were (1) to characterize the metals and sulfides, (2) to determine the relationship between metals and sulfides in different locations, and (3) to determine the relationship between metals and sulfides of different CR2s. This study is the first reported presence of tochilinite and the highest Ni content of Fe,Ni-rich metal in CR2s. Due to sulfide morphology and composition, the opaque phases possibly formed in gas-solid reactions in the nebula at temperatures above the Fe-FeS eutectic of 988^oC, and then underwent aqueous alteration to various degrees at temperatures from 25^oC to 120^oC.

Search for evidence of high-energy particle irradiation of chondrules prior to parent body accretion

Antoine S.G. ROTH

This research project focuses on cosmogenic noble gases in chondrules in carbonaceous chondrites. In situ measurements of amounts and isotopic abundances of He, Ne and Ar are performed by UV-Laser Ablation Mass Spectrometry (UV-LAMS) in order to recognize possible evidence for chondrule pre-exposure to high-energy particles in the early Solar Nebula. The microdistribution of highly volatile elements in such ubiquitous refractory inclusions provides unique insights into the primeval processes operating in the circumstellar disk from which planets are born.

To date, evidences for pre-compaction exposure of chondrules to cosmic rays are scarce, especially from unequilibrated chondrites with very short exposure ages. Accordingly, three meteorites are selected as suitable samples to reassess the problem: Cold Bokkeveld (CM2) T(21Ne) 0.32 Ma, Isna (CO3) T(21Ne) 0.15 Ma, and Murchison (CM2) T(21Ne) 0.58 Ma.

The potential outcomes of this study are (1) the determination of appropriate techniques both for sample preparation and in situ UV-laser extraction of noble gases in chondrules and matrix, (2) the identification of cosmic ray irradiation of chondrules prior to parent body accretion, (3) the assessment of galactic and/or solar cosmic ray fluences, and (4) the implication of a high-energy particle environment in the inner protoplanetary disk.

Possibility of the compound chondrule formation in the shock-wave heating model

Seiji YASUDA

Chondrules are mm sized, spherical shaped, once-molten particles that are the main inclusion of the chondritic meteorite. There also exists "compound chondrules" in the chondritic meteorite. They are considered to have formed by collision of two independent chondrules (Wasson 1995). Their formation processes are still puzzled because while the percentage of the compound chondrules in all chondrules is 5%, the probability of collision of chondrules is ~10-5.

We notice the heating mechanism of the shock-wave heating model, which is one of the most plausible models for chondrule formation. The relative velocity between gas and dust particle are generated by passage of shock wave and then the dust particles are heated by gas friction. It may be possible to disrupt the melted dust particle due to ram pressure of the fast gas flow (Kadono and Arakawa 2005). Then the number density of chondrules is increased.

We performed three-dimensional thermo-hydro dynamics simulation to simulate disruption of the melted dust particle due to the gas flow and estimated the collision rate of chondrules from calculated ejection rate, velocity dispersion, and size distribution of the fragments. The estimated collision rate is ~1. From this result, we can conclude that it may be possible to form compound chondrules in the shock-wave heating model.

IDENTIFICATION OF SILICATE AND CARBONACEOUS PRESOLAR GRAINS IN THE TYPE 3 ENSTATITE CHONDRITE ALHA81189

Shingo EBATA

Primitive meteorites contain presolar silicate grains that predate the formation of our solar system. In 2006, Ebata et al. have discovered the first evidence of presolar silicate grains from two type 3 enstatite chondrites. Here we report further in situ studies of presolar silicate and carbonaceous presolar grains in the primitive enstatite chondrite ALHA81189.

The samples used in this study are polished thin sections of the ALHA 81189. We surveyed presolar grains by isotopography using a Hokudai isotope microscope system (Cameca ims-1270 + SCAPS). For presolar grain identification, mineralogical and petrographical characterization of matrix areas containing isotopic anomalous grains has been conducted using a FESEM equipped with EDS.

Six of presolar silicates were determined the chemical compositions (Enstatite: 2, Fe-rich pyroxene (En50): 1, Fe-rich olivine (Fo30): 1, SiO2: 1, aggregates of pyroxene-like compositions: 1). The SiO2 and aggregates may be amorphous. In the case of carbonaceous grains, three grains were determined the chemical compositions (graphite: 1, SiC: 2).

Presolar grains of pryroxene compositions are dominant in the enstatite chondrite, whereas olivine, pryroxene and GEMS are equally distributed carbonaceous, IDPs and AMMs. This suggests presolar silicates of enstatite composition were selectively survived in the enstatite parent body.

TEM observations of micro textures in olivine crystals having various lattice strains from a shocked chondrite

Tomoaki AOKI

We observed micro textures in olivine crystals from the Naryilco chondrite by transmission electron microscopy (TEM) after estimating their lattice strains, being obtained from the broadening of reflections in an X-ray powder diffraction pattern. The lattice strains of eighteen olivine crystals were determined and range from 0.075 to 0.278 %. Micro textures in selected four olivine crystals 1, 2, 3 and 4, of which the lattice strains are 0.075, 0.164, 0.170 and 0.250 %, respectively, were observed by TEM. Sample 1 shows small number of linear dislocations mostly directed to [001]. Sample 2 shows medium number of linear dislocations mainly directed to [001]. Sample 3 also shows medium number of linear dislocations, but in which two distinct directions were observed. One of which is [001], but the other is not known. Sample 4 shows large number of curved, interconnected dislocations nearly directed to [001]. The dislocation densities of samples 1, 2, 3 and 4 are 2x108, 32x108, 26x108 and 208x108 cm-1, respectively. This result suggests a linear correlation between lattice strains and common logarithms of dislocation densities of olivine crystals and reveals that the lattice strain obtained by an X-ray method corresponds to the density of dislocations observed by TEM.

Secondary fayalite in the Vigarano CV3 carbonaceous chondrite: Occurrence and formation age

Kaori JOGO

Vigarano, classified to the reduced subgroup of CV3 chondrite (CV3Red), is one of the most primitive materials in the solar system. However, it is known that Vigarano experienced very weak aqueous alteration, which results in secondary fayalite. In this study, I made detailed characterization of fayalites in Vigarano and determined Mn-Cr fayalite formation age.

Petrologic observations indicate that most chondrules have fine-grained rim around them and comprise discrete clasts. Few clasts contain fayalite-bearing veins which terminate at the clast boundary. These results suggest that clasts containing fayalite are Bali-like oxidized material (CV3OxB), which experienced heavier aqueous alteration than Vigarano. While, the preferential occurrence of fayalites in the CV3OxB clasts suggests that fayalite did not form in situ in Vigarano. The Mn-Cr data for fayalite indicates that Vigarano fayalite formed 4561 ± 1 Ma ago induced by aqueous alteration in CV asteroid. The obtained age is identical within errors to that of CV3OxB meteorites. This indicates that the CV3OxB clasts in Vigarano altered in the period same as CV3OxB meteorites.

These results suggest that Vigarano is a breccia consisting of CV3Red and CV3OxB clasts, and CV3OxB clasts in Vigarano derived from different location of the host Vigarano asteroid or different CV asteroid.

Interior structures of gas and ice giants : Heat transfer and the effect of rotation

Yasunori HORI

The sensational appearance of extrasolar planetary systems has stimulated us to construct the framework of the planetary formation systematically, which enables us to give a consistent explanation of origins of a variety of planetary systems including our system. It also makes rapid progress in our understanding of the challenging question. Moreover, the discovery of many extrasolar planets (ESPs) in the past decade presents several remarkable features. As one of them, compiling data on ESPs suggests that most of ESPs can be giant planets of which Jupiter and Neptune are representatives. Properties of giant planets help us reveal their tracks, evolutions and formation processes. However, even our understanding of their interior structures hasn't reached a sufficient level yet. This has encouraged me to concentrate on the study of interior structures of gas, ice giants and ESPs.

