¹Gattacceca, J., ¹P. Rochette, ²R. B. Scorzelli, ²P. Munayco, ³C. Agee, ¹Y. Quesnel, ¹C. Cournède, ⁴J. Geissman

¹CNRS/Aix Marseille Université, CEREGE UM34, Aix-en-Provence, France
²CBPF, Rio de Janeiro, Rio de Janeiro, Brazil
³Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
⁴Department of Geosciences, University of Texas at Dallas, Richardson, Texas, USA

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Reference
Gattacceca J, Rochette P, Scorzelli RB, Munayco P, Agee A, Quesnel Y, Cournède C, Geissman J (2014), Martian meteorites and Martian magnetic anomalies: A new perspective from NWA 7034, Geophysical Research Letters, 41.

Link to Article [DOI: 10.1002/2014GL060464]

¹Ahrens, L. H.

¹Department of Geology and Geophysics, Massachusetts Institute of Technology, USA

Frequency distribution plots of K, Rb, Sc, V, Co, Ga, Cr, and Zr in Ontario diabase, Sc, V, Ga, Cr, La, and Zr in Canadian granite, K, Rb, and Cs in New England granite and F and Mo in granite from various localities are regular, but assume decided positive skewness when dispersion is large, hence, distribution of concentration is not normal. All distributions become normal, or nearly so, provided the variate (concentration of an element) is transformed to log concentration: this leads to a statement of a fundamental (lognormal) law concerning the nature of the distribution of the concentration of an element in specific igneous rocks.
A subsidiary law concerning the relationship between averages and most prevalent concentrations follows as a direct consequence of the fundamental law.
Dispersions of different elements can be compared and predictions may be made on the basis of the lognormal law. A comparison of the dispersions of elements in igneous rocks and chondrites emphasizes the strikingly high uniformity of abundance of many elements in these meteorites. A given element may show a totally different magnitude of dispersion in different igneous rocks, for example, dispersion of scandium is small in diabase and extreme in granite.
“The linear scale, since it was first cut on the wall of an Egyptian temple, has come to be accepted by man almost as if it were the unique scale with which Nature builds and works. Whereas, it is nothing of the sort”—(Bagnold, 1941)

Reference
Ahrens LH (1954) The lognormal distribution of the elements (A fundamental law of geochemistry and its subsidiary). Geochimica et Cosmochimica Acta 5,49-73.
Link to Article [DOI: 10.1016/0016-7037(54)90040-X]

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^1,2,3 Robert A. Wittenmyer et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹School of Physics, UNSW Australia, Sydney, NSW 2052, Australia
²Australian Centre for Astrobiology, UNSW Australia, Sydney, NSW 2052, Australia
³Computational Engineering and Science Research Centre, University of Southern Queensland, Toowoomba, Queensland 4350, Australia

We report the detection of GJ 832c, a super-Earth orbiting near the inner edge of the habitable zone of GJ 832, an M dwarf previously known to host a Jupiter analog in a nearly circular 9.4 yr orbit. The combination of precise radial-velocity measurements from three telescopes reveals the presence of a planet with a period of 35.68 ± 0.03 days and minimum mass (m sin i) of 5.4 ± 1.0 Earth masses. GJ 832c moves on a low-eccentricity orbit (e = 0.18 ± 0.13) toward the inner edge of the habitable zone. However, given the large mass of the planet, it seems likely that it would possess a massive atmosphere, which may well render the planet inhospitable. Indeed, it is perhaps more likely that GJ 832c is a “super-Venus,” featuring significant greenhouse forcing. With an outer giant planet and an interior, potentially rocky planet, the GJ 832 planetary system can be thought of as a miniature version of our own solar system.

Reference
Wittenmyer RA et al. (2014) GJ 832c: A Super-Earth in the Habitable Zone. The Astrophysical Journal 791, 114.
Link to Article [doi:10.1088/0004-637X/791/2/114]

¹Takashi Mikouchi et al. (>10)*
¹Department of Earth and Planetary Science, Graduate School of Science, The
University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

*Find the extensive, full author and affiliation list on the publishers website.

