Refers To

Cyrena A. Goodrich, Richard D. Ash, James A. Van Orman, Kenneth Domanik, William F. McDonough
Metallic phases and siderophile elements in main group ureilites: Implications for ureilite petrogenesis
Geochimica et Cosmochimica Acta, Volume 112, 1 July 2013, Pages 340-373

The publisher regrets the article is incorrectly labelled as “Response” when it is a full length research article. The publisher would like to apologise for any inconvenience caused.

Christoph Loesche¹, Gerhard Wurm¹, Jens Teiser¹, Jon M. Friedrich^2,3, and Addi Bischoff⁴

¹Faculty of Physics, University of Duisburg-Essen, Lotharstr. 1, D-47057 Duisburg, Germany
²Department of Chemistry, Fordham University, Bronx, NY 10458, USA
³Department of Earth and Planetary Sciences, American Museum of Natural History, New York, NY 10024, USA
⁴Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, D-48149 Münster, Germany

Photophoresis is a physical process that transports particles in optically thin parts of protoplanetary disks, especially at the inner edge and at the optical surface. To model the transport and resulting effects in detail, it is necessary to quantify the strength of photophoresis for different particle classes as a fundamental input. Here, we explore photophoresis for a set of chondrules. The composition and surface morphology of these chondrules were measured by X-ray tomography. Based on the three-dimensional models, heat transfer through illuminated chondrules was calculated. The resulting surface temperature map was then used to calculate the photophoretic strength. We found that irregularities in particle shape and variations in composition induce variations in the photophoretic force. These depend on the orientation of a particle with respect to the light source. The variation of the absolute value of the photophoretic force on average over all chondrules is 4.17%. The deviation between the direction of the photophoretic force and illumination is 30 ± 15. The average photophoretic force can be well approximated and calculated analytically assuming a homogeneous sphere with a volume equivalent mean radius and an effective thermal conductivity. We found an analytic expression for the effective thermal conductivity. The expression depends on the two main phases of a chondrule and decreases with the amount of fine-grained devitrified, plagioclase-normative mesostasis up to factor of three. For the chondrule sample studied (Bjurböle chondrite), we found a dependence of the photophoretic force on chondrule size.

Reference
Loesche C, Wurm G, Teiser J, Friedrich JM and Bischoff A (2013) Photophoretic Strength on Chondrules. 1. Modeling. The Astrophysical Journal 778:2.
[doi:10.1088/0004-637X/778/2/101]

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Jiří Borovička¹, Pavel Spurný¹, Peter Brown^2,3, Paul Wiegert^2,3, Pavel Kalenda⁴, David Clark^2,3 and Lukáš Shrbený¹

¹Astronomical Institute, Academy of Sciences of the Czech Republic, CZ-251 65 Ondřejov, Czech Republic
²Department of Physics and Astronomy, University of Western Ontario, London, Ontario N6A 3K7, Canada
³Centre for Planetary Science and Exploration, University of Western Ontario, London, Ontario N6A 5B7, Canada
⁴Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic, V Holešovičkách 41, CZ-18209 Praha 8, Czech Republic

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

Reference
Borovička J, Spurný P, Brown P, Wiegert P, Kalenda P, Clark D and Shrbený L (2013) The trajectory, structure and origin of the Chelyabinsk asteroidal impactor. Nature 503:235–237.
[doi:10.1038/nature12671]

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

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

Reference
Brown et al. (2013) A 500-kiloton airburst over Chelyabinsk and an enhanced hazard from small impactors. Nature 503:238–241.
[doi:10.1038/nature12741]

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M. Minissale¹, E. Congiu¹, G. Manicò², V. Pirronello² and F. Dulieu¹

¹LERMA, UMR8112 du CNRS, de l’Observatoire de Paris et de l’Université de Cergy Pontoise, 5 mail Gay Lussac, 95000 Cergy Pontoise Cedex, France
²Dipartimento di Fisica ed Astronomia, Universitá degli Studi di Catania, via Santa Sofia 64, 95123 Catania, Italy

