^1,2,3 Camille Cartier,^1,2,3Tahar Hammouda, ^1,2,3 Maud Boyet,^1,2,3 Mohamed Ali Bouhifd, ^1,2,3 Jean-Luc Devidal

¹ Clermont Université, Université Blaise Pascal, Laboratoire Magmas et Volcans, BP 10448, F-63000 Clermont-Ferrand, France
² CNRS, UMR 6524, LMV, F-63038 Clermont-Ferrand, France
³ IRD, R 163, LMV, F-63038 Clermont-Ferrand, France

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Reference
Cartier C, Hammouda T, Boyet M, Bouhifd MA, DevidalJ-L (2014) Redox control of the fractionation of niobium and tantalum during planetary accretion and core formation. Nature Geoscience 7, 573–576

Link to Articel [doi:10.1038/ngeo2195]

¹E. Asphaug, ^1,2A. Reufer

¹ School of Earth and Space Exploration, Arizona State University, PO Box 876004, Tempe, Arizona 85287, USA
²Physics Institute, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
Asphaug E, Reufer A (2014) Mercury and other iron-rich planetary bodies as relics of inefficient accretion. Nature Geoscience 7, 564–568

Link to Article [doi:10.1038/ngeo2189]

^1,2Masaaki Miyahara, ^1,3Eiji Ohtani, ⁴Akira Yamaguchi, ^1,4Shin Ozawa, ^1,5Takeshi Sakaia, ⁶Naohisa Hirao

¹ Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan;
² Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan;
³ V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090, Russia;
⁴ National Institute of Polar Research, Tokyo 190-8518, Japan;
⁵ Geodynamics Research Center, Ehime University, Matsuyama 790-8577, Japan; and
⁶ Japan Synchrotron Radiation Research Institute, Hyogo 679-5198, Japan

Howardite–eucrite–diogenite meteorites (HEDs) probably originated from the asteroid 4 Vesta. We investigated one eucrite, Béréba, to clarify a dynamic event that occurred on 4 Vesta using a shock-induced high-pressure polymorph. We discovered high-pressure polymorphs of silica, coesite, and stishovite originating from quartz and/or cristobalite in and around the shock-melt veins of Béréba. Lamellar stishovite formed in silica grains through a solid-state phase transition. A network-like rupture was formed and melting took place along the rupture in the silica grains. Nanosized granular coesite grains crystallized from the silica melt. Based on shock-induced high-pressure polymorphs, the estimated shock-pressure condition ranged from ∼8 to ∼13 GPa. Considering radiometric ages and shock features, the dynamic event that led to the formation of coesite and stishovite occurred ca. 4.1 Ga ago, which corresponds to the late heavy bombardment period (ca. 3.8–4.1 Ga), deduced from the lunar cataclysm. There are two giant impact basins around the south pole of 4 Vesta. Although the origin of HEDs is thought to be related to dynamic events that formed the basins ca. 1.0 Ga ago, our findings are at variance with that idea.

Reference
Miyahara M, Ohtani E, Yamaguchi A, Ozawa S, Sakaia T, Hirao N (2014) Discovery of coesite and stishovite in eucrite. Proceedings of the National Academy of Sciences 111, 30.

Link to Article [doi: 10.1073/pnas.1404247111]

¹ Ian B. Hutchinson, ²John Parnell, ^1,3Howell G.M. Edwards, ⁴Jan Jehlick, ⁵Craig P. Marshall, ¹Liam V. Harris, ¹Richard Ingley

¹ Department of Physics and Astronomy, Space Research Centre, University of Leicester, University Road, Leicester LE1 7RH, UK
² Department of Geology & Petroleum Geology, University of Aberdeen, King’s College, Aberdeen AB24 3UE, UK
³ Centre for Astrobiology and Extremophiles Research, School of Life Sciences, University of Bradford, Bradford BD7 1DP, UK
⁴ Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Sciences, Charles University, Albertov 6, 12843 Prague 2, Czech Republic
⁵ Department of Geology, University of Kansas, 1475 Jayhawk Blvd., Lawrence, KS 66045, US

We currently do not have a copyright agreement with this publisher and cannot display the abstract here.

