Indhu Varatharajan, Neeraj Srivastava and Sripada V.S. Murty

PLANEX, Physical Research Laboratory, Ahmedabad 380009, India

A comparative assessment of the mineralogy of young basalts (~1.2 Ga to ~2.8 Ga) from the western nearside, Moscoviense basin, and the Orientale basin of the Moon has been made using Level 2 Moon Mineralogy Mapper (M³) data from the Chandrayaan-1 mission. Spectral data characteristics of the individual units have been generated from fresh small craters to minimize the complications due to space weathering. Representative spectra for individual units and the derived spectral parameters (Band centers and Integrated Band Depth Ratio) have been used to study composition of these young basalts. A modified approach of Gaffey et al. (2002) (for olivine-pyroxene mixtures) and the methodology of Adams (1974) (for interpreting pyroxene type) have been used to improve our understanding of the spectral behavior of these basalts. Most of the young basalts of Oceanus Procellarum are characterized by abundant olivines and they show complex volcanic history. Vast exposures of olivine concentrated units having higher abundance of olivine content than high-Ca pyroxenes are emplaced in the northern Oceanus Procellarum region. Mostly, they show distinct stratigraphic gradation with the immediately underlying units of relatively lower olivine content. The Moscoviense unit shows signatures of Fe-rich glasses along with clinopyroxenes. The basalts of Orientale basin are typically devoid of olivine and are rich in high-Ca pyroxene. Thus, mineralogy of these mare basalts which erupted during the late stage volcanism vary across the Moon’s surface; however, broader observations reveal apparently higher FeO content in the younger basalts of western nearside and Orientale region.

Reference
Varatharajan I, Srivastava N and Murty SVS (in press) Mineralogy of young lunar mare basalts: Assessment of temporal and spatial heterogeneity using M3 data from Chandrayaan-1. Icarus
[doi:10.1016/j.icarus.2014.03.045]
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Kévin Baillié and Sébastien Charnoz

Laboratoire AIM-LADP, Université Paris Diderot/CEA/CNRS, F-91191 Gif sur Yvette, France

Observations of protoplanetary disks show that some characteristics seem recurrent, even in star formation regions that are physically distant such as surface mass density profiles varying as r⁻¹ or aspect ratios of about 0.03–0.23. Accretion rates are also recurrently found around 10⁻⁸–10⁻⁶ M_☉ yr⁻¹ for disks that have already evolved. Several models have been developed in order to recover these properties. However, most of them usually simplify the disk geometry if not its mid-plane temperature. This has major consequences for modeling the disk evolution over millions of years and consequently planet migration. In the present paper, we develop a viscous evolution hydrodynamical numerical code that simultaneously determines the disk photosphere geometry and the mid-plane temperature. We then compare our results of long-term simulations with similar simulations of disks with a constrained geometry along the Chiang & Goldreich prescription (d lnH/d lnr = 9/7). We find that the constrained geometry models provide a good approximation of the disk surface density evolution. However, they differ significantly regarding the temperature–time evolution. In addition, we find that shadowed regions naturally appear at the transition between viscously dominated and radiation-dominated regions that falls in the region of planetary formation. We show that χ (photosphere height to pressure scale height ratio) cannot be considered a constant, which is consistent with the findings of Watanabe & Lin. Comparisons with observations show that all disks naturally evolve toward a shallow surface density disk (Σ∝r⁻¹). The mass flux across the disk typically stabilizes in about 1 Myr.

Reference
Baillié K and Charnoz C (2014) Time Evolution of a Viscous Protoplanetary Disk with a Free Geometry: Toward a More Self-consistent Picture. The Astrophysical Journal 786:35.
[doi:10.1088/0004-637X/786/1/35]

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Marian Horstmann and Addi Bischoff

Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany

On October 7, 2008, a small asteroid named 2008 TC₃ was detected in space about 19 h prior to its impact on Earth. Numerous world-wide observations of the object while still in space allowed a very precise determination of its impact area: the Nubian Desert of northern Sudan, Africa. The asteroid had a pre-atmospheric diameter of ~4 m; its weight is reported with values between ~8 and 83 t, and the bulk density with ~2–3 g/cm³, translating into a bulk porosity in the range of ~20–50%. Several dedicated field campaigns in the predicted strewn field resulted in the recovery of more than 700 (monolithological) meteorite fragments with a total weight of ~0.5 kg. These meteorites were collectively named “Almahata Sitta”, after the nearby train station 6, and initially classified as an anomalous polymict ureilite. Further work, however, showed that Almahata Sitta is not only a ureilite but a complex polymict breccia containing chemically and texturally highly variable meteorite fragments, including different ureilites, a ureilite-related andesite, metal-sulfide assemblages related to ureilites, and various chondrite classes (enstatite, ordinary, carbonaceous, Rumuruti-like). It was shown that that chondrites and ureilites derive from one parent body, i.e., asteroid 2008 TC₃, making this object, in combination with the remotely sensed physical parameters, a loosely aggregated, rubble-pile-like object. Detailed examinations have been conducted and mineral-chemical data for 110 samples have been collected, but more work on the remaining samples is mandatory.
Detailed study of Almahata Sitta allows insights into the formation and evolution of ureilites and their parent body. These results support the catastrophic impact disruption of the ureilite parent body and re-accretion of the dispersed ureilitic material into second generation ureilite asteroids. Almahata Sitta shows that different chondritic materials were present in the region of re-accretion and mixed into the newly formed rubble-pile-like asteroid. Asteroid 2008 TC₃ was part of a late-formed ureilitic second generation body in the main belt and was liberated ∼20 Ma ago, finally moving into Earth-crossing orbits that ultimately led to its impact on Earth. The abundant samples of Almahata Sitta, fragments of Asteroid 2008 TC₃, allow study of not only different types of meteorites, but offer the unique opportunity to gain further insights into processes in the asteroid belt of our Solar System such as migration, collision, mixing, and (re-)accretion of asteroidal bodies. Beyond that, this event has the potential to further the understanding of the meteorite–asteroid links, which is a major goal of meteorite science.

Reference
Horstmann M and Bischoff A (in press) The Almahata Sitta polymict breccia and the late accretion of asteroid 2008 TC3. Chemie der Erde
[doi:10.1016/j.chemer.2014.01.004]
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Heather B. Franz^1,2 et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Center for Research and Exploration in Space Science and Technology, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
²Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland 20742, USA

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

Reference
Franz et al. (in press) Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars. Nature
[doi:10.1038/nature13175]

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Robert V. Wagner and Mark S. Robinson

School of Earth and Space Exploration, Arizona State University, 1100 S. Cady Mall, Tempe, AZ 85287-3603

Lunar Reconnaissance Orbiter Camera images reveal the presence of steep-walled pits in mare basalt (n=8), impact melt deposits (n=221), and highland terrain (n=2). Pits represent evidence of subsurface voids of unknown extents. By analogy with terrestrial counterparts, the voids associated with mare pits may extend for hundreds of meters to kilometers in length, thereby providing extensive potential habitats and access to subsurface geology. Because of their small sizes relative to the local equilibrium crater diameters, the mare pits are likely to be post-flow features rather than volcanic skylights. The impact melt pits are indirect evidence both of extensive subsurface movement of impact melt and of exploitable sublunarean voids. Due to the small sizes of pits (mare, highland, and impact melt) and the absolute ages of their host materials, it is likely that most pits formed as secondary features.

Reference
Wagner RV and Robinson MS (in press) Distribution, Formation Mechanisms, and Significance of Lunar Pits. Icarus
[doi:10.1016/j.icarus.2014.04.002]
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Elisa V. Quintana^1,2 and Jack J. Lissauer²

¹SETI Institute, 189 Bernardo Avenue, Suite 100, Mountain View, CA 94043, USA
²Space Science and Astrobiology Division 245-3, NASA Ames Research Center, Moffett Field, CA 94035, USA

Models of planet formation have shown that giant planets have a large impact on the number, masses, and orbits of terrestrial planets that form. In addition, they play an important role in delivering volatiles from material that formed exterior to the snow line (the region in the disk beyond which water ice can condense) to the inner region of the disk where terrestrial planets can maintain liquid water on their surfaces. We present simulations of the late stages of terrestrial planet formation from a disk of protoplanets around a solar-type star and we include a massive planet (from 1 M_⊕ to 1 M_J) in Jupiter’s orbit at ~5.2 AU in all but one set of simulations. Two initial disk models are examined with the same mass distribution and total initial water content, but with different distributions of water content. We compare the accretion rates and final water mass fraction of the planets that form. Remarkably, all of the planets that formed in our simulations without giant planets were water-rich, showing that giant planet companions are not required to deliver volatiles to terrestrial planets in the habitable zone. In contrast, an outer planet at least several times the mass of Earth may be needed to clear distant regions of debris truncating the epoch of frequent large impacts. Observations of exoplanets from radial velocity surveys suggest that outer Jupiter-like planets may be scarce, therefore, the results presented here suggest that there may be more habitable planets residing in our galaxy than previously thought.