Context. The formation of carbon dioxide in quiescent regions of molecular clouds has not yet been fully understood, even though CO₂ is one of the most abundant species in interstellar ices.
Aims. CO₂ formation is studied via oxidation of CO molecules on cold surfaces under conditions close to those encountered in quiescent molecular clouds.
Methods. Carbon monoxide and oxygen atoms are codeposited using two differentially pumped beam lines on two different surfaces (amorphous water ice or oxydized graphite) held at given temperatures between 10 and 60 K. The products are probed via mass spectroscopy by using the temperature-programmed desorption technique.
Results. We show that the reaction CO + O can form carbon dioxide in solid phase with an efficiency that depends on the temperature of the surface. The activation barrier for the reaction, based on modelling results, is estimated to be in the range of 780−475 K/k_b. Our model also allows us to distinguish the mechanisms (Eley Rideal or Langmuir-Hinshelwood) at play in different temperature regimes. Our results suggest that competition between CO₂ formation via CO + O and other surface reactions of O is a key factor in the yields of CO₂ obtained experimentally.
Conclusions. CO₂ can be formed by the CO + O reaction on cold surfaces via processes that mimic carbon dioxide formation in the interstellar medium. Astrophysically, the presence of CO₂ in quiescent molecular clouds could be explained by the reaction CO + O occurring on interstellar dust grains.

Reference
Minissale M, Congiu E, Manicò G, Pirronello V and Dulieu F (2013) CO2 formation on interstellar dust grains: a detailed study of the barrier of the CO + O channel. Astronomy & Astrophysics 559:A49.
[doi:10.1051/0004-6361/201321453]
Reproduced with permission © ESO

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Dirk Elbeshausen^1,*, Kai Wünnemann¹, Gareth S. Collins²

¹Museum für Naturkunde, Leibniz-Institute for Research on Evolution and Biodiversity, Berlin, Germany
²Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London, London, UK

Elliptical impact craters are rare among the generally symmetric shape of impact structures on planetary surfaces. Nevertheless, a better understanding of the formation of these craters may significantly contribute to our overall understanding of hypervelocity impact cratering. The existence of elliptical craters raises a number of questions: Why do some impacts result in a circular crater whereas others form elliptical shapes? What conditions promote the formation of elliptical craters? How does the formation of elliptical craters differ from those of circular craters? Is the formation process comparable to those of elliptical craters formed at subsonic speeds? How does crater formation work at the transition from circular to elliptical craters? By conducting more than 800 three-dimensional (3-D) hydrocode simulations, we have investigated these questions in a quantitative manner. We show that the threshold angle for elliptical crater generation depends on cratering efficiency. We have analyzed and quantified the influence of projectile size and material strength (cohesion and coefficient of internal friction) independently from each other. We show that elliptical craters are formed by shock-induced excavation, the same process that forms circular craters and reveal that the transition from circular to elliptical craters is characterized by the dominance of two processes: A directed and momentum-controlled energy transfer in the beginning and a subsequent symmetric, nearly instantaneous energy release.

Reference
Elbeshausen D, Wünnemann K and Collins GS (in press) The transition from circular to elliptical impact craters. Journal of Geophysical Research – Planets
[doi:10.1002/2013JE004477]
Published by arrangement with John Wiley & Sons

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Sherry K. Fieber-Beyer^* and Michael J. Gaffey

Department of Space Studies, University Stop 9008, University of North Dakota, 58202

The 3:1 Kirkwood gap asteroids are a mineralogically diverse set of asteroids located in a region that delivers meteoroids into Earth-crossing orbits. Mineralogical characterizations of asteroids in/near the 3:1 Kirkwood Gap can be used as a tool to “map” conditions and processes in the early solar system. The chronological studies of the meteorite types provide a “clock” for the relative timing of those events and processes. By identifying the source asteroids of particular meteorite types, the “map” and “clock” can be combined to provide a much more sophisticated understanding of the history and evolution of the late solar nebula and the early solar system.
A mineralogical assessment of twelve 3:1 Kirkwood Gap asteroids has been carried out using near-infrared spectral data obtained from 2010-2011 combined with visible spectral data (when available) to cover the spectral interval of 0.4 – 2.5 μm. Eight of these asteroids have surfaces with basaltic-type silicate assemblages, indicating at least partial melting within their parent bodies. Although HED-like mineralogies are present these objects exhibit subdued features indicating the presence of an additional phase (e.g., NiFe metal) or process (e.g., space weathering). Four of these asteroids appear to be ordinary chondrite assemblages. Three of these are plausibly linked to the probable H-chondrite parent body, (6) Hebe.