I carried out numerical calculations of them which include heat transfer, the effect of rotation and metallic hydrogen. Reviewing the present situation and problems to be solved at first in this poster, I'd like to show the outcome of calculations and discuss abundances of heavier elements in an envelope and mass of solid cores which could trigger the onset of the formation of giant planets.

An outer planet and the origin of Kuiper Belt architecture

Patryk S. LYKAWKA

Trans-Neptunian objects (TNOs) are remnants of an evolved planetesimal disk in the outer Solar System. This complex structure, known as the Kuiper Belt, offers important clues about disk properties and other processes during first stages of Solar System history. TNOs exhibit surprisingly large eccentricities, e, and inclinations, i, which can be grouped into distinct dynamical classes. Several scenarios have been proposed to explain the Kuiper Belt structure, but none has reproduced detailed observations or provided insightful predictions. We propose that the orbital history of an outer planet with tenths of the Earth's mass can explain the Kuiper Belt orbital structure. This massive body was probably scattered by one of the giant planets; then it stirred the primordial planetesimal disk before planet migration. Later, the outer planet acquired a distant and inclined orbit (>100 AU; 30-50 degrees). Our model consistently reproduces the main features of TNOs with unprecedented detail; it also satisfies several other constraints such as the nature of Neptune's migration. The model predicts the primordial planetesimal disk extended to at least ~51 AU and suffered quite an intense collisional grinding before planet migration.

Collisinal Fragmentation Experiments of Gypsum spheres at Low Velocities

Yuichi FUJII

Physical processes of planetary formation from dusts to planetesimals are not well understood. Collision, in particular, low velocity collision, is one of the most important processes in the planetary formation. Collisional outcome varies with critical velocity that is defined as the velocity at which a body begins to break-up. A previous laboratory study of ice spheres showed that the critical velocity is size-dependent at low impact velocity condition (Higa et al.1998). Non-porous ice spheres were used in their experiments. However, dust aggregates have high porosity at least at the very beginning of the planetesimal formation. In order to investigate the collisional process of porous bodies, we performed low velocity collision experiments of gypsum spheres.

In this study, spheres of diameter from 5 to 70mm were impacted against an iron plate and the gypsum block. The impact velocity range was from 0.4 to 22m/s. As a result, we could classify the outcome into 3 types from their appearance. They are intact, fragmentation, and the intermediate state between them. We found that usual excavation cratering process did not occur in the low velocity collision of gypsum spheres. But No clear size dependence was found in these boundary velocities.

Checking contamination for organic analyses in carbonaceous chondrites by micro-FTIR

Yoko KEBUKAWA and Satoru NAKASHIMA

Carbonaceous chondrites are known to contain a few wt. % of indigenous organic matter. Over 70 % of this is present as a complex and insoluble macromolecular organics (e.g. Hayatsu et al., 1977; Pizzarello et al., 2006). Fourier transform infrared (FTIR) spectroscopy is a non-destructive technique for organic components and minerals, and has been successfully applied to chondritic organic matter (e.g. Hayatsu et al. 1977; Murae, 1994; Matrajt et al. 2004). However, carbonaceous chondrites were found to be easily contaminated by organic molecules during sample preparation and storage in laboratory environments. IR absorption bands of aliphatic C-H at 2965 cm-1 and C-O at 1265 cm-1 increased within one day after the pressing of samples between two Al foils for IR transmission-reflection measurements on the Al foil. Hydrous minerals (e.g. antigorite and silica gel) are found to adsorb volatile organic compounds from some plastic containers (plastic tray with silicon rubber) and from some adhesive tapes. Therefore we should avoid the use of these materials during the sample preparation and storage for organic measurements by micro FT-IR.

Infrared and Raman Spectroscopic studies of Antarctic micrometeorites

A. SUZUKI, S. Nakashima and T. Nakamura

We measured IR and Raman spectra of unmelted Antarctic micrometeorites (AMMs) for characterizing organic and hydrous components. Peak positions, FWHM, band intensity ratios (ID/IG) and band area ratios (AD/A(D+G)(%)) for D (defect) and G (graphite) Raman bands were determined and compared with the literature data on carbonaceous chondrites and other cosmic materials. The Raman features of macromolecular carbonaceous materials in the AMMs are similar to those in C1 and C2 chondrites. On the other hand, the AMMs showed IR absorption peaks of H2O, CH3, CH2 and Si-O. The peak height ratios of CH2/Si-O, H2O/Si-O and CH3/CH2 indicate that various types of aliphatic hydrocarbons are present and aliphatic CH2 is richer for higher water contents. These Raman and IR features can be used as indicators for organic evolution during the aqueous alteration.

Composition and origin of Ni-rich spinel from Cretaceous-Tertiary boundary and spinel from meteorite fusion crusts

Ludovic FERRIERE

Ni-rich spinel present in K/T boundary clays is a cosmic event marker, but its formation is still controversial. K/T spinel is characterized by a high Ni2+ and Fe3+ content involving formation in an oxygen-rich environment, and also contains Fe2+, Mg2+, Al3+, and Cr3+ with abundances varying from site to site.

Some of these crystals show a compositional zoning from core to rim, with a core depleted in Fe, Ni, and Ti, and enriched in Cr, Al, and Mg. We found similar zonations in a few spinels from meteorite fusion crusts; zonations originate from incomplete equilibration of primary spinel crystals at subliquidus temperatures (result from the pulse heating experienced by the meteorite during atmospheric entry). A similar origin can be invoked for the compositional zonations observed in impact spinel from the K/T boundary.

The variation of the Fe3+/Fe_total ratio from core to rim may indicate oxygen fugacity increase during crystallization, accounting for reduced chromite precipitation at low oxygen fugacity with subsequent magnetite overgrowth at higher oxygen fugacity. Alternately, it may reflect the presence of relic chromite with subsequent magnetite overgrowth. If so, this excludes a formation by condensation in the impact plume.

Dust Size and Crystallinity around Herbig Ae/Be Stars

Hideaki FUJIWARA

The process of crystallization and grain growth of silicate dust in protoplanetary disks provides key information to link protoplanetary disks with the present-day solar system. Here, we present N-band (8-13 micron) spectra of 58 Herbig Ae/Be stars and the results of spectral decomposition analysis. We extracted spectra of 58 Herbig Ae/Be stars obtained with the Subaru/COMICS, the Spitzer/IRS, and the ISO/SWS. We made compositional model fitting to the spectra by considering five dust species and two dust sizes (0.1 and 1.5 micron) for each of them, and derived the fraction of large grains and the fraction of crystalline silicate grains as indicators of dust evolution. We found that massive, young, or luminous stars with the small value of the large grain fraction do not exist. This trend is explained by the difference in the strength of turbulence in the disk and the radiation pressure on grains, which controls the removal and supply of large grains at the disk surface. We also found that most sample stars show the crystallinity of circumstellar silicate of larger than 5%. On the other hand, no dependence of the crystallinity on the stellar parameters was found. This suggests that dust crystallization has already started in a very early stage of the pre-main sequence before the Herbig Ae/Be phases.