Reference
Quintana EV and Lissauer JJ (2014) The Effect of Planets Beyond the Ice Line on the Accretion of Volatiles by Habitable-zone Rocky Planets. The Astrophysical Journal 786:33.
[doi:10.1088/0004-637X/786/1/33]

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Karen E. Smith^A, Michael P. Callahan^b, Perry A. Gerakines^b, Jason P. Dworkin^b, Christopher H. House^a

^aDepartment of Geosciences and Penn State Astrobiology Research Center, Pennsylvania State University, 220 Deike Building, University Park, PA 16802, USA
^bSolar System Exploration Division and the Goddard Center for Astrobiology, National Aeronautics and Space Administration Goddard Space Flight Center, Gr

The distribution and abundances of pyridine carboxylic acids (including nicotinic acid) in eight CM2 carbonaceous chondrites (ALH 85013, DOM 03183, DOM 08003, EET 96016, LAP 02333, LAP 02336, LEW 85311, and WIS 91600) were investigated by liquid chromatography coupled to UV detection and high resolution Orbitrap mass spectrometry. We find that pyridine monocarboxylic acids are prevalent in CM2-type chondrites and their abundance negatively correlates with the degree of pre-terrestrial aqueous alteration that the meteorite parent body experienced. We also report the first detection of pyridine dicarboxylic acids in carbonaceous chondrites. Additionally, we carried out laboratory studies of proton-irradiated pyridine in carbon dioxide-rich ices (a 1:1 mixture) to serve as a model of the interstellar ice chemistry that may have led to the synthesis of pyridine carboxylic acids. Analysis of the irradiated ice residue shows that a comparable suite of pyridine mono- and dicarboxylic acids was produced, although aqueous alteration may still play a role in the synthesis (and ultimate yield) of these compounds in carbonaceous meteorites. Nicotinic acid is a precursor to nicotinamide adenine dinucleotide, a likely ancient molecule used in cellular metabolism in all of life, and its common occurrence in CM2 chondrites may indicate that meteorites may have been a source of molecules for the emergence of more complex coenzymes on the early Earth.

Reference
Smith KE, Callahan MP, Gerakines PA, Dworkin JP and House CH (in press) Investigation of Pyridine Carboxylic Acids in CM2 Carbonaceous Chondrites: Potential Precursor Molecules for Ancient Coenzymes. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2014.04.001]
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J. Steinacker^1,2, C. W. Ormel³, M. Andersen¹ and A. Bacmann¹

¹UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, 38041 Grenoble, France
²Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
³Astronomy Department, University of California, Berkeley, CA 94720, USA

Context. With the initial steps of the star formation process in the densest part of the interstellar medium (ISM) still under debate, much attention is paid to the formation and evolution of pre-stellar cores. The recently discovered coreshine effect can aid in exploring the core properties and in probing the large grain population of the ISM.
Aims. We discuss the implications of the coreshine detected from the molecular cloud core L1506C in the Taurus filament for the history of the core and the existence of a primitive ISM component of large grains becoming visible in cores.
Methods. The coreshine surface brightness of L1506C is determined from Spitzer IRAC images at 3.6 μm. We perform grain growth calculations to estimate the grain size distribution in model cores similar in gas density, radius, and turbulent velocity to L1506C. Scattered light intensities at 3.6 μm are calculated for a variety of MRN and grain growth distributions using the DIRBE 3.5 μm all-sky map as external interstellar radiation field, and are compared to the observed coreshine surface brightness.}
Results. For a core with the overall physical properties of L1506C, no detectable coreshine is predicted with a size distribution following the shape and size limits of an MRN distribution. Extending the distribution to grain radii of about 0.65 μm allows to reproduce the observed surface brightness level in scattered light. Assuming the properties of L1506C to be preserved, models for the growth of grains in cores do not yield sufficient scattered light to account for the coreshine within the lifetime of the Taurus complex. Only increasing the core density and the turbulence amplifies the scattered light intensity to a level consistent with the observed coreshine brightness.
Conclusions. The coreshine observed from L1506C requires the presence of grains with sizes exceeding the common MRN distribution. The grains could be part of primitive omni-present large grain population becoming visible in the densest part of the ISM, could grow under the turbulent dense conditions of former cores, or in L1506C itself. In the later case, L1506C must have passed through a period of larger density and stronger turbulence. This would be consistent with the surprisingly strong depletion usually attributed to high column densities, and with the large-scale outward motion of the core envelope observed today.

Reference
Steinacker J, Ormel CW, Andersen M and Bacmann A (2014) Coreshine in L1506C – Evidence for a primitive big-grain component or indication for a turbulent core history? Astronomy & Astrophysics 564:A96.
[doi:10.1051/0004-6361/201322117]
Reproduced with permission © ESO

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A. Garenne^a, P. Beck^a, G. Montes-Hernandez^b, R. Chiriac^c, F. Toche^c, E. Quirico^a, L. Bonal^a and B. Schmitt^a

^aCNRS and University Joseph Fourier, IPAG, OSUG/INSU, BP 53, 38041 Grenoble Cedex 9, France
^bCNRS, ISTerre, F-38041 Grenoble, France
^cUniversité de Lyon, Université Lyon 1, Laboratoire des Multimatériaux et Interfaces UMR CNRS 5615, 22 Avenue Gaston Berger, 69622 Villeurbanne Cedex, France.

