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A prime question in the formation and early evolution of the Solar system studies is to discern the source(s) of short-lived now extinct nuclides and to determine the ab-initio isotopic composition of our Solar System (ref. 1). The proposed genesis of a short-lived now extinct radionuclide,10Be, by spallation reactions of carbon and oxygen led to the hypothesis of enhanced irradiation in the early Solar system (ref. 2-8). An alternative scenario of production of 10Be (t1/2 =1.386 +- 0.016 million years (ref.9)) by neutrino process in a low mass star (11.8Msun) core collapse supernova has been recently suggested (ref. 10) that can explain the observed abundance of 10Be in the early Solar System. Here, we report well resolved excesses in 7Li/6Li of up to ~21.5 percent in a Type B1 Ca,-Al rich inclusion (CAI) from the Efremovka meteorite that correlate with 9Be/6Li, suggestive of in situ decay of 7Be. The in situ decay of 7Be, with characteristic half-life of 53.12+- 0.07 days (ref. 11) to 7Li, entails multiple episodes of enhanced irradiation in the ESS. The short half-life of 7Be limits its production by interaction of Solar energetic particles with the nebular gas and solids and provides constraints on genealogy and chronology of CAIs. Irradiation of precursor solids/gas of CAIs of Solar composition by a superflare (Lx=10 exp(32) erg/sec) during the terminal phase of class I or II of pre-main sequence stages of the Sun cogently explains the isotopic properties, distinctive petrographic features, and diffusivity constraints in the CAI.

We compute the concentrations of five transition elements (Cr, Fe, Co, Ni and Zn) in supernova presolar grains (Silicon Carbide Type X) from the time they condense till the end of free expansion phase, via condensation and implantation. We consider relative velocities of these elements with respect to grains as they condense and evolve at temperatures $\le$ 2000 K, use zonal nucleosynthesis yields for three core collapse supernovae models - 15 M\textsubscript{\(\odot\)}, 20 M\textsubscript{\(\odot\)} and 25 M\textsubscript{\(\odot\)} and an ion target simulator SDTrimSP to model their implantation onto the grains. Simulations from SDTrimSP show that maximal implantation in the core of the grain is possible, contrary to previous studies. We find that the 15 M\textsubscript{\(\odot\)} model best explains the measured concentrations of SiC X grains obtained from Murchison meteorite. For grains which contained $\ge$ 300 ppm of Fe and Ni, we find implantation fraction to be $\le$ 0.25 for most probable differential zonal velocities in this phase which implies that condensation is dominant than implantation unless the grain did not spend much time in the supernova environment. We show that radioactive corrections and mixing from the innermost zones is vital to explaining the excess Ni (condensed as well as implanted) obtained in laboratory measurements. This mixing also explains the relative abundances of Co and Ni with respect to Fe simultaneously. The model developed can be used to predict concentrations of all other elements in various presolar grains condensed in supernova ejecta and matched against measured concentrations in grains found in meteorites., Comment: 21 pages, 4 figures, 3 tables. Accepted for publication in ApJ. Comments welcome

Ordinary chondrites (OCs) represent the most abundant extraterrestrial materials and also record the widest range of alteration of primary, pristine minerals of early Solar system material available for study. Relatively few investigations, however, address: (1) the role of fluid alteration, and (2) the relationship between thermal metamorphism and metasomatism in OCs, issues that have been extensively studied in many other meteorite groups e.g., CV, CO, CR, and enstatite chondrites. Detailed elemental abundances profiles across individual chondrules, and mineralogical studies of Lewis Hills (LEW) 86018 (L3.1), an unequilibrated ordinary chondrite (UOC) of low petrographic type of 3.1 returned from Antarctica, provide evidence of extensive alteration of primary minerals. Some chondrules have Na(-), K(-), rich rims surrounded by nepheline, albite, and sodalite-like Na(-), Cl(-), Al-rich secondary minerals in the near vicinity within the matrices. Although, limited evidences of low temperature (approximately 250 C) fluid-assisted alteration of primary minerals to phyllosilicates, ferroanolivine, magnetite, and scapolite have been reported in the lowest grades (less than 3.2) Semarkona (LL3.00) and Bishunpur (LL3.10), alkali-rich secondary mineralization has previously only been seen in higher grade greater than 3.4 UOCs. This preliminary result suggests highly localized metamorphism in UOCs and widens the range of alteration in UOCs and complicates classification of petrographic type and extent of thermal metamorphism or metasomatism. The work in progress will document the micro-textures, geochemistry (Ba, Ca, REE), and isotopic composition (oxygen, Al(-)- 26 Mg-26) of mineral phases in chondrules and adjoining objects to help us understand the formation scenario and delineate possible modes of metamorphism in UOCs.

In January 2006, the STARDUST mission successfully returned dust samples from the tail of comet 81P/Wild 2 in two principal collection media, low density silica aerogel and Al foil. While hypervelocity impacts at 6.1 km/s, the encounter velocity of STARDUST, into Al foils are generally highly disruptive for natural, silicate-dominated impactors, previous studies have shown that many craters retain sufficient residue to allow a determination of the elemental and isotopic compositions of the original projectile. We have used the NanoSIMS to perform C, N, and O isotope imaging measurements on four large (59-370 microns diameter) and on 47 small (0.32-1.9 microns diameter) Al foil impact craters as part of the STARDUST Preliminary Examination. Most analyzed residues in and around these craters are isotopically normal (solar) in their C, N, and O isotopic compositions. However, the debris in one large crater shows an average 15N enrichment of approx. 450 %, which is similar to the bulk composition of some isotopically primitive interplanetary dust particles. A 250 nm grain in another large crater has an O-17 enrichment with approx. 2.65 times the solar O-17/O-16 ratio. Such an O isotopic composition is typical for circumstellar oxide or silicate grains from red giant or asymptotic giant branch stars. The discovery of this circumstellar grain clearly establishes that there is authentic stardust in the cometary samples returned by the STARDUST mission. However, the low apparent abundance of circumstellar grains in Wild 2 samples and the preponderance of isotopically normal material indicates that the cometary matter is a diverse assemblage of presolar and solar system materials.

We have explored the feasibility of C-, N-, and O-isotopic measurements by NanoSIMS and of elemental abundance determinations by TOF-SIMS on residues of Allende projectiles that impacted Stardust-type aluminum foils in the laboratory at 6 km/s. These investigations are part of a consortium study aimed at providing the foundation for the characterization of matter associated with micro-craters that were produced during the encounter of the Stardust space probe with comet 81P/Wild 2. Eleven experimental impact craters were studied by NanoSIMS and eighteen by TOF-SIMS. Crater sizes were between 3 and 190 microns. The NanoSIMS measurements have shown that the crater morphology has only a minor effect on spatial resolution and on instrumental mass fractionation. The achievable spatial resolution is always better than 200 nm, and C- and O-isotopic ratios can be measured with a precision of several percent at a scale of several 100 nm, the typical size of presolar grains. This clearly demonstrates that presolar matter, provided it survives the impact into the aluminum foil partly intact, is recognizable even if embedded in material of Solar System origin. TOF-SIMS studies are restricted to materials from the crater rim. The element ratios of the major rockforming elements in the Allende projectiles are well characterized by the TOF-SIMS measurements, indicating that fractionation of those elements during impact can be expected to be negligible. This permits information on the type of impactor material to be obtained. For any more detailed assignments to specific chondrite groups, however, information on the abundances of the light elements, especially C, is crucial.