E. Dobrică and A. J. Brearley
Department of Earth and Planetary Sciences, University of New Mexico, MSC03-2040, Albuquerque, New Mexico, USA

The diversity of silicate, glassy spherules analogous to chondrules, called microchondrules, and the implications for their presence in unequilibrated ordinary chondrites (UOCs) were investigated using different electron microscope techniques. Our observations show that the abundance of microchondrules in UOCs is much larger than the values proposed by previous studies. We identified two different types of microchondrules, porous and nonporous, embedded within fine-grained matrices and type I chondrule rims. The porous microchondrules are characterized by distinctive textures and chemical compositions that have not been recognized previously. Additionally, we show detailed textures and chemical compositions of protuberances of silicate materials, connected to the chondrules and ending with microchondrules. We suggest that microchondrules and protuberances formed from materials splattered from the chondrules during stochastic collisions when they were still either completely or partially molten. The occurrence and distinct morphologies of microchondrules and protuberances suggest that rather than just a passive flash melting of chondrules, an additional event perturbed the molten chondrules before they underwent cooling. The bulk chemical compositions suggest that (1) nonporous microchondrules and protuberances were formed by splattering of materials that are compositionally similar to the bulk silicate composition of type I chondrules, and (2) the porous microchondrules could represent the splattered melt products of a less evolved, fine-grained dust composition. The preservation of protuberances and microchondrules in the rims suggests that the cooling and accretion rates were exceptionally fast and that they represent the last objects that were formed before the accretion of the parent bodies of OCs.

Reference
Dobrică E and Brearley AJ (2016) Microchondrules in two unequilibrated ordinary chondrites: Evidence for formation by splattering from chondrules during stochastic collisions in the solar nebula. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12633]
Published by arrangement with John Wiley & Sons

N. Meftah^1,2,3, S. Mostefaoui⁴, A. Jambon², E. H. Guedda³ and S. Pont^4
1Faculté des Mathématiques et des Sciences de la Matière, Université Kasdi Merbah, Ouargla, Algeria
²Sorbonne Universités ISTEP UMR 7193, UPMC, Paris Cedex 05, France
³Laboratoire LEVRES et Faculté des Sciences et technologie, Université d’El-Oued, El-Oued, Algeria
⁴IMPMC, Muséum National d’Histoire Naturelle, Paris, France

We report in situ NanoSIMS siderophile minor and trace element abundances in individual Fe-Ni metal grains in the unequilibrated chondrite Krymka (LL3.2). Associated kamacite and taenite of 10 metal grains in four chondrules and one matrix metal were analyzed for elemental concentrations of Fe, Ni, Co, Cu, Rh, Ir, and Pt. The results show large elemental variations among the metal grains. However, complementary and correlative variations exist between adjacent kamacite-taenite. This is consistent with the unequilibrated character of the chondrite and corroborates an attainment of chemical equilibrium between the metal phases. The calculated equilibrium temperature is 446 ± 9 °C. This is concordant with the range given by Kimura et al. (2008) for the Krymka postaccretion thermal metamorphism. Based on Ni diffusivity in taenite, a slow cooling rate is estimated of the Krymka parent body that does not exceed ~1K Myr⁻¹, which is consistent with cooling rates inferred by other workers for unequilibrated ordinary chondrites. Elemental ionic radii might have played a role in controlling elemental partitioning between kamacite and taenite. The bulk compositions of the Krymka metal grains have nonsolar (mostly subsolar) element/Ni ratios suggesting the Fe-Ni grains could have formed from distinct precursors of nonsolar compositions or had their compositions modified subsequent to chondrule formation events.

Reference
Meftah N, Mostefaoui S, Jambon A, Guedda EH and Pont S (2016) Minor and trace element concentrations in adjacent kamacite and taenite in the Krymka chondrite. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12617]
Published by arrangement with John Wiley & Sons

J. W. Aerts¹, A. Elsaesser², W. F. M. Röling¹ and P. Ehrenfreund^2,3
1Molecular Cell Physiology, Faculty of Earth and Life Sciences, VU University Amsterdam, Amsterdam, the Netherlands
²Leiden Observatory, Leiden University, Leiden, the Netherlands
³Space Policy Institute, George Washington University, Washington, District of Columbia, USA

The Orgueil meteorite has become one of the most well-studied carbonaceous meteorites, after it fell in France 150 yr ago. Extraterrestrial organic compounds such as amino acids and nucleobases in the parts per billion ranges were identified in Orgueil samples with supporting isotopic analyses. However, speculations of terrestrial contamination such as organic inclusions in the form of microbes and seeds accompanied the analyses of the Orgueil meteorite ever since its fall. By using molecular analysis, we performed DNA extractions and spiking experiments combined with 16S and 18S rRNA gene targeted PCR amplification to quantify the level of terrestrial biocontamination. Our results indicate that terrestrial contamination with DNA was insignificant in the investigated meteorite fraction. We also remeasured and confirmed concentrations of amino acids found in previous studies and conclude that their rather high concentrations and distribution cannot be explained by terrestrial contamination with microorganisms alone. These results represent the first analysis using DNA-directed tools in the analysis of the Orgueil meteorite to determine trace levels of biomarkers.

Reference
Aerts JW, Elsaesser A, Röling WFM and Ehrenfreund P (2016) A contamination assessment of the CI carbonaceous meteorite Orgueil using a DNA-directed approach. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12629]
Published by arrangement with John Wiley & Sons