Reference
Hutchinson IB, Parnell J, Edwards HGM, Jehlick J, Marshall CP, Harris LV, Ingley R (2014) Potential for analysis of carbonaceous matter on Mars using Raman spectroscopy. Planetary and Space Science (in Press)
Link to Article [DOI: 10.1016/j.pss.2014.07.006]

¹J. S. Greaves1 et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.
¹ SUPA, Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, UK

Far-infrared Herschel images of the epsilon Eridani system, seen at a fifth of the Sun’s present age, resolve two belts of debris emission. Fits to the 160 μm PACS image yield radial spans for these belts of 12-16 and 54-68 AU. The south end of the outer belt is ≈10% brighter than the north end in the PACS+SPIRE images at 160, 250, and 350 μm, indicating a pericenter glow attributable to a planet “c.” From this asymmetry and an upper bound on the offset of the belt center, this second planet should be mildly eccentric (ec ≈ 0.03-0.3). Compared to the asteroid and Kuiper Belts of the young Sun, the epsilon Eri belts are intermediate in brightness and more similar to each other, with up to 20 km sized collisional fragments in the inner belt totaling ≈5% of an Earth mass. This reservoir may feed the hot dust close to the star and could send many impactors through the Habitable Zone, especially if it is being perturbed by the suspected planet epsilon Eri b, at semi-major axis ≈3 AU

Reference
Greaves JS et al. (>10) (2014) Extreme Conditions in a Close Analog to the Young Solar System: Herschel Observations of Eridani. The Astrophysical Journal Letter, 791 L11

Link to Article [doi:10.1088/2041-8205/791/1/L11]

^1,2Amy L. Fagan, ^1,2,3Katherine H. Joy, ^1,2Donald D. Bogard, ^1,2David A. Kring

¹ Center for Lunar Science and Exploration, Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX, 77058, USA
² NASA Lunar Science Institute, Moffett Field, CA, USA
³ School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Williamson Building, Oxford Road, Manchester, M13 9PL, UK

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Reference
Fagan AL, Joy KH, Bogard DD, Kring DA (2014) Ages of Globally Distributed Lunar Paleoregoliths and Soils from 3.9 Ga to the Present. Earth, Moon, and Planets 112, 1-4, 59-71

Link to Article [10.1007/s11038-014-9437-7]

¹N.A. Starkey, ¹I.A. Franchi, ² M.R. Lee

¹ Planetary and Space Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA
² School of Geographical and Earth Sciences, University of Glasgow, Gregory Building, Lilybank Gardens, Glasgow G12 8QQ, UK

Two interplanetary dust particles (IDPs) investigated by NanoSIMS reveal diverse oxygen isotope compositions at the micrometer-scale. The oxygen isotope values recorded at different locations across the single IDP fragments cover a wider range than the bulk values available from all IDPs and bulk meteorites measured to date. Measurement of H, C, and N isotopes by NanoSIMS, and the use of scanning and transmission electron microscopy (SEM and TEM) to determine elemental compositions and textural information allows for a better understanding of the lithologies and organic signatures associated with the oxygen isotope features.

IDP Balmoral, a ∼15μm-sized fragment with a chondritic porous (CP) -IDP-like texture, contains a region a few micrometers in size characterised by 16O-depleted isotope signatures in the range δ17O, δ18O = +80 to +200 ‰. The remainder of the fragment has a more 16O-rich composition (δ18O = 0-20 ‰), similar to many other IDPs and bulk meteorites. Other than in discrete pre-solar grains, such extreme 16O-depletions have only been observed previously in rare components within the matrix of the Acfer 094 meteorite. However, TEM imaging and FeO/MgO/Si ion ratios indicate that the 16O-depleted regions in Balmoral did not form by the same mechanism as that proposed for the 16O-depleted phases in Acfer 094. As the level of 16O depletion is consistent with that expected from isotope selective self-shielding, it is likely that the 16O-depleted reservoir was located close to that where oxygen self-shielding effects were most pronounced (i.e. the outer solar nebula or even interstellar medium).