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Reference
Mikouchi T et al. (2014) Mineralogy and crystallography of some Itokawa particles returned by the Hayabusa asteroidal sample return Mission.
Earth, Planets and Space , 66:82
Link to Article [doi:10.1186/1880-5981-66-82]

^1,2 Sebastian M. Stammler, ²Cornelis P. Dullemond
¹ Heidelberg University, Center for Astronomy, Institute of Theoretical Astrophysics, Albert-Ueberle-Straße 2, 69120 Heidelberg, Germany
² Member of the International Max Planck Research School for Astronomy and Cosmic Physics at the Heidelberg University

In recent years many models of chondrule formation have been proposed. One of those models is the processing of dust in shock waves in protoplanetary disks. In this model, the dust and the chondrule precursors are overrun by shock waves, which heat them up by frictional heating and thermal exchange with the gas.
In this paper we reanalyze the nebular shock model of chondrule formation and focus on the downstream boundary condition. We show that for large-scale plane-parallel chondrule-melting shocks the postshock equilibrium temperature is too high to avoid volatile loss. Even if we include radiative cooling in lateral directions out of the disk plane into our model (thereby breaking strict plane-parallel geometry) we find that for a realistic vertical extent of the solar nebula disk the temperature decline is not fast enough. On the other hand, if we assume that the shock is entirely optically thin so that particles can radiate freely, the cooling rates are too high to produce the observed chondrules textures. Global nebular shocks are therefore problematic as the primary sources of chondrules.

Reference
Stammler SM, Dullemond CP (2014) A critical analysis of shock models for chondrule Formation. Icarus(in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.07.024]

Copyright Elsevier

^1,2Kun Wang, ^1,3,4Paul S. Savage, ^1,4Frédéric Moynier

¹ Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St Louis, One Brookings Drive, St. Louis, MO 63130, USA
² Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, USA
³ Department of Earth Sciences, Durham University, Science Labs, Durham DH1 3LE, United Kingdom
⁴ Institut de Physique du Globe de Paris, Institut Universitaire de France, Université Paris Diderot, Sorbonne Paris Cité, 1 rue Jussieu, 75238, Paris Cedex 05, France

Despite their unusual chemical composition, it is often proposed that the enstatite chondrites represent a significant component of Earth’s building materials, based on their terrestrial similarity for numerous isotope systems. In order to investigate a possible genetic relationship between the Fe isotope composition of enstatite chondrites and the Earth, we have analyzed 22 samples from different subgroups of the enstatite meteorites, including EH and EL chondrites, aubrites (main group and Shallowater) and the Happy Canyon impact melt. We have also analyzed the Fe isotopic compositions of separated (magnetic and non-magnetic) phases from both enstatite chondrites and achondrites.

On average, EH3-5 chondrites (δ56Fe = 0.003 ±0.042‰; 2 standard deviation; n=9; including previous literature data) as well as EL3 chondrites (δ56Fe = 0.030 ±0.038‰; 2SD; n=2) have identical and homogeneous Fe isotopic compositions, indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite. In contrast, EL6 chondrites display a larger range of isotopic compositions (−0.180‰ < δ56Fe < 0.181‰; n=11), a result of mixing between isotopically distinct mineral phases (metal, sulfide and silicate). The large Fe isotopic heterogeneity of EL6 is best explained by chemical/mineralogical fragmentation and brecciation during the complex impact history of the EL parent body.

Enstatite achondrites (aubrites) also exhibit a relatively large range of Fe isotope compositions: all main group aubrites are enriched in the light Fe isotopes (δ56Fe = −0.170 ±0.189‰; 2SD; n=6), while Shallowater is, isotopically, relatively heavy (δ56Fe = 0.045 ±0.101‰; 2SD; n=4; number of chips). We take this variation to suggest that the main group aubrite parent body formed a discreet heavy Fe isotope-enriched core, whilst the Shallowater meteorite is most likely from a different parent body where core and silicate material remixed. This could be due to intensive impact-induced shearing stress, or the ultimate destruction of the Shallowater parent body.

