D. S. Burnett

Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA

The Genesis Discovery mission returned solar matter in the form of the solar wind with the goal of obtaining precise solar isotopic abundances (for the first time) and greatly improved elemental abundances. Measurements of the light noble gases in regime samples demonstrate that isotopes are fractionated in the solar wind relative to the solar photosphere. Theory is required for correction. Measurement of the solar wind O and N isotopes shows that these are very different from any inner solar system materials. The solar O isotopic composition is consistent with photochemical self-shielding. For unknown reasons, the solar N isotopic composition is much lighter than essentially all other known solar system materials, except the atmosphere of Jupiter. Ne depth profiling on Genesis materials has demonstrated that Ne isotopic variations in lunar samples are due to isotopic fractionation during implantation without appealing to higher energy solar particles. Genesis provides a precise measurement of the isotopic differences of Ar between the solar wind and the terrestrial atmosphere. The Genesis isotopic compositions of Kr and Xe agree with data from lunar ilmenite separates, showing that lunar processes have not affected the ilmenite data and that solar wind composition has not changed on 100 Ma time scales. Relative to Genesis solar wind, ArKrXe in Q (the chondrite noble gas carrier) and the terrestrial atmosphere show relatively large light isotope depletions.

Reference
Burnett DS (in press) The Genesis solar wind sample return mission: Past, present, and future. Meteoritics & Planetary Science
[doi:10.1111/maps.12241]
Published by arrangement with John Wiley & Sons

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Yoshihiro Furukawa Taro Samejima, Hiromoto Nakazawa and Takeshi Kakegawa

Department of Earth Science, Graduate School of Science, Tohoku University

Late heavy bombardment (LHB) of extraterrestrial objects supplied carbon with metals to the prebiotic Earth. The early oceans were the major target of these impacts, followed by interactions among the atmosphere, oceanic water, and meteorite constituent materials under high-temperature and high-pressure conditions. Post-impact reactions of these hypervelocity impacts have the potential to produce reduced volatiles and organic compounds, including amino acids. Therefore, understanding the reactions in post-impact plumes is of great importance for the investigation of prebiotic organic compounds. The composition of post-impact plumes has been investigated with thermochemical calculations. However, experimental evidence is still needed to understand the reactions in dynamic systems of post-impact plumes. The present study investigates the effects of reaction temperature and availability of water on products from iron, nickel, graphite, nitrogen, and water in a dynamic gas flow system to investigate reactions in post-impact plumes. Results of this study indicate the formation of CO, H₂, NH₃, and HCN by hypervelocity oceanic impacts of iron-rich extraterrestrial objects. The formation of methane was limited in the present experiments, suggesting that the quenching rate is an influential factor for methane formation in post-impact plumes. Availability of water vapor in the plume was also an influential factor for the formation of reduced volatiles that controlled the CO formation rate from graphite. These results provide experimental evidence for the formation of reduced volatiles in post-impact plumes, which influenced the formation of pre-biotic organic compounds.

Reference
Furukawa Y, Samejima T, Nakazawa H and Kakegawa T (in press) Experimental investigation of reduced volatile formation by high-temperature interactions among meteorite constituent materials, water, and nitrogen. Icarus
[doi:10.1016/j.icarus.2013.11.033]
Copyright Elsevier

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M. Fouchard^a, H. Rickman^b,c, Ch. Froeschlé^d, G.B. Valsecchi^e,f

^aLAL-IMCCE, Université de Lille 1, 1 Impasse de l’Observatoire, F-59000 Lille, France
^bPAS Space Research Center, Bartycka 18A, PL-00-716, Warszawa, Poland
^cDept. of Physics & Astronomy, Uppsala Univ., Box 516, SE-75120 Uppsala, Sweden
^dObservatoire de la Côte d’Azur, UMR Lagrange 7293, Bv. de l’Observatoire, B.P. 4229, F-06304 Nice cedex 4, France
^eIAPS, INAF, via Fosso del Cavaliere 100, I-00133 Roma, Italy
^fIFAC-CNR, Via Madonna del Piano 10, I-50019 Sesto Fiorentino (FI), Italy

We present Monte Carlo simulations of the dynamical history of the Oort cloud, where in addition to the main external perturbers (Galactic tides and stellar encounters) we include, as done in a companion paper (Fouchard et al. 2013b), the planetary perturbations experienced each time the comets penetrate to within 50 AU of the Sun. Each simulation involves an initial sample of four million comets and extends over a maximum of 5 Gyr. For better understanding of the outcomes, we supplement the full dynamical model by others, where one or more of the effects are left out. We concentrate on the production of observable comets, reaching for the first time a perihelion within 5 AU of the Sun. We distinguish between four categories, depending on whether the comet jumps across, or creeps through, the Jupiter-Saturn barrier (perihelion distances between 5 and 15 AU), and whether the orbit leading to the observable perihelion is preceded by a major planetary perturbation or not. For reasons explained in the paper, we call the strongly perturbed comets “Kaib-Quinn comets”.
We thus derive a synthetic picture of the Oort spike, from which we draw two main conclusions regarding the full dynamical model. One is that 2/3 of the observable comets are injected with the aid of a planetary perturbation at the previous perihelion passage, and about half of the observable comets are of the Kaib-Quinn type. The other is that the creepers dominate over the jumpers. Due to this fact, the spike peaks at only 31 000AU, and the majority of new comets have semi-major axes less than this value. The creepers show a clear preference for retrograde orbits as a consequence of the need to avoid untimely, planetary ejection before becoming observable. Thus, the new comets should have a 60/40 preference for retrograde against prograde orbits in apparent conflict with observations. However, both these and other results depend on our model assumptions regarding the initial structure of the Oort cloud, which is isotropic in shape and has a relatively steep energy distribution. We also find that they depend on the details of the past history of external perturbations including GMC encounters, and we provide special discussions of those issues.