Unusual characteristics and unique secondary process of Ningqiang carbonaceous chondrite

Mitsuhiro SUGITA

In order to find a clue to the characteristics and alteration history of CV3 chondrite, we undertook detailed mineralogical and petrographic study of anomalous CV3 chondrite Ningqiang. We have found that Ningqiang shows unusual characteristics in CAIs and matrix. The CAIs are much smaller in size and lower in modal abundance than those in CV3 chondrites. Most CAIs are porous aggregates of fine grains and melilite grains in them have been extensively replaced by nepheline. The matrix can be divided into two regions: one consists mainly of very fine, equidimensional grains (<1 micron) of relatively Fe-poor olivine, and the other consists mainly of coarse, irregularly shaped grains (2-20 micron) of relatively Fe-rich olivine. In the Fe-poor regions, nepheline occurs pervasively as fine grains, whereas in the Fe-rich regions, nepheline is rare.

The bulk composition of the matrix is similar to mean CV3 matrix for most elements. However, Na and Al are significantly higher (3.6 and 1.8 by factor, respectively). Plots of the analyses of the Fe-poor regions in terms of Na vs. Al show an apparent correlation of the two elements with a slope of approximately Na/Al=1, which suggests that Na and Al can be mainly explained by nepheline (Na2Al2Si2O8).

Textural Characterization of Fe-Rich Phases in H-Chondrites: Structure and Thermal Evolution of the Parent Body

Jeremy GUIGNARD

H-chondrites are samples of a single asteroidal parent body which show evidence for variable degrees of heating. The least "metamorphosed" members of the H-chondrite clan (H3) are mixtures of various components, clearly out of chemical and textural equilibrium. While the mineralogical and compositional effects of progressive heating have been studied in the literature, textural equilibration has received far less attention. We have therefore studied the textural characteristics of metal and sulfide in a series of H-chondrites (H4, 5, 6). These results provide constraints on the structure and thermal evolution of the parent body and have implications for the onset of processes leading to core segregation.

We have quantified: i) metal and sulfide proportions as a function of metamorphic grade; ii) the length of metal-sulfide contacts; iii) dihedral angles at silicate-silicate-metal/sulfide contacts; iv) the shape of metal/sulphide grains (circularity); v) the crystal size distribution (CSD) of metal and sulfide grain populations.

Proportions of metal and sulfide are independent of metamorphic grade, but the length of sulfide-metal contacts decreases significantly with increasing grade (metal and sulfide grains separate). Dihedral angles, grain circularity and CSD's for metal grains show little change between H4 and H5, but show significant changes between H5 and H6. These results may be rationalized in terms of textural equilibration and ripening involving diffusion. Published values for the temperature dependent diffusion coefficient of Fe in olivine have been combined with the results of thermal models describing the temperature-time paths at different depths within a parent body 180km in diameter heated internally by Al26. Comparison of the modelled length scales of Fe-diffusion relative to the average separation of metal droplets implies that the H5 samples come from a depth approximately 30km below the surface, in excellent agreement with independent estimates based upon peak metamorphic temperatures and Pb-Pb dating.

Experimental study on circumstellar crystalline silicates formed by annealing of amorphous precursors

Keisuke MURATA

In order to make clear crystallization process of silicates in circumstellar environments of oxygen-rich stars, we have performed laboratory experiments on crystallization of a silicate material by use of a synthetic sample with the chondritic composition for the first time. The aim of this work is to analyze the crystallization process quantitatively using the amorphous material with the chondritic composition. The starting amorphous material was synthesized by the sol-gel method. The sample was heated to investigate the temperature and time dependence of the crystallization. The run products of the heating experiments were analyzed using infrared absorption spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Olivine ((Mg, Fe)2SiO4) was mainly crystallized from the starting amorphous material. We have performed infrared spectral fittings of the heated samples using individual spectra of olivine and amorphous silicate, and estimated the degree of crystallization quantitatively. The time-dependent crystallization process could be formulated using the Johnson-Mehl-Avrami equation. From the quantitative analyses, we suggest that crystallization processes in protoplanetary disks should depend on properties of the interstellar amorphous silicate precursors such as existence of crystallites and/or FeO-content.

Amino acid distributions of various carbanaceous chondrites

Yoshie NISHIMURA

Amino acid in meteorites is important for chemical evolution and origins of life. In this study, the occurrence of amino acid in eight carbonaceous meteorites of various chondrite type was examined. In addition, degree of terrestrial contamination to amino acid in carbonaceous chondrite were also evaluated.

Yamato (Y)-82162 (CI), Murchison (CM), Y-791191 (CM), Y-82054 (CM), Y-82098 (CM), Y-81021 (CO), Asuka(A)-881595 (CR), and Karoonda (CK) were analyzed using high performance liquid chromatography and gas chromatography-mass spectrometry (GC-MS).

Y-791191 gave a result very similar to that obtained with Murchison, containing not only protein amino acid but also nonprotein amino acid. D/L ratio for aspartic acid, glutamic acid, alanine, and valine in Y-791191 was higher than that in Murchison. These results indicate that Y-791191 is less contaminated than Murchison. Other CM chondrites, Y-82054 and Y-82098, yeilded only few amino acid. Therefore, it is suggested that amino acids are not always abundunt in all CM chondrites. Glycine was the most abundant amino acid in Y-82162 (CI) and Karoonda (CK). In Y-81021 (CO), beta-alanine was the most abundant. A-881595 (CR) was devoid of indigenous amino acid. So amino acid distribution in various carbonaceous chondrite could partly reflect alteration histories on each meteorite parent body.

Small shock-induced melt veins in matrix, CAIs, and chondrules in the Efremovka CV3 chondrite

Kaori IINUMA

Most carbonaceous chondrites have been affected by minor degree of shock metamorphism (from shock stage S1 to S3), which contrasts with ordinary chondrites that show various degrees of shock metamorphism up to S6. The difference in shock response between these two types of chondrite probably resulted from the difference in modal abundance of porous matrix. Efremovka is a CV3 carbonaceous chondrite that shows shock effects classified into S4. We studied thin sections of Efremovka, and found many small shock-induced melt veins in various locations: matrix near chondrules, matrix near CAIs, and chondrule mesostasis. The melt veins near CAIs have very high Ca and Al contents and show a gradual decrease in Ca and Al contents, as they go away toward the matrix. We interpret that the melts are a mixture of melted matrix and CAI minerals, and they resulted from frictional heating due to displacement along fractures. The formation mechanism is probably analogous to that for pseudotachylites. The melts in the matrix are similar in composition to the matrix and homogenous. They probably formed as a result of very locally melting process. Therefore, it's thought that generation of local melt is an important key in shock metamorphism of carbonaceous chondrite.

Occurrence and origin of igneous fragments in chondritic breccias

Anna K. SOKOL

The ordinary chondrite breccias Adzhi-Bogdo (LL3-6) and Study Butte (H3-6) contain igneous-textured inclusions that are best described as alkali-granitoids in Adzhi-Bogdo and andesite in Study Butte. Both the granitoids and the andesite appear to have been formed by melting and magmatic differentiation on a parent body and indicate mixing of achondritic fragments with chondritic components.

Al-Mg isotope data for these igneous-textured clasts reveal no evidence for radiogenic 26Mg and indicate that the formation of these igneous clasts, the incorporation into the parent body regolith, and the lithification must have occurred late, after almost all 26Al had decayed.

On a three-O isotope diagram all fragments fall in the range of ordinary chondrites. These results imply that the fragments derive from an ordinary chondrite precursor and may have formed on the same parent body as the surrounding host rock material. This in turn indicates that melt formation and extreme differentiation occurred on ordinary chondrite parent bodies in the early stage of solar solar system formation. Alternatively, the fragments may have formed on another parent body but within the same oxygen isotope region of the solar nebula. In this case, they may represent projectile fragments within the chondritic breccias.

