^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]

Corpyright Elsevier

¹E. Charon, ²J. Aléon, ³J.- N. Rouzaud

¹ Centre de Sciences Nucléaires et de Sciences de la Matière, CNRS/IN2P3 – Université Paris Sud XI, UMR CNRS 8609, Bât 104 91405 Orsay Campus, France
² Laboratoire de Géologie, UMR CNRS 8538, Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris Cedex 5, France
³ Present address: CEA Saclay, DSM/IRAMIS/ NIMBE Laboratoire Edifices Nanométriques, Bat 522, 91191 Gif sur Yvette, France

The structure and nanostructures of carbon phases from the Acapulco and Lodran meteorites and their carbon and nitrogen isotopic composition were investigated at the nanometer and micrometer scale using a systematic combination of Raman microspectrometry, high-resolution transmission electron microscopy and secondary ion mass spectrometry to determine their origin and thermal evolution. Several morphological types were recognized belonging to roughly two isotopic and structural families: coarse carbon grains and rosettes on one hand, only found in Acapulco, and vein-like carbon occurrences on the other hand present in both Acapulco and Lodran. Carbon phases in Acapulco are highly graphitized, and show a genetic relationship with metal indicative of metal-assisted graphitization. By contrast, carbon phases in Lodran are exclusively disordered mesoporous turbostratic carbons, in spite of their inclusion in metal and the higher peak temperature experienced by the Lodran parent body. δ13C values range between -59‰ and +37‰ in Acapulco and between -38‰ and -1‰ in Lodran and show in both cases a peak in their distribution at the value of chondritic insoluble organic matter (IOM, -10 to -15‰). N concentrations together with δ15N values indicate a mixing between a component akin to chondritic IOM in Lodran with a δ15N value around +10 – +20‰ and a component akin to that in the most N-poor Acapulco graphites. The latter are systematically depleted in 15N with a δ15N value constant at ∼ -140‰ for N concentrations below ∼ 1.4 wt%.

These observations can be explained if carbon phases in Acapulco and Lodran result from the late impact introduction of CI-CM like IOM, after significant cooling of the parent-body, and subsequent carbonization and graphitization of IOM by interaction with FeNi metal by the heat wave induced by the impact. Temperatures probably reached 900°C in Acapulco, enough to achieve metal-assisted graphitization but were not significantly higher than 650°C in Lodran. Carbon phases in Lodran would have been formed by the secondary carbonization of hydrocarbon fluids released during the primary carbonization of IOM. In the framework of this model, the C isotopic compositions can be reproduced using Rayleigh distillation at each carbonization step and the N isotopic compositions can be understood as resulting from the variable loss and preservation of 15N-rich nitriles (δ15N ∼ +800‰) and 15N-poor pyrroles (δ15N = -140‰) during carbonization. The combined interpretation of the temperatures deduced from this model, petrographic cooling rates, and thermochronological indicators suggest that the CI-CM IOM could have been introduced in the parent-body by an impact, about 10 Myr after solar system formation.

Reference
Charon E, Aléon J., Rouzaud N (2014) Impact delivery of organic matter on the acapulcoite-lodranite parent-body deduced from C, N isotopes and nanostructures of carbon phases in Acapulco and Lodran. Geochimica et Cosmochimica Acta (in Press)

Link to Article [DOI: 10.1016/j.gca.2014.07.009]

Copyright Elsevier

¹Wladimir Neumann, Doris Breuer¹ and Tilman Spohn^1,2

¹ Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Planetenforschung, Planetenphysik, Rutherfordstr. 2, 12489 Berlin, Germany
e-mail: wladimir.neumann@dlr.de
² Institut für of Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany

Aims. Compaction of initially porous material prior to melting is an important process that has influenced the interior structure and the thermal evolution of planetesimals in their early history. On the one hand, compaction decreases the porosity resulting in a reduction of the radius and on the other hand, the loss of porosity results in an increase of the thermal conductivity of the material and thus in a more efficient cooling. Porosity loss by hot pressing is the most efficient process of compaction in planetesimals and can be described by creep flow, which depends on temperature and stress. Hot pressing has been repeatedly modelled using a simplified approach, for which the porosity is gradually reduced in some fixed temperature interval between ≈650 K and 700 K. This approach neglects the dependence of compaction on stress and other factors such as matrix grain size and creep activation energy. In the present study, we compare this parametrised method with a self-consistent calculation of porosity loss via a creep related approach.