Carbonaceous chondrites record processes of aqueous alteration in the presence of hydrated and hydroxylated minerals, which could have provided a source of water in the inner solar system (Alexander et al., 2012, 2013; Trigo-Rodriguez and Martin-Torres, 2011). In this study, thermogravimetric analysis (TGA) was performed on 26 CM chondrites, which cover a range of degree of aqueous alteration from 2.0, such as Meteorite Hills (MET) 01070, to 2.6, such as Queen Alexandra Range (QUE) 97990, in order to quantify their water content. In addition, by measuring the release of volatile elements as a function of temperature, we obtained information on the mineralogy of water-bearing phases and provide indicators of aqueous alteration based on water released by phyllosilicates. These analyses are combined with infrared spectroscopy (IR) made on meteorite pellets heated up to 300°C. The infrared features (-OH band at 3-μm and SiO₄ around 10-μm) revealed a correlation with TGA. The two techniques are in agreement with the scheme of aqueous alteration proposed by Rubin et al. (2007) and Alexander et al. (2013) based on phyllosilicate abundance.
The low temperature (200-400°C) mass loss observed in TGA is attributed to Fe-oxy-hydroxydes (ferrihydrite, goethite). However, the proportion of these minerals formed by terrestrial alteration remains unknown. TGA also revealed two anomalous CM chondrites, Pecora Escarpment (PCA) 02012 and PCA 02010. Their TGA curves are significantly different from those of “regular” CMs with little mass loss, which can be related to the dehydration history of these meteorites in response to a heating event (Raman measurements also point toward a thermal event, Quirico et al., 2013). In the case of more mildly heated chondrites, such as with Wisconsin Range (WIS) 91600, the TGA curve presents similar mass loss to the other CMs.
Seven bulk measurements of CR chondrites and 3 measurements of matrix-enriched parts of CR meteorites were also studied by TGA, and confirm the low hydration level of chondrules and a significant alteration of the matrix. The water content of the matrix of the CM 2.6 QUE 97990 was estimated and compared to TGA of the matrix enriched portion of the CR2 EET 92159 and that of Orgueil.
Results suggest a similar aqueous alteration degree between Orgueil and the matrix of CMs (around 25 wt%) and a lower alteration of the CR2 matrix (11 wt% of H₂O).

Reference
Garenne A, Beck P, Montes-Hernandez G, Chiriac R, Toche F, Quirico E, Bonal L and B. Schmitt B (in press) The abundance and stability of “water” in type 1 and 2 carbonaceous chondrites (CI, CM and CR). Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2014.03.034]
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K. Stephan¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹DLR, Institute of Planetary Research, Berlin, Germany

Small morphologically fresh impact craters (<10 km in diameter) on Vesta’s surface with a photometrically distinct ejecta blanket are expected to represent fresh surface material and thus provide the opportunity to study the composition of the unweathered surface. Dawn-Framing Camera and Visual and Infrared Spectrometer (VIR) data reveal impact craters with bright, dark, and mixed, i.e., partly bright and dark, ejecta existing on Vesta’s surface, which not only differ in the visible albedo from their surroundings but also in their composition. Differences in the composition are related to the visible albedo and/or the geographic location of the impact craters. Bright ejecta, only seen in the southern Vestan hemisphere, are dominated by howardite/eucrite-like material as expected for Vesta’s upper crust. Dark ejecta associated with dark impact craters are dominated by a strongly absorbing, spectrally neutral compound, supporting an origin from carbon-rich impactors. Few impact craters of intermediate albedo in Vesta’s southern hemisphere contain material resembling diogenites, which are expected to exist in the deeper parts of Vesta’s interior. The geological settings suggest that the diogenite-like material represents a part of a layer of diogenitic material surrounding the Rheasilvia basin or local concentrations of diogenitic material as part of the ejecta excavated during the latter stage of the Rheasilvia impact event. The spectral differences between eucrite- and diogenite-dominated materials also could be verified due to spin-forbidden absorptions in the visible spectral range, which are known from laboratory spectra of pyroxenes, but, which have been identified in the VIR spectra of Vesta for the first time.

Reference
Stephan et al. (in press) Small fresh impact craters on asteroid 4 Vesta: A compositional and geological fingerprint. Journal of Geophysical Research: Planets
[doi:10.1016/j.gca.2014.03.034]
Published by arrangement with John Wiley & Sons

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