Evolution of Chondrule formation: Constraints from 26Al ages and Cosmochemical properties

Erika KURAHASHI

To get better understanding on the origin of chemical group of chondrites, I have conducted systematic investigations of formation age, chemical compositions, mineralogical characteristics, and bulk chemical compositions of chondrules in a primitive CO3.0 Yamato-81020. I found concurrent formation of chondrules between CO (1.3-2.4 Myr after CAIs) and LL (1-2.5 Myr in literatures) chondrites using SIMS. CO Type II chondrules are tend to be slightly younger ages (2.0 Myr~). The simultaneous formation of chondrules of CO and LL chondrites suggest that the chemical differences between CO and LL chondrites might be caused by spatial distinction of their chondrule formation environments in the protoplanetary disk.

The similar formation age of chondrules in LL and CO chondrites, later generation of Type II chondrules compared to Type Is in Y-81020, and larger abundance of Type Is in CO chondrites than LL chondrites are modeled by taking the stability of silicate, organic materials and ice, temperature evolution of the nebula, and plausible physical process of chondrule formation into consideration.

Mineralogical analysis of the Tagish Lake carbonaceous chondrite by X-ray diffraction and Rietveld refinement

Matthew R. M. IZAWA

The Tagish Lake carbonaceous chondrite (C2 ungrouped), which fell in northern British Columbia, Canada, in January 2000, has since been the subject of intense and diverse research. However, there have been few analyses of the abundances of individual mineral phases. We present an investigation of the mineralogy of Tagish Lake using X-ray diffraction (XRD). X-ray micro-diffraction was used for initial reconnaissance. High resolution powder XRD data was collected in order to determine modal mineralogy via Rietveld refinement, a well established technique for the quantitative analysis of multiphase mixtures. This technique has not previously been applied to bulk meteorite samples, but has great potential value. Quantitative mineral abundances are often difficult to obtain directly, thus modal abundances of individual phases in meteorites are often poorly constrained. The modal analysis is as follows (all values in weight percent): saponite 55 ± 2 %, olivine (Fo100) 11 ± 1 %, olivine (Fo90) 11 ± 1 % , siderite 8 ± 1 %, magnetite 7.0 ± 1 %, clinoenstatite (En94Wo4) 3.3 ± 0.4 %, pentlandite 1.7 ± 0.4 %, calcite 1.7 ± 0.4 %, pyrrhotite 1.1 ± 0.9 %.

Detection of rare CO isotopologues in a protostellar disk: using astronomical data to investigate molecular self-shielding in the early solar nebula

R. L. Smith, E. D. Young, M. R. Morris and K. M. Pontoppidan

We report detection of four stable isotopologues of carbon monoxide (CO), including the rare species 12C17O, in protostellar object IRAS 19110+1045. Our study centers on using astronomical data to investigate the phenomenon of molecular self-shielding by CO in protostellar disks around young stellar objects - environments believed to be similar to the early solar nebula - as a possible explanation for the oxygen isotope anomaly in the solar system. Referring to the saturation of photodissociating spectral lines for optically thick molecular species, molecular self-shielding is a known phenomenon in the interstellar medium but as yet has not been reported with certainty in protostellar disks. Using archival NIRSPEC (Keck II) data, we obtained column densities for CO using a linear spectral relation for optically thin molecules (12C18O, 12C17O) and a curve of growth analysis for optically thick species (13C16O,12C16O). Solar abundance ratios were found, contrary to implications from a previous study by Brittain et al. (2005). While preliminary, our results indicate that it is possible to detect rare CO isotopologues in the near-infrared. While we see no evidence for isotope-specific photodissociation of CO in the data reported here, in-depth analyses are currently underway using more precise data sets obtained with our specific goals in mind.

Mineralogy and petrology of Northwest Africa 1232: a brecciated CO carbonaceous chondrite

Miho KIRIISHI

Northwest Africa (NWA) 1232 is an unusual CO3 chondrite which has two different areas (termed dark area and gray area). I observed and analyzed this chondrite by using optical microscope and SEM-EDS, and found that these two areas have the different degree of thermal metamorphism.

In the gray area, most olivine phenocrysts in type I chondrules are Fe-rich and the chemical composition is homogeneous. Mean composition of olivine is Fa32. On the other hand, in the dark area, most olivine phenocrysts in type I chondrules are Mg-rich and show Fe-Mg zoning. Mean composition of olivine is Fa12. These results suggest that the degree of thermal metamorphism in the gray area is higher than the dark area. In addition, I found some unusual clasts in the dark area. These are composed of matrix, CAIs or chondrules. The matrix is fine-grained and unequilibrate. The CAIs and the chondrules show no effects of thermal metamorphism and metasomatism. These features resemble CO3.0. These results suggest that the CO parent body was considerably heterogeneous and experienced more complicated brecciation process.

Onset and duration of chondrule formation in the early solar system using Al-Mg isotope systematics

Rudraswami N. GOWDA

Al-Mg isotope records in nearly thirty ferromagnesian chondrules from nine unequilibrated ordinary chondrites (UOCs), four L-chondrites, one L/LL chondrite, four LL chondrite with petrologic grade 3.0 to3.3 were studied using an ion microprobe to look for presence of now-extinct nuclide 26Al at the time of their formation. UOCs of low petrologic grades were selected to avoid possible thermal perturbation of Al-Mg isotope records in the analyzed chondrules. Presence of resolved 26Mg excess in Al-rich phases, such as glassy mesostasis and plagioclase, was found in all the chondrules, barring a sole exception. Majority of the chondrules have initial 26Al/27Al ratio in the range (0.5-1.2)x10-5. Our data supports a late formation of chondrules relative to CAIs, suggested in previous studies, and indicates a time lag of at least 1.5 Ma between CAI formation and onset of an intense episode of chondrule formation in the early solar system that lasted less than a million years. The paucity of chondrules (<10%) with initial 26Al/27Al >1.2x10-5 rules out active chondrule forming events at earlier epochs. The presence of rare chondrules with initial 26Al/27Al <5x10-6 in UOCs of low petrologic grades (3.0 to 3.3) analyzed by us and also reported previously in UOCs of petrologic grade ranging up to 3.4, most probably represent parent body processes leading to disturbance of Al-Mg isotope systematics in these cases. An extended duration of chondrule formation lasting more than a couple of million years, suggested in some earlier studies, needs reassessment. A long duration of chondrule formation is also difficult to reconcile with the problem of storage, isolation, mixing and assimilation of chondrules into their meteorite parent bodies.

Fe-alteration of Spinel in a Fine-grained CAI from the Efremovka CV3 Chondrite

Daiju KASHIMA

This study focuses on the formation of Fe-bearing spinel in a fine-grained CAI (FGI-12) from the CV3 chondrite Efremovka. During previous work [1], variations in Fe-abundance of spinel were noted in this CAI; however, the compositional range of spinel composition was not determined. The goal of this study is to determine controls on spinel composition in FGI-12 from a systematic survey of spinel location and Fe/(Fe+Mg). The occurrence and composition of spinel grains from FGI-12 were compared with those of an adjacent coarse-grained type B1 CAI. In both CAIs, the Fe-rich spinel grains tend to occur near the edge of the CAI rim, suggesting that FeO-alteration occurred after CAI formation. The higher FeO-contents of FGI-12 spinel (<9 wt.%) are probably due to the greater porosity of this CAI. Fe-bearing spinel can form in the nebula if dust-enrichment is high. But this process should produce Cr-rich spinel [2], which was not observed. We infer that the Fe-alteration of spinel occurred after incorporation of the CAIs into the Efremovka parent body.

References: [1] Fagan T.J. et al., 2004. MaPS, 39: 1257-1272. [2] Ebel D. and Grossman L. 2000. GCA, 64:339-366.