Methods. We use our thermal evolution model from previous studies to model compaction of an initially porous body and consider four basic packings of spherical dust grains (simple cubic, orthorhombic, rhombohedral, and body-centred cubic). Depending on the grain packing, we calculate the effective stress and the associated porosity change via the thermally activated creep flow. For comparison, compaction is also modelled by simply reducing the initial porosity linearly to zero between 650 K and 700 K. As we are interested in thermal metamorphism and not melting, we only consider bodies that experience a maximum temperature below the solidus temperature of the metal phase.

Results. For the creep related approach, the temperature interval in which compaction takes place depends strongly on the size of the planetesimal and is not fixed as assumed in the parametrised approach. Depending on the radius, the initial grain size, the activation energy, and the initial porosity and specific packing of the dust grains, the temperature interval lies within 500−1000 K. This finding implies that the parametrised approach strongly overestimates compaction and underestimates the maximum temperature. For the cases considered, the post-compaction porous layer retained at the surface is a factor of 1.5 to 4 thicker for the creep related approach. The difference in the temperature evolution between the two approaches increases with decreasing radius and the maximum temperature can deviate by over 30% for small bodies.

Reference
Neumann W, Breuer D, Spohn T (2014) Modelling of compaction in planetesimals. Astronomy&Astrophysics 567, A120

Link to Article [http://dx.doi.org/10.1051/0004-6361/201423648]

Reproduced with permission © ESO

¹K.M.Stack et al.(<10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Department of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA

The Sheepbed member of the Yellowknife Bay formation in Gale crater contains millimeter-scale nodules that represent an array of morphologies unlike those previously observed in sedimentary deposits on Mars. Three types of nodules have been identified in the Sheepbed member in order of decreasing abundance: solid nodules, hollow nodules, and filled nodules, a variant of hollow nodules whose voids have been filled with sulfate minerals. This study uses Mast Camera (Mastcam) and Mars Hand Lens Imager (MAHLI) images from the Mars Science Laboratory Curiosity rover to determine the size, shape, and spatial distribution of the Sheepbed nodules. The Alpha Particle X-Ray Spectrometer (APXS) and ChemCam instruments provide geochemical data to help interpret nodule origins. Based on their physical characteristics, spatial distribution, and composition, the nodules are interpreted as concretions formed during early diagenesis. Several hypotheses are considered for hollow nodule formation including origins as primary or secondary voids. The occurrence of concretions interpreted in the Sheepbed mudstone and in several other sedimentary sequences on Mars suggests that active groundwater systems play an important role in the diagenesis of Martian sedimentary rocks. When concretions are formed during early diagenetic cementation, as interpreted for the Sheepbed nodules, they have the potential to create a taphonomic window favorable for the preservation of Martian organics.

Reference
Stack KM et al.(2014) Diagenetic origin of nodules in the Sheepbed member, Yellowknife Bay formation, Gale crater, Mars. Journal of Geophysical Research: Planets (in Press)

Link to Article [DOI: 10.1002/2014JE004617]

Published by Arrangement with John Wiley & Sons

R. F. Smith et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers Website.

¹Lawrence Livermore National Laboratory, PO Box 808, Livermore, California 94550, USA

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

Reference
Smith RF et al. (2014) Ramp compression of diamond to five terapascals. Nature 511,330–333

Link to Article [doi:10.1038/nature13526]

Cosmochemistry Papers is appreciated and used by many people around the world. I am glad that two people indicated their interest and are willing to continue this website. I might help out from time to time, but from now on Andreas will be responsible for the site. In a few weeks we will presumably welcome the next member to the team. Thanks for this continuation and all the best!