Reference
Fieber-Beyer SK and Gaffey MJ (in press) Near-infrared Spectroscopy of 3:1 Kirkwood Gap Asteroids II: Probable and Plausible Parent Bodies; Primitive and Differentiated. Icarus
[doi:10.1016/j.icarus.2013.11.001]
Copyright Elsevier

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P. Beck^a,*, A. Garenne^a, E. Quirico^a, L. Bonal^a, G. Montes-Hernandez^b, F. Moynier^c, B. Schmitt^a

^aUJF-Grenoble 1 / CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble, F-38041, France
^bUJF-Grenoble 1 / CNRS-INSU, Institut des Sciences de la Terre (IsTERRE) UMR 5275, Grenoble, F-38041, France
^cDepartment of Earth and Planetary Sciences, Washington University in St Louis

In this work, infrared transmission spectra (2-25 μm range, 5000-400 cm^-1) of 40 carbonacous chondrites were analyzed (21 CMs, 5 CVs, 6 CRs, 3 CKs, 3 C2s and 2 CIs). All these meteorite groups are known to have experienced significant aqueous alteration (except the CKs). These IR measurements provide information about the parent body processes experienced, as well as spectra for comparison with observations of Solar System small bodies and possibly with astronomical observations of accretion and debris disks.
This study reveals that each meteorite group appears to have specific signatures in the measured IR spectral range measured. In the case of the CI and CM groups, results show a variability in the shape of the silicate features that can be related to the evolution of the mineralogy with increasing extent of aqueous alteration extent as described by several authors with other techniques. This evolution of the silicate feature can be seen in the variation in the relative intensities of olivine and phyllosilicate IR features. The variability in the silicate features is correlated with the intensity of an –OH related absorption at 3-μm, which can be used for the classification of the meteorites according to the level of hydration. Interestingly, in the case of CM chondrites, for which the mineralogy is expected to be dominated by phyllosilicates (serpentine mostly), the shape of the silicate absorption ressembles that of an amorphous silicate, with a broad and symmetric 10-μm band, unlike terrestrial phyllosilicates.
The CV and CK groups have IR spectra that are dominated by olivine absorption. From this feature, it is possible to determine average Mg numbers for the olivine. For the CVs, the olivine Mg numbers appear to decrease in the order Kaba-Grosnaja-Vigarano-Mokoia-Allende. This trend is likely related to the long duration of metamorphism experienced by these samples and the chemical re-equilibration between chondritic components. In the case of CK chondrites, the inferred bulk Mg# of olivine is 67 (+/- 1), and no variation is observed between the three studied samples, which is likely related to their high degree of equilibration.
The 6 CR chondrites show the most variability in their IR spectra, from CM-like spectra in the case of the CR1 Grosvenor Moutains (GRO) 95577 to CV-like spectra for Roberts Massif (RBT) 04133 and Graves Nunataks (GRA) 06100 (one of them being most probably misclassified). Spectra of the remaining CRs show mixtures of various silicate component.
Finally, these spectra can be used for comparison with emission spectra of fine-grained asteroid surfaces and dust-rich cometary tails. In the case of Tempel 1, the only group of CC that matches the observed feature around 10-μm region is the CR group. The spectral comparison shows some striking similarities between CRs and Tempel 1 dust. A genetic link between CR2 and comets is not proven, but mineralogical similarities are suggested from the IR spectra.

Reference
Beck P, Garenne A, Quirico E, Bonal L, Montes-Hernandez G, Moynier F and Schmitt B (in press) Transmission infrared spectra (2-25 microns) of carbonaceous chondrites (CI, CM, CV-CK, CR, C2 ungrouped): mineralogy, water, and asteroidal processes. Icarus
[doi:10.1016/j.icarus.2013.10.019]
Copyright Elsevier

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Evelyn Füri^*, Etienne Deloule, Andrey Gurenko and Bernard Marty

Centre de Recherches Pétrographiques et Géochimiques, 15 rue Notre-Dame des Pauvres, BP20, 54501 Vandoeuvre-lès-Nancy Cedex, France

In order to assess the proportion of solar, cosmogenic, and indigenous water (hydrogen) trapped in individual Ti-rich lunar volcanic glasses (LVGs) from the 74002 core obtained during the Apollo 17 mission, we coupled ion microprobe measurements of water abundances and D/H ratios with CO₂ laser extraction-static mass spectrometry analyses of noble gases (He, Ne, Ar). The large (∼300-400 μm in diameter) LVGs studied here contain a small amount of solar wind (SW) volatiles implanted at the grain surfaces, as indicated by the small concentrations of solar helium and neon that represent ⩽5% of the respective total noble gas abundances. The large proportion of volume-correlated cosmogenic gases reflects an exposure duration of ∼28 Ma, on average, of the glasses at the lunar surface. Hydrogen abundances determined in the grain interiors of glassy and partially-crystalline LVGs are equivalent to between 6.5 and 54.3 ppm H₂O. Based on the noble gas exposure ages, the correction of the measured hydrogen isotope composition for in-situ production of cosmogenic deuterium by spallation reactions varies between -5 to -254 ‰ for the different grains. Corrected δD values range from +38 ‰ to +809 ‰ in the LVGs and are anti-correlated with the water content, consistent with extensive hydrogen isotope fractionation during kinetic H₂ loss from a lunar melt with an inferred initial isotope signature of the order of -100 ‰ and a water content of 100-300 ppm. The detection of water in these primitive lunar melts confirms the presence of a non-anhydrous mantle reservoir within the Moon. Furthermore, our results reveal that the hydrogen isotope composition of water in the melt source of the 74002 LVGs is similar to that of carbonaceous chondrites. These observations indicate that the contribution of deuterium-enriched cometary water to the Earth-Moon system is negligible.