Lithium Isotope Analyses of Pyroxene Crystals from the Eucrite Meteorite Pasamonte

Karen D. RIECK

Zoned pyroxene crystals in the eucrite meteorite Pasamonte indicate a history of chemical and thermal disequilibrium. Lithium zoning patterns provide evidence of subsolidus modification (Herd et al., 2004). Because 7Li diffuses more slowly than 6Li, initially isotopically homogeneous grains may become zoned as lithium concentrations attempt to diffusively equilibrate during subsolidus cooling. Such isotope ratio variability may be used to infer cooling rates (Beck et al., 2006) on the eucrite parent body. Here we present the first data on lithium isotope ratios in Pasamonte pyroxenes for such a purpose. δ7Li in pyroxene crystals from two clasts were measured with Cameca IMS 3f and 6f SIMS revealing intra-clast and inter-clast homogeneity. The maximum variation within any pyroxene crystal was ~ 4‰. This is consistent with either rapid quenching, or a long period of slow cooling and equilibration. However, δ7Li (calibrated against basaltic glass standards) appears to be 10 to 20 ‰ heavier in pyroxene than in plagioclase or in the brecciated matrix. These marked differences might be produced by subsolidus alteration because of faster lithium diffusion in plagioclase verses pyroxene, however, further studies of matrix effects in SIMS and major element zoning in pyroxene are needed.

Ca, Al-rich inclusions in Rumuruti Chondrites

Surya S. ROUT and Addi BISCHOFF

Rumuruti chondrites (R-chondrites) are a group of chondritic meteorites that are highly oxidised, olivine-rich (~Fa39), and have high 17O values. Here, we present the results of our analysis of Al-rich objects. During systematic search we detected 116 Al rich objects within 16 R-chondrites. Based on mineralogy and texture the Al rich objects can be subdivided into 7 groups.

(1) Concentric spinel-rich inclusions (36). These CAIs have abundant spinel and based on the presence/absence of major different phases can be subdivided into three groups: (a) concentric spinel-rich (17), (b) concentric spinel-fassaite-rich CAIs (7), (c) concentric spinel-rich CAIs with abundant Na-, Cl-rich alteration products (12).

(2) Concentric hibonite-rich CAIs (2).

(3) Concentric fassaite-rich CAIs (3 spherules).

(4) Complex spinel-rich CAIs (51): Based on their mineralogy these CAIs can be subdivided into four subgroups: (a) complex spinel-hibonite-rich inclusions (2), (b) complex spinel-plagioclase-rich CAIs (26), (c) complex spinel-fassaite-rich inclusions with abundant Na- and/or Cl-rich alteration products (16), (d) complex spinel-rich CAIs with abundant Na-,Cl-rich alteration products (7).

(5) Complex diopside-rimmed CAIs with minor fassaite and/or alteration products (3).

(6) Al-rich chondrules (19).

(7) Al-rich fragments (2).

Mineral alteration of type B1, B2, and fluffy type A Ca-Al-rich inclusions from the Allende CV3 chondrite

Yu TASAI

This study focuses on secondary alteration of CAIs from the CV3 chondrite Allende. In this study, modes of primary and secondary minerals were determined for one Type B1, one Type B2 and one Fluffy Type A (FTA) CAI in Allende.

Two methods were used to determine modes. One method is based on manually counting the cross-points on a grid lain over back-scattered electron (BSE) images. Many secondary minerals have similar dark appearance in BSE; they were grouped together as "BSE-dark" and were identified subsequently using energy dispersive spectroscopy. The other method is based on elemental maps and a remote sensing program. Elemental maps were collected by electron microprobe, and minerals were identified based on their characteristic composition.

Grossular-rich and feldspathoid+feldspar-rich alteration patches and veins were identified in each CAI, but modal abundances and textural occurrences vary. Over 50% of the FTA CAI has been replaced—mostly by the felspathoid+feldspar-rich alteration minerals. The grossular-rich alteration domains are more common in the type B CAIs, although the type Bs have not been altered as extensively as the FTA. These results indicate that some alteration occurred prior to parent body formation and/or alteration conditions varied locally within the Allende parent body.

Ca and Ti isotopic ratios in high-density graphite grains from Orgueil

M. Jadhav, S. Amari, K. K. Marhas, E. Zinner, T. Maruoka, and R. Gallino

We present NanoSIMS C, N, O, Si, Al-Mg, K, Ca and Ti isotopic analyses of high-density graphite grains from Orgueil. Our results indicate that contrary to previous conclusions, high-density graphite grains from Orgueil seem to have multiple stellar sources. A supernova origin for four of the grains is clearly indicated by the presence of ^44 Ti in them. Some grains exhibit extreme Ca and Ti anomalies. Such high Ca and Ti isotopic ratios are not seen in the envelopes of AGB stars but appear to be pure nucleosynthetic components from the He-shell. Some of these grains also have ¹²C/¹³C ratios ~ 4 which are unusual in grains that exhibit large excesses in the s-process elements like, Ca and Ti. This study leads us to conclude that high-density grains come from Type II SNe, low-metallicity AGB stars and probably, born-again AGB stars like Sakurai's object.

Further, it is unclear why high-density graphite grains from Orgueil seem to retain almost pure nucleosynthetic components in Ca and Ti, but are isotopically normal in N, O, Mg and Si isotopes.

Thermal evolution of the terrestrial planets

Chihiro TACHINAMI

Recently, numerical simulation of Planetary Formation Theory and observation indicate that the massive terrestrial planet, "Super Earths" ,should be exist in the extra solar system.In this study, we consider the interior structure and the thermal evolution of such exoplanets,.Thermal evolution of the planet will be related to the exist of the intrinsic magnetic field of the planet. We structed the models for the calculation of internal structure and thermal evolution of the planets.

For the calculation of the internal structure, we adopted the third-order Birch-Murnaghan EOS and hydrostatic equilibrium.The method calculates the one dimensional distribution of density and pressure, gravity acceleration.The results is used for the initial condition of the calculation of the thermal evolution of the planet.

For the thermal evolution ,we calculate the evolution of the one dimensional temperature distribution of planet's interior using the equation from Mixing Length Theory.

We calculated the thermal evolution of the terrestrial planets that have the various mass. Result is that viscosity increase will be so effective as the planet's mass increase that the planet cannot cool because the ability of thermal trancepor of the mantle is dominated by viscosity.Thus, the "Super-Earth" could not have the its intrinsic magnetic field.

Short Lived Radioactivities in the Early Solar Nebula

Allen L. PARKER

Explaining how our Solar System formed is a challenging task. We must discover the necessary formation preconditions by studying the present day abundances of the Sun and meteorites. Meteorites and small grains give us "snap shots" of the abundances present at the time of formation. These "snap shots" show us that there were short lived radioactive species present in the early solar system because the daughter nuclei are enriched with respect to steady state abundances.

In this poster I will discuss the presence of short lived radioactive species with an emphasis on a late injection from a supernova. Also, I will describe computational resources we have developed, and will make available at http://www.webnucleo.org  , to explore this topic and our recent work in this area.

Effects of hydrogen on limits of radiative emission from a planet with a saturated-water-vapor atmosphere

Miki NAKAJIMA

It is known that there are upper limits of radiative emission from a planet covered with sufficient water. If incoming thermal flux exceeds the limits, extra thermal energy is used to evaporate the ocean, which means that an ocean is unable to exist under such a circumstance.