Dominik & Andreas

K. L. Donaldson Hanna¹, L. C. Cheek¹, C. M. Pieters¹, J. F. Mustard¹, B. T. Greenhagen², I. R. Thomas³ and N. E. Bowles³

¹Department of Geological Sciences, Brown University, Providence, Rhode Island, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
³Atmospheric, Oceanic, and Planetary Physics, University of Oxford, Oxford, UK

Recent advancements in visible to near infrared orbital measurements of the lunar surface have allowed the character and extent of the primary anorthositic crust to be studied at unprecedented spatial and spectral resolutions. Here we assess the lunar primary anorthositic crust in global context using a spectral parameter tool for Moon Mineralogy Mapper data to identify and map Fe-bearing crystalline plagioclase based on its diagnostic 1.25 µm absorption band. This allows plagioclase-dominated rocks, specifically anorthosites, to be unambiguously identified as well as distinguished from lithologies with minor to trace amounts of mafic minerals. Low spatial resolution global mosaics and high spatial resolution individual data strips covering more than 650 targeted craters were analyzed to identify and map the mineralogy of spectrally pure regions as small as ~400 m in size. Spectrally, pure plagioclase is identified in approximately 450 targets located across the lunar surface. Diviner thermal infrared (TIR) data are analyzed for 37 of these nearly monomineralic regions in order to understand the compositional variability of plagioclase (An#) in these areas. The average An# for each spectrally pure region is estimated using new laboratory measurements of a well-characterized anorthite (An₉₆) sample. Diviner TIR results suggest that the plagioclase composition across the lunar highlands is relatively uniform, high in calcium content, and consistent with plagioclase compositions found in the ferroan anorthosites (An_94–98). Our results confirm that spectrally pure anorthosite is widely distributed across the lunar surface, and most exposures of the ancient anorthositic crust are concentrated in regions of thicker crust surrounding impact basins on the lunar nearside and farside. In addition, the scale of the impact basins and the global nature and distribution of pure plagioclase requires a coherent zone of anorthosite of similar composition in the lunar crust supporting its formation from a single differentiation event like a magma ocean. Our identifications of pure anorthosite combined with the GRAIL crustal thickness model suggest that pure anorthosite is currently observed at a range of crustal thickness values between 9 and 63 km and that the primary anorthositic crust must have been at least 30 km thick.

Reference
Donaldson Hanna KL, Cheek LC, Pieters CM, Mustard JF, Greenhagen BT, Thomas IR, and Bowles NE (in press) Global assessment of pure crystalline plagioclase across the Moon and implications for the evolution of the primary crust. Journal of Geophysical Research: Planets
[doi:10.1002/2013JE004476]
Published by arrangement with John Wiley & Sons

Link to Article

I. G. Mitrofanov¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Department of Nuclear Planetology, Institute for Space Research of Russian Academy of Science, Moscow, Russia

The presence of hydrated phases in the soil and near-surface bedrock of Gale Crater is thought to be direct evidence for water-rock interaction in the crater in the ancient past. Layered sediments over the Gale Crater floor are thought to have formed in past epochs due to sediment transport, accumulation, and cementation through interaction with fluids, and the observed strata of water-bearing minerals record the history of these episodes. The first data analysis of the Dynamic Albedo of Neutrons (DAN) investigation on board the Curiosity rover is presented for 154 individual points of active mode measurements along 1900 m of the traverse over the first 361 Martian solar days in Gale crater. It is found that a model of constant water content within subsurface should be rejected for practically all tested points, whereas a two-layer model with different water contents in each layer is supported by the data. A so-called direct two-layer model (water content increasing with depth) yields acceptable fits for odometry ranges between 0 and 455 m and beyond 638 m. The mean water (H₂O) abundances of the top and bottom layers vary from 1.5 to 1.7 wt % and from 2.2 to 3.3 wt %, respectively, while at some tested spots the water content is estimated to be as high as ~5 wt %. The data for odometry range 455–638 m support an inverse two-layer model (water content decreasing with depth), with an estimated mean water abundance of 2.1 ± 0.1 wt % and 1.4 ± 0.04 wt % in the top and bottom layers, respectively.

Reference
Mitrofanov et al. (in press) Water and chlorine content in the Martian soil along the first 1900 m of the Curiosity rover traverse as estimated by the DAN instrument. Journal of Geophysical Research: Planets
[doi:10.1002/2013JE004556]
Published by arrangement with John Wiley & Sons

Link to Article