Analysis of separated enstatite meteorite mineral phases show that the magnetic phase (Fe metal) is systematically enriched in the heavier Fe isotopes when compared to non-magnetic phases (Fe hosted in troilite), which agrees with previous experimental observations and theoretical calculations. The difference between magnetic and non-magnetic phases from enstatite achondrites provides an equilibrium metal-sulfide Fe isotopic fractionation factor of Δ56Femetal-troilite = δ56Femetal − δ56Fetroilite of 0.129 ±0.060‰ (2SE) at 1060 ±80K, which confirms the predictions of previous theoretical calculations.

Reference
Wang K, Savage PS, Moynier F (2014) The iron isotope composition of enstatite meteorites: Implications for their origin and the metal/sulfide Fe isotopic fractionation factor. Geochimica et Cosmochimica Acta (In Press).

Link to Article [DOI: 10.1016/j.gca.2014.07.019]

Copyright Elsevier

^1,2Baratoux, D., ^3,4H. Samuel, ⁵C. Michaut, ^3,4M. J. Toplis, ^3,4M. Monnereau, ⁵M. Wieczorek, ^3,6R. Garcia, ⁷K. Kurita

¹Université de Toulouse, UPS-OMP, GET, Toulouse, France
²IRD/Institut Fondamental d’Afrique Noire, Dakar, Senegal
³Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
⁴CNRS; IRAP, Toulouse, France
⁵Institut de Physique du Globe de Paris, Université Paris Diderot, Sorbonne Paris Cité, France
⁶Ecole nationale suprieure de l’aronautique et de l’espace, Toulouse, France
⁷Earthquake Research Institute, University of Tokyo, Tokyo, Japan

New insights into the chemistry of the Martian crust have been made available since the derivation of crustal thickness maps from Mars Global Surveyor gravity and topography data that used a conservative range of density values (2700–3100 kg/m3). A new range of crustal density values is calculated from the major element chemistry of Martian meteorites (3100–3700 kg/m3), igneous rocks at Gusev crater (3100–3600 kg/m3) and from the surface concentration of Fe, Al, Ca, Si, and K measured by the Gamma-Ray Spectrometer on board Mars Odyssey (3250–3450 kg/m3). In addition, the density of mineral assemblages resulting from low-pressure crystallization of primary melts of the primitive mantle are estimated for plausible conditions of partial melting corresponding to the Noachian to Amazonian periods (3100–3300 kg/m3). Despite the differences between these approaches, the results are all consistent with an average density above 3100 kg/m3 for those materials that are close to the surface. The density may be compatible with the measured mass of Mars and the moment of inertia factor, but only if the average crustal thickness is thicker than previously thought (approaching 100 km). A thicker crust implies that crustal delamination and recycling could be possible and may even control its thickness, globally or locally. Alternatively, and considering that geoid-to-topography ratios argue against such a thick crust for the highlands, our results suggest the existence of a buried felsic or anorthositic component in the southern hemisphere of Mars.

Reference
Baratoux D, Samuel H, Michaut C, Toplis MJ, Monnereau M, Wieczorek M, Garcia R, Kurita K (2014), Petrological constraints on the density of the Martian crust, Journal of Geophysical Research Planets, 119.