These limits have close relationships with the early evolution and habitability of planets. Since the energy flux from the planet's surface decreases with time, the limits constrain the timing of ocean formation. Moreover, because the stellar radiative flux decreases with distance from the star, this limits constrain the inner edge of the habitable zone. Several studies investigated these limits (e.g., Kasting et al. 1988; Nakajima et al. 1992). However, no study has evaluated the effects of hydrogen on these limits. According to recent studies, the initial Earth is likely to have been rich in hydrogen (e.g., Ikoma and Genda 2006). Furthermore, in extrasolar planetary systems, there might exist hydrogen-rich terrestrial planets.

We have investigated the effects of hydrogen and gravity on the limits by simulating the atmospheric structure in the radiative-convective equilibrium. Then we discuss the early evolution of the Earth and the location of the habitable zone in extrasolar planetary system.

Formation of terrestrial planets around M dwarfs

Masahiro OGIHARA

In the past about 10 years, over 200 extrasolar planets have been discovered mainly with spectroscopic radial velocity survey. Most of these planets are found around solar-type star, because low-luminosity stars such as M dwarfs are disadvantageous for spectroscopy. However, M dwarfs account for about 70-80% of the galaxy disk, so that discovery of planets around M dwarfs will keep increasing with the improvement of observational technique.

We have investigated the accretion of terrestrial planets from planetesimals around M dwarfs through N-body simulations. Because of low luminosity of M dwarfs, their habitable zones are located near central stars. Accordingly, the formation of terrestrial planets around M dwarfs would differ from that around G dwarfs in some perspectives.

For example, the terrestrial planet regions are located near the inner edge of protoplanetary disk. Planetary embryos embedded in a gas disk suffer a decay in semimajor axis (type I migration). However, when the embryos migrate inside the disk inner edge, the effect of type I migration diminishes. As a consequence, planets would pile up near the edge, and this would influence how terrestrial planets form and evolve.

Experimental formation of organic particles on silicate surfaces for simulating organic globules in carbonaceous chondrites

Taku IWAMOTO

In order to simulate the formation processes of organic globules found in the Tagish Lake meteorite (ungrouped type 2 carbonaceous chondrite fallen in 2000), a series of hydrothermal heating experiments of an OH-bearing amino acid (threonine: Thr) have been conducted in the presence of some rocks (rhyolite, basalt). 40 ml of Thr solution with a rock piece was heated in a hydrothermal vessel at 160oC for 4 days. Spherical particles of 2 to 20 micrometers in size were observed under Scanning Electron Microscope (SEM) on the both rock surfaces. The average diameter of the spherical particles increased from 1.0, 2.5 to 4.7 micrometers for 1, 2 and 3 days of heating at 160 oC on the rhyolite surface. By elemental analyses of the particles, they are found to be carbon rich substances. Infrared spectra on these particles showed the presence of aliphatic C-H bonds. These results suggest that organic particles can be formed by the interaction of organic solutions with silicate surfaces during the aqueous alteration of the chondrite parent body.

Radial transport of H2O and silicate in an accreting protoplanetary disk : On the effect of variation in adhesive properties between H2O ice and silicate

Takashi FUKUI

Oxygen isotopic heterogeneity among chondritic constituents (16O-rich CAIs and 16O-poor chondrules) reflects evolution in oxygen isotopic composition of the inner solar nebula gas. Yurimoto and Kuramoto (2004) have suggested that the oxygen isotopic evolution at the inner nebula was induced by subsequent enhancement of 16O-depleted H2O which produced by photochemical process in the parent molecular cloud. In their model, the excess H2O was supplied from outer part of the nebula with inward migration of ice-covered dust particles and evaporation of the icy mantle. However, they did not consider migration of silicate dust particles which apparently result in depletion of chondrule precursors. In this study, we perform a numerical simulation of radial transport of H2O and silicate in an accreting protoplanetary disk considering difference in adhesive properties between H2O ice and silicate. As a result, sticky ice-covered dust particles grow up to ~cm and efficiently migrate inward excess water vapor to the inner nebula, while small (~sub-mm) silicate particles are well coupled to the gas and retained in the inner nebula over ~Myr.

Two preliminary studies for the investigation of stable isotopic variations of REEs in chondrites and their components

Shigeyuki WAKAKI

My study is focused on the isotopic characteristics of rare earth elements (REEs) in chondrites and their components. REEs are group of lithophile refractory elements. Isotopes of REEs in chondrite components are likely to be fractionated during high-temperature process in the early solar nebura. I will show two preliminary results of the ongoing study.

REE composition of Allende CAIs

REE compositions of ninety CAIs in the Allende (CV3) meteorite are determined by INAA. Six coarse-grained inclusions and 30 fine-grained inclusions show fractionated REE patterns (group II). Two sub types of group II can be distinguished by means of Eu, Yb and Lu abundances. Nineteen coarse-grained inclusions and 9 fine-grained inclusions show un-fractionated REE patterns (group I, III, V, VI). Six coarse-grained inclusions and 20 fine-grained inclusions show un-fractionated REE patterns with relatively low REE abundances (< 10 x CI).

Development of a technique for stable isotope measurement of Nd

I have developed a technique for high-precision Nd stable isotopic ratio measurements by double spike TIMS method. Both mass-dependent and mass-independent fractionations in Nd isotopes are measurable by the technique. Igneous rock samples analyzed so far show no variation in Nd stable isotopic compositions, while mass-dependent stable isotopic variations are found in some terrestrial carbonates.

Development of CO2 laser - BrF5 fluorination system for analysis of oxygen three isotopes and application to classification of meteorites

Insoo AHN

For quantitive analysis of oxygen isotopes from silicates and oxides a few fluorination techniques were developed. In the present an analytical system for precise measurement oxygen three-stable isotopes has been installed at Korea Polar research institute(KOPRI) and it is CO2 laser - BrF5 fluorination system connected on-line to a high precision mass spectrometer. Nowadays, we are analyzing oxygen isotopic ratios (17O/16O and 18O/16O) of some terrestrial reference samples for standardization of the system.

Evaluation of captured micrometeoroid analogs by aerogel at the flyby speed of STARDUST

Kyoko OKUDAIRA

Aerogels are excellent capture media for hypervelocity particles but are excellent thermal insulators as well. Hence there is a possibility that heat converted from kinetic energy of a captured particle might thermally alter the particles. It is essential to evaluate such physical changes of captured particles during the capture process for better interpretation of space mission samples. Accordingly, some physical alterations of particles on capture by aerogel at 2 - 6 km/s are assessed. Simulating the hypervelocity capture, analog particles (serpentine and cronstedtite) were fired into aerogel (0.03 g/cm3). After the shots, captured particles were analyzed by several methods. Estimates of survivability S of particle volume and simple energy partition in the capture is mainly discussed here. It is estimated that in the case of serpentine the median S is 21 %, while cronstedtite shows 22 % at 6 km/s. Assuming that the mass loss is due to ablation alone, this requires 17 % (serpentine) and 11 % (cronstedtite) of the impact kinetic energy at 6 km/s. Large fraction of each particle is lost, but still its inner part is retained mineralogically intact, which would be the implication for STARDUST samples, although there seem no phyllosilicate minerals so far.

Hydrodynamics of Molten Chondrules in Gas Flow and Comparison with Their Observations

Hitoshi MIURA

The shock-wave heating model is one of the most plausible models for chondrule formation. In this model, the molten chondrule precursor dust particles (droplets) are exposed to the high-velocity gas flow. It causes various hydrodynamic behaviors, e.g., internal flow, deformation, fragmentation, and so forth. Their hydrodynamics is very important to explain the physical properties of chondrules (three-dimensional shapes, size distribution, etc.). We carried out the three-dimensional hydrodynamic simulations of molten droplets and applied these results for the chondrule formation in the framework of the shock-wave heating model. Our results meet some observational constraints for chondrule formation (e.g., maximum size, prolate-shaped chondrules measured by X-ray tomography, etc.). In addition, our hydrodynamic simulations have great potential to investigate internal structures of chondrules and other observational features. I will introduce our recent results and would like to discuss the applications of our hydrodynamic simulation for chondrule formation.