Individual regions within IDP Lumley cover a range in δ18O from -30 to +19 ‰, with the oxygen isotope values broadly co-varying with δD, δ13C, δ15N, light-element ratios and texture. The relationships observed in Lumley indicate that the parent body incorporated material at the micrometer-scale from discrete diverse isotopic reservoirs, some of which are represented by inner Solar System material but others which must have formed in the outer Solar System.

The IDP fragments support a model whereby primary dust from the early solar nebula initially formed a variety of reservoirs in the outer solar nebula, with those at lower AU incorporating a higher proportion of inner Solar System chondritic dust than those at larger AU. These reservoirs were subsequently disrupted into micrometer-sized clasts that were re-incorporated into IDP parent bodies, presumably at large AU. These results reveal that any models accounting for mixing processes in the early solar nebula must also account for the presence of an extremely 16O-depleted reservoir in the comet-forming region.

Reference
Starkey NA, Franchi IA, Lee MR (2014) Isotopic diversity in interplanetary dust particles and preservation of extreme 16O-depletion. Geochimica et Cosmochimica Acta (in Press)
Link to Article [DOI: 10.1016/j.gca.2014.07.011]

Copyright Elsevier

^1,2D. A. Nedelcu, ^2,1M. Birlan, ^1,2M. Popescu, ¹O. Bădescu and ¹D. Pricopi

¹ Astronomical Institute of the Romanian Academy, 5 Cuţitul de Argint, 040557 Bucharest, Romania
e-mail: nedelcu@aira.astro.ro; mpopescu@aira.astro.ro; octavian@aira.astro.ro; dpricopi@aira.astro.ro
² Institut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE), Observatoire de Paris, 77 avenue Denfert-Rochereau, 75014 Paris Cedex, France
e-mail: mirel.birlan@imcce.fr

Aims. In this paper we report near-infrared spectroscopic observations of one of the largest potentially hazardous asteroids, (214869) 2007 PA8. Mineralogical analysis of this object was followed by the investigation of the dynamical delivery mechanism from its probable source region, based on long-term numerical integrations.

Methods. The spectrum of (214869) 2007 PA8 was analysed using the positions of 1 μm and 2 μm bands and by curve-matching with RELAB meteorites spectra. Its dynamical evolution was investigated by means of a 200 000-year numerical integration in the past of 1275 clones followed to the source region.

Results. (214869) 2007 PA8 has a very young surface with a composition more akin to H chondrites than to any other type of ordinary chondrite. It arrived from the outer Main Belt in the near-Earth space via the 5:2 mean motion resonance with Jupiter by eccentricity pumping. Identification of its source region far from (6) Hebe raises the possibility of the existence of a second parent body of the H chondrites that has a radically different post-accretion history. Future spectroscopic surveys in the 5:2 resonance region will most likely discover other asteroids with an H chondrite composition.

Reference
Nedelcu DA, Birlan M, Popescu M, Bădescu O, Pricopi D. (2014) Evidence for a source of H chondrites in the outer main asteroid belt. Astrophysics&Astronomy Letters 567, L7
Link to Article [http://dx.doi.org/10.1051/0004-6361/201423949]

Reproduced with permission © ESO

^1,2P. R. McCullough, ^1,3N. Crouzet, ^4,5D. Deming, and ^6,7N. Madhusudhan

¹ Space Telescope Science Institute, Baltimore, MD 21218, USA
² Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
³ Dunlap Institute for Astronomy & Astrophysics, University of Toronto, 50 St. George Street, Toronto, Ontario M5S 3H4, Canada
⁴ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
⁵ NASA Astrobiology Institute’s Virtual Planetary Laboratory
⁶ Yale Center for Astronomy & Astrophysics, Yale University, New Haven, CT 06511, USA
⁷ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK

We report near-infrared spectroscopy of the gas giant planet HD 189733b in transit. We used the Hubble Space Telescope Wide Field Camera 3 (HST WFC3) with its G141 grism covering 1.1 μm to 1.7 μm and spatially scanned the image across the detector at 2” s–1. When smoothed to 75 nm bins, the local maxima of the transit depths in the 1.15 μm and 1.4 μm water vapor features are, respectively, 83 ± 53 ppm and 200 ± 47 ppm greater than the local minimum at 1.3 μm. We compare the WFC3 spectrum with the composite transit spectrum of HD 189733b assembled by Pont et al., extending from 0.3 μm to 24 μm. Although the water vapor features in the WFC3 spectrum are compatible with the model of non-absorbing, Rayleigh-scattering dust in the planetary atmosphere, we also re-interpret the available data with a clear planetary atmosphere. In the latter interpretation, the slope of increasing transit depth with shorter wavelengths from the near infrared, through the visible, and into the ultraviolet is caused by unocculted star spots, with a smaller contribution of Rayleigh scattering by molecular hydrogen in the planet’s atmosphere. At relevant pressures along the terminator, our model planetary atmosphere’s temperature is ~700 K, which is below the condensation temperatures of sodium- and potassium-bearing molecules, causing the broad wings of the spectral lines of Na I and K I at 0.589 μm and 0.769 μm to be weak.

Reference
McCullough RP, Crouzet N, Deming D, Madhusudhan N (2014) Water Vapor in the Spectrum of the Extrasolar Planet HD 189733b. I. The Transit. The Astrophysical Journal 791, 55.

Link to Article: [doi:10.1088/0004-637X/791/1/55]

^1,2O. Poch, ¹S. Kaci, ¹F. Stalport, ³C. Szopa, ^1,4P. Coll

¹ LISA, UMR CNRS 7583, Université Paris Est Créteil, Université Paris Diderot, Institut Pierre Simon Laplace, 61 avenue du Général de Gaulle, 94010 Créteil cedex, France
² Center for Space and Habitability, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland
³ Université Versailles St-Quentin;Sorbonne Universités, UPMC Univ. Paris 06;CNRS/INSU, LATMOS-IPSL, Quartier des Garennes, 11 Boulevard d’Alembert, 78230 Guyancourt, France
⁴ Institut Universitaire de France, 103 bld St-Michel, 75005 Paris, France

The search for organic carbon at the surface of Mars, as clues of past habitability or remnants of life, is a major science goal of Mars’ exploration. Understanding the chemical evolution of organic molecules under current Martian environmental conditions is essential to support the analyses performed in situ. What molecule can be preserved? What is the timescale of organic evolution at the surface? This paper presents the results of laboratory investigations dedicated to monitor the evolution of organic molecules when submitted to simulated Mars surface ultraviolet radiation (190-400 nm), mean temperature (218 ± 2 K) and pressure (6 ± 1 mbar) conditions. Experiments are done with the MOMIE simulation setup (for Mars Organic Molecules Irradiation and Evolution) allowing both a qualitative and quantitative characterization of the evolution the tested molecules undergo ( Poch et al., 2013). The chemical structures of the solid products and the kinetic parameters of the photoreaction (photolysis rate, half-life and quantum efficiency of photodecomposition) are determined for glycine, urea, adenine and chrysene. Mellitic trianhydride is also studied in order to complete a previous study done with mellitic acid ( Stalport et al., 2009), by studying the evolution of mellitic trianhydride. The results show that solid layers of the studied molecules have half-lives of 10 to 103 hours at the surface of Mars, when exposed directly to Martian UV radiation. However, organic layers having aromatic moieties and reactive chemical groups, as adenine and mellitic acid, lead to the formation of photoresistant solid residues, probably of macromolecular nature, which could exhibit a longer photostability. Such solid organic layers are found in micrometeorites or could have been formed endogenously on Mars. Finally, the quantum efficiencies of photodecomposition at wavelengths from 200 to 250 nm, determined for each of the studied molecules, range from 10-2 to 10-6 molecule photon-1 and apply for isolated molecules exposed at the surface of Mars. These kinetic parameters provide essential inputs for numerical modeling of the evolution of Mars’ current reservoir of organic molecules. Organic molecules adsorbed on Martian minerals may have different kinetic parameters and lead to different endproducts. The present study paves the way for the interpretation of more complex simulation experiments where organics will be mixed with Martian mineral analogs.

Reference
Poch O, Kaci S, Stalport F, Szopa C, Coll P (2014) Laboratory insights into the chemical and kinetic evolution of several organic molecules under simulated Mars surface UV radiation conditions. Icarus (in Press)

Link to Article [DOI: 10.1016/j.icarus.2014.07.014]

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