Link to Article [doi:10.1002/2014JE004642]

Published by arrangement with John Wiley & Sons

¹M. J. Burchell, ¹K. H. McDermott, ¹M. C. Price,¹L. J. Yolland

¹ Centre for Astrophysics and Planetary Science, School of Physical Sciences, Ingram Building, University of Kent, Canterbury, Kent CT2 7NH, UK

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Reference
Burchell MJ, McDermott KH, Price MC, Yolland LJ (2014) Survival of fossils under extreme shocks induced by hypervelocity Impacts. Philosphical Transactions of the Royal Society A, 372: 2023

Link to Article [doi: 10.1098/rsta.2013.0190]

¹ M.A. van Zuilen,¹ P. Philippot,² M.J. Whitehouse,^3,4 A. Lepland

¹ Géobiosphère Actuelle & Primitive, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, UnivParis Diderot, UMR 7154 CNRS, F-75005 Paris, France
² Swedish Museum of Natural History, Box 50007, SE104-05 Stockholm, Sweden
³ Geological Survey of Norway, Leiv Eirikssons vei 39, 7491 Trondheim, Norway
⁴ Tallinn University of Technology, Institute of Geology, 19086 Tallinn, Estonia

Theoretical and experimental studies have shown that atmospheric SO2 isotopologue self-shielding effects in the 190-220 nm region of the solar spectrum are the likely cause for mass independent fractionation of sulfur isotopes (S-MIF). The main products of this photochemical reaction – SO3 and S0 – typically define a compositional array of ca. Δ33S/δ34S = 0.06-0.14. This is at odds with the generally observed trend in Archean sulfides, which broadly defines an array of ca. Δ33S/δ34S = 0.9. Various explanations have been proposed, including a diminution of δ34S caused by chemical and biogenic mass-dependent fractionation of sulfur isotopes (S-MDF), mixing with photolytic products produced during felsic volcanic events, or partial blocking of the low-wavelength part of the spectrum due to the presence of reduced atmospheric gases or an organic haze. Early in Earth history large meteorite impacts would have ejected dust and gas clouds into the atmosphere that shielded solar radiation and affected global climate. It is thus likely that at certain time intervals of high meteorite flux the atmosphere was significantly perturbed, having an effect on atmospheric photochemistry and possibly leaving anomalous sulfur isotopic signatures in the rock record. Here we describe the sulfur isotopic signatures in sulfides of spherule beds S2, S3 and S4 of the Barberton Greenstone Belt, South Africa. In particular, in spherule bed S3 – and to a lesser extent S4 – a trend of ca. Δ33S/δ34S = 0.23 is observed that closely follows the expected trend for SO2-photolysis in the 190-220 nm spectral range. This suggests that an impact dust cloud (deposited as spherule beds), which sampled the higher region of the atmosphere, specifically incorporated products of SO2 photolysis in the 190-220 nm range, and blocked photochemical reactions at higher wavelengths (250-330 nm band). By implication, the generally observed Archaean trend appears to be the result of mixing of different MIF-S sources arising from a variety of photochemical reactions that took place in the lower part of the atmosphere.

Reference
van Zuilen P, Philippot P, Whitehouse MJ, Lepland A (2014) Sulfur Isotope Mass-Independent Fractionation in Impact Deposits of the 3.2 Billion-year-old Mapepe Formation, Barberton Greenstone Belt, South Africa. Geochimica et Cosmochimica Acta (in Press).

Link to Article [DOI: 10.1016/j.gca.2014.07.018]

Copyright Elsevier

¹S. Marchi, ¹W. F. Bottke, ^2,6L. T. Elkins-Tanton, ³M. Bierhaus, ³K. Wuennemann, ⁴A. Morbidelli ⁵D. A. Kring

¹Southwest Research Institute, Boulder, Colorado 80302, USA
²Carnegie Institution for Science, Washington DC 20015, USA
³Museum für Naturkunde, Berlin 10115, Germany
⁴Observatoire de la Côte d’Azur, Nice 06304, France A. Morbidelli
⁵Universities Space Research Association, Lunar and Planetary Institute, Houston, Texas 77058, USA
⁶Present address: School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287, USA

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Reference
Marchi S, Bottke WF, Elkins-Tanton LT, Bierhaus M, Wünnemann K., Morbidelli A, Kring DA (2014) Widespread mixing and burial of Earth’s Hadean crust by asteroid impacts
Nature 511, 578–582

Link to Article [doi:10.1038/nature13539]