Identification of Minerals by Raman Spectroscopy from Hypervelocity Impacts on Stardust Grade Foils

Nick FOSTER

Raman spectroscopy offers us an excellent technique for the identification minerals due to molecules giving a unique Raman spectra or chemical "Fingerprint". Raman spectroscopy also requires no sample preparation, and is on the whole non-destructive, giving us a valuable tool in the chain of analysis technique that will be used on samples returned from Stardust.

By recreating hypervelocity impacts onto Stardust grade Al foils in the laboratory using the University of Kent's Light Gas Gun (LGG) we can mimic the impact processes involved when Stardust pasted through the coma of comet Wild/2. Samples were produced by firing suitable projectiles such as olivine, rhodonite, diopside, enstatite, etc at a velocity of 6.1 km/s on to Al 1145 foil. These foils were them imaged using electron backscattering in a Scanning Electron Microscope and overlaid with a Energy Dispersive X-ray map to highlight the most potential craters for Raman spectroscopy. Mineral spectra were obtained within 10 minutes of scanning on most craters.

Therefore Raman spectroscopy has been proved to be a valuable tool for the early stages of analysis of samples returned from NASA's Stardust mission.

Formation model of fine-grained rims surrounding chondrules, CAIs and forsterite-rich aggregates in the Tagish Lake carbonaceous chondrite: Parent-body alteration

Akiko TAKAYAMA

It is widely believed that fine-grained chondrule rims were formed by accretion of the hydrous nebular dust. Greshake et al. (2005) suggested that fine-grained rims in Tagish Lake were also formed pre-accretionary by nebular dust. However, we found several evidence which against this conclusion. Instead, we suggest their formation entirely by parent-body processes. Within the optically opaque matrix are embedded 84 chondrules, one CAI and 14 forsterite-rich aggregates. 97 % of these large components are surrounded by thick (<220 mm), fine-grained rims. These rims consist mainly of phyllosilicates and minor amounts of Fe-Ni sulfides, magnetites, carbonates and olivine and are distinctly less porous than the surrounding matrix. Another noteworthy feature of the rims is the general presence of radial cracks which never go through the matrix. 69% of the chondrules contain pseudomorphs of the phenocrysts embedded within the rims. We found 57 clasts which seem to be fragments of chondrule rim judging from their texture, mineralogy and chemical compositions. From these results we suggest that chondrules in Tagish Lake were replaced by phyllosilicates on their parent body preferentially from their surface, where we now see as fine-grained rims. Secondary they were fragmented and transported to the present location.

Experimental Study of the Impact Cratering Process in the Strength Regime

Kensuke HIRAOKA

A strength-dominated cratering on brittle materials depends on target compressive and tensile strength. We performed impact cratering experiments on sintered glass bead-silicate mixture targets and measured compressive and tensile strength uniaxial compression and Brazilian test, respectively. The compressive and tensile strength of sintered glass bead-silicate mixtures increase with silicate content. The crater on higher silicate content is smaller than that on lower silicate content. We compared the result of ice-silicate mixtures, sintered glass silicate mixtures and some previous works. The results depend on the target porosity. This is probably the effect of shock attenuation rate related to target porosity.

Aqueous altration process of the rims in the CM carbonaceous chondrites

Makoto MAEDA

Fine-grained phyllosilicates occur as rims enclosing chonsrules in the CM carbonaceous chondrites. Many scientists think that the rims formed in the solar nebula by accretion of dust onto surface of chondrules (e.g. Metzler et al. 1992). Thus, many scientists think that the rims are most primitive materials which keep information of the solar nebula. But, CM chondrites have experienced aqueous alteration on the parent body.

Three CM carbonaceous chondrites Y791198, Cold Bokkeveld and Nogoya were investigated by a scanning electron microscope equipped with an energy dispersive X-ray spectrometer. The results show that mineral composition and chemical composition of rims make homogeneous with increasing alteration. Thickness of rims and diameters of corresponding chondrules change with increasing alteration. Thickness of rims increase with alteration progress, diameters of corresponding chondrules decrease with alteration progress. These results indicate that textures and chemical compositions of rims change with alteration progress. Therefore, to obtain information of the solar nebula, I believe that to investigate least alteration samples is the most important.

Prolate Cosmic Spherule Formation

Masao DOI

Cosmic spherules are extraterrestrial-origin objects collected from the stratosphere, polar ice, and ocean floor sediments. They are less than 1 mm in size. Some cosmic spherules have prolate shapes, though the origin of the prolate shape is not known yet. In this study, 1) we obtained an analytic solution for the shape of the molten particle under the gas ram pressure and 2) calculated the motion and temperature of the dust particle entering the atmosphere to evaluate the magnitude of the ram pressure acting on the dust particle when it solidifies. In this calculation, the decrement of the size by evaporation is taken into account. Furthermore, we estimated the torque caused by the asymmetry of the particle shape, and obtained the angular velocity of the dust particle. We examined cases for a wide variety of entry parameters: the initial radius ranges from 5 micron and 1 mm, the entry velocity ranges from 11.2 km/s and 30 km/s, and the entry angle ranges from 0 and 90 degrees (the angle 0 corresponds to the zenith direction). As a result, it seems highly likely that some dust particles that have proper entry parameters form prolate cosmic spherules.

Setting of Equilibration in EH Chondrites

Sho KATAOKA

The purpose of this study is to distinguish equilibration processes before and after EH parent body formation based on correlations between chondrule types (texture and mineralogy), mineral abundances and silica polymorphs using petrographic microscope, electron microprobe, and Micro-Raman spectroscopy. We examined four following EH3 chondrites: ALHA81189, ALH 84170, PCA 82518 and MET 01018 and one EH5: St. Marks.

All samples can be classified in the following three groups based on chondrule type and Raman spectra, (1) St. Marks (EH5); (2) ALHA81189 (EH3); and (3) the other EH3 chondrites. Differences between group (1) vs. (2) and (3) were caused by parent-body metamorphism of St. Marks. The recrystallized chondrule boundaries and the presence of quartz as the only silica polymorph are consistent with equilibration during parent-body metamorphism.

We can identify distinct differences between (2) and (3) due to different pre-parent body effects. Groups (2) and (3) are composed of different types of chondrules. Chondrules in ALHA81189 have more olivine phenocrysts and more silica-rich rims than chondrules in other EH3s, indicating formation from different precursors or different extents of gas-solid reaction during chondrule formation. Parent-body metamorphism does not account for the differences between these two groups.

Petrography of Yamato-791088, a partial melt rock of H chondrite

Takafumi NIIHARA

Most chondrites have not been heavily shocked and impact melt rocks are very rare, although all of ordinary chondrites have experienced some shock effect. *Stoffler et al. (1991) classified shock stages into S1-S6 and "melted". We investigate an H chondrite of Yamato-791088 classified into "melted". The purpose of this study is to describe it in detail in order to clarify dynamic impact event at the parent body and its thermal history.

The major phases of Yamato-791088 are olivines, pyroxenes, Fe-Ni metals, sulfides and glassy phases. Minor phases are spinels and phosphates. Variations of grain sizes are large from about submicron to milli-meter. Textures are microscopically divided into two area, relict and melt. Constituent minerals commonly occur in two areas. However, they have different shapes and compositions.

