Corentin Le Guillou^a, Sylvain Bernard^b, Adrian J. Brearley^a, Laurent Remusat^b

^aDepartment of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA
^bLaboratoire de Minéralogie et Cosmochimie du Muséum, UMR CNRS 7202, MNHN, CP 52, 57 rue Cuvier, 75231 Paris Cedex 05, France

Chondrites accreted the oldest solid materials in the solar system including dust processed in the protoplanetary disk and diverse organic compounds. After accretion, asteroidal alteration may have impacted organic particles in various ways. To constrain these processes, we conducted a comprehensive study of organics disseminated within the matrices of the three carbonaceous chondrite falls, Renazzo (CR2), Murchison (CM2) and Orgueil (CI1). By combining synchrotron-based STXM and TEM analyses on FIB sections of samples previously characterized by NanoSIMS, we investigated the influence of aqueous alteration on the morphology, isotopic signature, molecular structure, spatial distribution, and mineralogical environment of this organic matter within the matrices. Two different populations of materials are distinguishable: sub-micrometric individual grains, likely dominated by insoluble compounds and diffuse organic matter, finely interspersed within phyllosilicates and/or (amorphous) nanocarbonates at the nanometer scale. We suggest that this latter component, which is depleted in aromatics and enriched in carboxylic functional groups, may be dominated by soluble compounds. Organic matter in Renazzo (CR) mainly consists of chemically-homogeneous individual grains surrounded by amorphous and nanocrystalline phyllosilicates. Evidence of connectivity between organic grains and fractures indicates that redistribution has occurred: some areas containing diffuse organic matter can be observed. This diffuse organic component is more abundant in Murchison (CM) and Orgueil (CI). This is interpreted as resulting from fluid transport at the micrometer scale and encapsulation within recrystallized alteration phases. In contrast to Renazzo, organic grains in Murchison and Orgueil display strong chemical heterogeneities, likely related to chemical evolution during aqueous alteration. The observations suggest that the altering fluid was a brine with elevated concentrations of both organic and inorganic soluble components. Ultimately, when water was consumed by aqueous alteration reactions or lost from the system, soluble organic compounds accumulated in the immediate vicinity of the precipitated carbonates and phosphates. Additionally, the nanometer scale organic/phyllosilicate relationships provide a petrological environment where some of the initially accreted organic matter could have been modified through clay-mediated reactions.

Reference
Le Guillou C, Bernard S, Brearley AJ and Remusat L (in press) Evolution of organic matter in Orgueil, Murchison and Renazzo during parent body aqueous alteration: in-situ investigations. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2013.11.020]
Copyright Elsevier

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E. Ammannito et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Istituto di Astrofisica e Planetologia Spaziali, INAF, 00133 Rome, Italy

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Reference
Ammannito et al. (2013) Olivine in an unexpected location on Vesta’s surface. Nature 504:122–125.
[doi:10.1038/nature12665]

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Linda T. Elkins-Tanton

Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington, D.C. 20015, USA

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Reference
Elkins-Tanton LT (2013) Planetary science: Occam’s origin of the Moon. Nature Geoscience 6:996–998.
[doi:10.1038/ngeo2026]

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Tim Elliott¹ and Sarah T. Stewart²

¹School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK.
²Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.

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Reference
Elliott T and Stewart ST (2013) Planetary science: Shadows cast on Moon’s origin. Nature 504:90–91.
[doi:10.1038/504090a]

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Robin Canup

Planetary Science Directorate of Southwest Research Institute, Boulder, Colorado.

We still seek a copyright agreement with Nature to display abstracts of their cosmochemistry related publications.

Reference
Canup R (2013) Planetary science: Lunar conspiracies. Nature 504:27–29.
[doi:10.1038/504027a]

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James J. Wray¹, Sarah T. Hansen¹, Josef Dufek¹, Gregg A. Swayze², Scott L. Murchie³, Frank P. Seelos³, John R. Skok⁴, Rossman P. Irwin III⁵ and Mark S. Ghiorso⁶

¹School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
²US Geological Survey, Denver, Colorado 80225, USA
³Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland 20723, USA
⁴Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA
⁵Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington DC 20013, USA
⁶OFM Research, Seattle, Washington 98115, USA

We still seek a copyright agreement with Nature to display abstracts of their cosmochemistry related publications.

Reference
Wray JJ, Hansen ST, Dufek J, Swayze GA, Murchie SL, Seelos FP, Skok JR, Irwin III RP and Ghiorso MS (2013) Prolonged magmatic activity on Mars inferred from the detection of felsic rocks. Nature Geoscience 6:1013–1017.
[doi:10.1038/ngeo1994]

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J. Carter¹ & F. Poulet²

¹European Southern Observatory, Vitacura 763 0355, Santiago, Chile
²Institut d’Astrophysique Spatiale, Université Paris-Sud, Orsay 91405, France

We still seek a copyright agreement with Nature to display abstracts of their cosmochemistry related publications.

Reference
Carter J and Poulet F (2013) Ancient plutonic processes on Mars inferred from the detection of possible anorthositic terrain. Nature Geoscience 6:1008–1012.
[doi:10.1038/ngeo1995]

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Briony Horgan

School of Earth and Space Exploration, Arizona State University, PO Box 876305, Tempe, Arizona, 85287, USA

We still seek a copyright agreement with Nature to display abstracts of their cosmochemistry related publications.

Reference
Horgan B (2013) Planetary science: Evolved magma on Mars. Nature Geoscience 6:991–992.
[doi:10.1038/ngeo2010]

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L. Neslušan¹, M. Hajduková jr.² and M. Jakubík¹

¹Astronomical Institute, Slovak Academy of Science, 05960 Tatranská Lomnica, Slovakia
²Astronomical Institute, Slovak Academy of Science, Dúbravská cesta 9, 84504 Bratislava, Slovakia

Aims. We studied the structure of the meteoroid particle complexes released from asteroid 196 256 (2003 EH1) to reveal the relationship to the meteor showers observed in Earth’s atmosphere that belong to this complex as well. In addition, we studied the relationship between the asteroid and comet 96P/Machholz, which is situated in the same orbital phase space.
Methods. For nine perihelion passages of the parent asteroid in the past, we modeled the associated theoretical streams and followed their dynamical evolution until the present. Subsequently, we analyzed the orbital characteristics of the modeled streams, especially of the parts that approach Earth’s orbit.
Results. We confirm the filamentary structure of the complex, which is qualitatively identical to the complex of 96P. Six well-established and two minor filaments approach the orbit of the Earth, producing four well-known meteor showers, daytime Arietids, Southern δ-Aquarids, Quadrantids, and Northern δ-Aquarids. The filaments corresponding to the Arietids and δ-Aquarids S and N constitute the ecliptical component, and those corresponding to the Quadrantids and their southern counterpart constitute the toroidal component of the complex.

Reference
Neslušan L, Hajduková jr. M and Jakubík M (2013) Meteor-shower complex of asteroid 2003 EH1 compared with that of comet 96P/Machholz. Astronomy & Astrophysics 560:A47.
[doi:10.1051/0004-6361/201322228]
Reproduced with permission © ESO

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