Reference
Füri E, Deloule E, Gurenko A and Marty B (in press) New evidence for chondritic lunar water from combined D/H and noble gas analyses of single Apollo 17 volcanic glasses. Icarus
[doi:10.1016/j.icarus.2013.10.029]
Copyright Elsevier

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M. de Val-Borro^1,2, M. Küppers³, P. Hartogh¹, L. Rezac¹, N. Biver⁴, D. Bockelée-Morvan⁴, J. Crovisier⁴, C. Jarchow¹ and G. L. Villanueva^5,6

¹Max Planck Institute for solar system Research, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
²Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
³Rosetta Science Operations Centre, European Space Astronomy Centre, European Space Agency, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁴LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France
⁵solar system Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁶Department of Physics, Catholic University of America, Washington, DC 20064, USA

Context. The chemical composition of comets can be inferred using spectroscopic observations in submillimeter and radio wavelengths.
Aims. We aim to compare the production rates ratio of several volatiles in two comets, C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR), which are generally regarded as dynamically new and likely to originate in the Oort cloud. This type of comets is considered to be composed of primitive material that has not undergone considerable thermal processing.
Methods. The line emission in the coma was measured in the comets, C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR), that were observed on five consecutive nights, 7–11 May 2004, at heliocentric distances of 1.0 and 0.7 AU, respectively, by means of high-resolution spectroscopy using the 10-m Submillimeter Telescope at the Arizona Radio Observatory. Both objects became very bright and reached naked-eye visibility during their perihelion passage in the spring of 2004.
Results. We present a search for six parent- and product-volatile species (HCN, H₂CO, CO, CS, CH₃OH, and HNC) in both comets. Multiline observations of the CH₃OH J = 5−4 series allow us to estimate the rotational temperature using the rotation diagram technique. We derive rotational temperatures of 54(9) K for C/2001 Q4 (NEAT) and 119(34) K for C/2002 T7 (LINEAR). The gas production rates are computed using the level distribution obtained with a spherically symmetric molecular excitation code that includes collisions between neutrals and electrons. The effects of radiative pumping of the fundamental vibrational levels by infrared photons from the Sun are considered for the case of HCN. We find an HCN production rate of 2.96(5) × 1026 molec.s^-1 for comet C/2001 Q4 (NEAT), corresponding to a mixing ratio with respect to H₂O of 1.12(2) × 10^-3. The mean HCN production rate during the observing period is 4.54(10) × 10²⁶ molec.s^-1 for comet C/2002 T7 (LINEAR), which gives a mixing ratio of 1.51(3) × 10³. Relative abundances of CO, CH₃OH, H₂CO, CS, and HNC with respect to HCN are 3.05(83) × 10¹, 1.50(25) × 10¹, 1.16(27), 7.02(30) × 10^-1, and 5.75(73) × 10^-2 in comet C/2001 Q4 (NEAT) and < 4.12 × 10¹, 4.07(44) × 10¹, 4.72(73), 1.32(6), and 1.09(8) × 10^-1 in comet C/2002 T7 (LINEAR).
Conclusions. With systematically lower mixing ratios in comet C/2001 Q4 (NEAT), production rate ratios of the observed species with respect to H₂O lie within the typical ranges of dynamically new comets in both objects. We find a relatively low abundance of CO in C/2001 Q4 (NEAT) compared to the observed range in other comets based on millimeter/submillimeter observations, and a significant upper limit on the CO production in C/2002 T7 (LINEAR) is derived. Depletion of CO suggests partial evaporation from the surface layers during previous visits to the outer solar system and agrees with previous measurements of dynamically new comets. Rotational temperatures derived from CH₃OH rotational diagrams in both C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR) are roughly consistent with observations of other comets at similar distances from the Sun.

Reference
de Val-Borro M, Küppers M, Hartogh P, Rezac L, Biver N, Bockelée-Morvan D, Crovisier J, Jarchow C and Villanueva GL (in press) A survey of volatile species in Oort cloud comets C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR) at millimeter wavelengths. Astronomy & Astrophysics 559:A48.
[doi:10.1051/0004-6361/201322284]
Reproduced with permission © ESO

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