Relict minerals show irregular shapes and have homogeneous composition. On the other hand, crystallized minerals from impact melt show euhedral shapes surrounded by glassy phases, and have heterogeneous composition. Fine grained oligoclases occur coexisting with albitic-glass in melted area. We conclude that the impact heating of Y-791088 heterogeneously occurred and cooling after the heating was rapid. The occurrence of oligoclases should constrain the rapid cooling rate.

*Stoffler D. et al. GCA, 55, 3845-3867 (1991).

CHEMICAL COMPOSITION AND FORMATION PROCESS OF SILICA-RICH CHONDRULE RIMS IN THE SAHARA 00182 CR/CV CHONDRITE

Yuki KAKAZU

We found silica-rich rims that constitute the outermost layers around type I chondrules in the Sahara 00182 CR/CV chondrites. The rims contain a high abundance of silica phases. It is known that in the equilibrium condensation process, silica couldn't appear in the solar nebula. In order to obtain a better understanding on the formation of silica-rich rims.

The silica-rich rim consists of silica, low- and high-Ca pyroxene, Fe,Ni-metal, and no olivine.

We obtained bulk composition of the chondrule core and the silica-rich rim.The compositions, normalized to Mg and CI carbonaceous chondrite. The silica-rich rim is enriched in Ca, Al, Ti, Si, Cr, Mn, Na and K and depleted in Fe, Ni and S relative to CI.

Oxygen isotope ratio for silica exhibits from -6 to 22 ‰ in δ18O and from -8 to -1 ‰ in δ17O.

The average of REE abundance in the silica-rich rim are close to the solar abundance and did not fractionate.

These facts indicate that the silica-rich rims formed by accretion and subsequent melting of 16O-poor, REE-unfractionated silica-rich dust onto normal type I chondrules. Currently, it is uncertain how such silica-rich dust formed in the early solar nebula.

Hydrothermal alteration experiments of amorphous silicates

Ryo NOGUCHI

Carbonaceous chondrites are the most primitive meteorites. Among them, CI, CM, CR and TL chondrites experienced strong aqueous alterations on their parent bodies. Therefore, a study of the alteration process is important for understanding the evolution of early solar system materials. To investigate the aqueous alteration process, many hydrothermal experiments have been performed so far using crystalline silicates or chondrites themselves. On the other hand, slicate in molecular cloud is considered to be amorphous based on IR astronomical observations. Therefore, it is important to investigate the aquous alteration of the amorphous silicates.

In order to understand the aqueous alteration process of amorphous silicates, we have carried out hydrothermal alteration experiments of synthetic amorphous silicates with the CI chondritic composition. The starting material was synthesized by the sol-gel method. A mixture of the starting material and deionized water (or acid/alkali solutions) was heated at 150oC for 1 week. Run products were analyzed using XRD and SEM-EDX. Saponite-like phase was easily formed from amorphous silicates. Serpentine was formed from olivine which were prepared from amorphous silicates preheated at 750oC for 20hours. Calicte was also formed.

TEM STUDIES OF SILICON CARBIDE IN PRESOLAR GRAPHITE

Kathryn Mairin HYNES

Equilibrium condensation models for AGB stars predict that refractory carbides, like TiC, should condense at higher temperatures than graphite, while SiC condenses at lower temperatures than graphite[1]. TEM observations support these predictions, with refractory carbides often observed as internal subgrains within graphite, whereas SiC is rarely observed inside of graphite [2, 3]. Out of ~1500 Murchison high-density graphite slices examined in the TEM for internal subgrains, only 4 have been found that contain internal SiC grains.

The stellar origin of SiC-containing graphite is uncertain. Most high-density graphites have an AGB origin. However, the graphites with internal SiCs lack clear indicators of an AGB origin, such as s-process enrichments, which are observed in other high-density graphites[3]. TiC and Fe subgrains observed in the SiC-containing graphites have compositions similar to the subgrains found in SN graphites[4]. However, there are no radiogenic isotopes, such as 26Mg, present, which would be a clear indicator of a SN origin. The SiC polytypes are consistent with both mainstream SiC and SiC X-grains and while NanoSIMS analysis of the 12C/13C ratios confirms the presolar origin of these graphites, the 16O/18O ratios are normal within errors, leaving the stellar origin of these grains uncertain.

[1]Lodders K. and Fegley B., Jr. 1995. MAPS. 30:661-678. [2]Bernatowicz T. J.et al. 1996. ApJ. 472:760-782. [3]Croat T. K.et al. 2005. ApJ. 631:976-987. [4]Croat T. K.et al. 2003. GCA. 67:4705-4725.

Preparing for Pallas: Future Hubble Space Telescope Observations

Britney E. SCHMIDT

The material in the asteroid belt presents us with a snapshot of the earliest epoch of the solar system's formation. Telescope observations have revolutionized what we know about the largest asteroids: they are more than simple space rocks, they are evolved, dynamic bodies with important information about solar system origins. The largest asteroids 1 Ceres, 2 Pallas and 4 Vesta grew massive enough to undergo varying degrees of compositional differentiation. are the largest of the asteroids. Ceres and Vesta will be visited by the Dawn spacecraft, but Pallas is presently out of reach. Thus, HST provides the perfect opportunity to study Pallas. Pallas is a B-type asteroid with inclination of 31 0 and estimated shape of 570 x 525 x 482 km. There is spectral evidence that Pallas, like Ceres, has been substantially altered by water. Pallas is at a similar distance from the Sun as Ceres, but is similar in mass to Vesta and so Pallas may provide information about how size and location affect a forming planetessimal's composition and thermal history. In this presentation, I will highlight the current state of knowledge for Pallas, and what we hope to learn from HST observations in September.

Measurements of antipodal velocity in impact experiments of porous sintered targets - A comparison between low and high velocity experiments

Masato SETOH

Porous structure is common in the asteroids and satellites of the outer planets. In order to study the relationship between the structure of small bodies and their thermal and collisional evolution, we prepared porous targets and performed impact experiments. The results of the experiments will be used as a reference for future numerical simulations of collisional process of porous bodies.

In order to produce porous targets, we sintered soda lime glass beads of 50 micron diameter and 2.5g /cm3 nominal density. As a result, sintered glass beads targets had porosity of 10-40% and various compressive strengths. We performed three series of impact experiments. A comparison between the results of these experimental series and a previous one (Love et al.1993) suggested that high velocity impacts need higher specific energy than low velocity impacts for catastrophic disruption when the targets have same compressive strength.

For the purpose of studying the attenuation of the stress wave in the porous targets in both high and low velocity impacts, we measured the antipodal velocity of the targets using high-speed camera images taken at 2.000 -- 64.000 fps. We will present a comparison between the low and the high impact velocities.

Micro-XRD SURVEY OF POSSIBLE CAIs IN THE TAGISH LAKE CHONDRITE (P2 ROM)

Christopher CHARLES

Micro-X-ray diffraction was used to probe the mineralogic content of several mm-sized grey-white grains on the "P2 ROM" specimen of the Tagish Lake carbonaceous chondrite. These grains were clearly visible on a large exposed slab-surface of the interior of P2-ROM (FIGURE 2) and are visually reminiscent of the first known solids in the Solar System: refractory calcium-aluminum-rich inclusions (CAIs). The thawed specimen "P2 ROM" is the largest and most pristine example of the Tagish Lake chondrite, and is slated for permanent display at the Royal Ontario Museum. Such rapid, nondestructive analyses of this highly friable meteorite is essential for applying precise 207Pb/206Pb chronometry to particular refractory lead-bearing phases (and chondrules). Positive identification of CAIs in Tagish is important for resolving precise Pb-Pb dates for this unique specimen.