Reference
Fouchard M, Rickman H, Froeschlé Ch and Valsecchi GB (in press) Planetary perturbations for Oort cloud comets: II. Implications for the origin of observable comets. Icarus
[doi:10.1016/j.icarus.2013.11.032]
Copyright Elsevier

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P. J. Wozniakiewicz^1,2, J. P. Bradley³, H. A. Ishii³, M. C. Price² and D. E. Brownlee⁴

¹Earth Sciences Department, Mineral and Planetary Science Division, Natural History Museum, Cromwell Road, London SW7 5BD, UK
²School of Physical Sciences, University of Kent, Canterbury, Kent CT2 7NH, UK
³Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
⁴Department of Astronomy, University of Washington, Seattle, WA 98195, USA

Despite their micrometer-scale dimensions and nanogram masses, chondritic porous interplanetary dust particles (CP IDPs) are an important class of extraterrestrial material since their properties are consistent with a cometary origin and they show no evidence of significant post-accretional parent body alteration. Consequently, they can provide information about grain accretion in the comet-forming region of the outer solar nebula. We have previously reported our comparative study of the sizes and size distributions of crystalline silicate and sulfide grains in CP IDPs, in which we found these components exhibit a size–density relationship consistent with having been sorted together prior to accretion. Here we extend our data set and include GEMS (glass with embedded metal and sulfide), the most abundant amorphous silicate phase observed in CP IDPs. We find that while the silicate and sulfide sorting trend previously observed is maintained, the GEMS size data do not exhibit any clear relationship to these crystalline components. Therefore, GEMS do not appear to have been sorted with the silicate and sulfide crystals. The disparate sorting trends observed in GEMS and the crystalline grains in CP IDPs present an interesting challenge for modeling early transport and accretion processes. They may indicate that several sorting mechanisms operated on these CP IDP components, or alternatively, they may simply be a reflection of different source environments.

Reference
Wozniakiewicz PJ, Bradley JP, Ishii HA, Price MC and Brownlee DE (2013) Pre-Accretional Sorting of Grains in the Outer Solar Nebula. The Astrophysical Journal 779:164.
[doi:10.1088/0004-637X/779/2/164]

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Dana E. Anderson¹, Edwin A. Bergin¹, Sébastien Maret² and Valentine Wakelam^3,4

¹Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042, USA
²UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble, F-38041, France
³Univ. Bordeaux, LAB, UMR 5804, F-33270, Floirac, France
⁴CNRS, LAB, UMR 5804, F-33270, Floirac, France

We present observations of fine-structure line emission of atomic sulfur, iron, and rotational lines of molecular hydrogen in shocks associated with several Class 0 protostars obtained with the Infrared Spectrograph of the Spitzer Space Telescope. We use these observations to investigate the “missing sulfur problem,” that significantly less sulfur is found in dense regions of the interstellar medium (ISM) than in diffuse regions. For sources where the sulfur fine-structure line emission is co-spatial with the detected molecular hydrogen emission and in the presence of weak iron emission, we derive sulfur and H2 column densities for the associated molecule-dominated C-shocks. We find the S i abundance to be 5%–10% of the cosmic sulfur abundance, indicating that atomic sulfur is a major reservoir of sulfur in shocked gas. This result suggests that in the quiescent dense ISM sulfur is present in some form that is released from grains as atoms, perhaps via sputtering, within the shock.

Reference
Anderson DE, Bergin EA, Maret S and Wakelam V (2013) New Constraints on the Sulfur Reservoir in the Dense Interstellar Medium Provided by Spitzer Observations of S I in Shocked Gas. The Astrophysical Journal 779:141.
[doi:10.1088/0004-637X/779/2/141]

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Zita Martins¹, Mark C. Price², Nir Goldman³, Mark A. Sephton¹ and Mark J. Burchell²

¹Department of Earth Science and Engineering, Imperial College London, SW7 2AZ, UK
²School of Physical Sciences, University of Kent, Canterbury CT2 7NH, UK
³Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, USA

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

Reference
Martins Z, Price MC, Goldman N, Sephton MA and Burchell MJ (2013) Shock synthesis of amino acids from impacting cometary and icy planet surface analogues. Nature Geoscience 6:1045–1049.
[doi:10.1038/ngeo1930]

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

Physical Sciences Department, Kingsborough Community College of the City University of New York, 2001 Oriental Boulevard, Brooklyn, New York 11235, USA

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

Reference
Howard et al. (2013) Shock synthesis of amino acids from impacting cometary and icy planet surface analogues. Nature Geoscience 6:1018–1022.
[doi:10.1038/ngeo1996]

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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

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

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

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

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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