Ji Yeon Seok and Aigen Li
Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA

The debris disk around the Vega-type star HD 34700 is detected in dust thermal emission from the near-infrared (IR) to millimeter (mm) and submm wavelength range. Also detected is a distinct set of emission features at 3.3, 6.2, 7.7, 8.6, 11.3, and 12.7µm, which are commonly attributed to polycyclic aromatic hydrocarbon (PAH) molecules. We model the observed dust IR spectral energy distribution (SED) and PAH emission features of the HD 34700 disk in terms of porous dust and astronomical-PAHs. Porous dust together with a mixture of neutral and ionized PAHs closely explains the dust IR SED and PAH emission features observed in the HD 34700 disk. Due to the stellar radiation pressure and Poynting–Robertson drag together with the photodissociation of PAHs, substantial removal of dust and PAHs has occurred in the disk, and continuous replenishment of these materials is required to maintain their current abundances. This implies that these materials are not primitive but secondary products probably originating from mutual collisions among planetesimals, asteroids, and comets.

Reference
Seok JY and Li A (2015)Dust and polycyclic aromatic hydrocarbon in the HD 34700 debris disk. Astrophysical Journal 809:22.
Link to Article [doi:10.1088/0004-637X/809/1/22]

Alyssa K. Cobb^1,2, Ralph E. Pudritz^1,2, and Ben K. D. Pearce^1,2
1Origins Institute, McMaster University, ABB 241, 1280 Main Street, Hamilton, ONL8S 4M1, Canada; alyssacobb107@gmail.com, pudritz@physics.mcmaster.ca, ben.pearce@alumni.ubc.ca
²Department of Physics and Astronomy, McMaster University, ABB 241, 1280 Main Street, Hamilton, ONL8S 4M1, Canada

Carbonaceous chondrite meteorites are known for having high water and organic material contents, including amino acids. Here we address the origin of amino acids in the warm interiors of their parent bodies (planetesimals) within a few million years of their formation, and we connect this with the astrochemistry of their natal protostellar disks. We compute both the total amino acid abundance pattern and the relative frequencies of amino acids within the CM2 (e.g., Murchison) and CR2 chondrite subclasses based on Strecker reactions within these bodies. We match the relative frequencies to well within an order of magnitude among both CM2 and CR2 meteorites for parent body temperatures <200°C. These temperatures agree with 3D models of young planetesimal interiors. We find theoretical abundances of approximately 7 × 105 parts per billion, which is in agreement with the average observed abundance in CR2 meteorites of (4 ± 7) × 105, but an order of magnitude higher than the average observed abundance in CM2 meteorites of (2 ± 2) × 104. We find that the production of hydroxy acids could be favored over the production of amino acids within certain meteorite parent bodies (e.g., CI1, CM2) but not others (e.g., CR2). This could be due to the relatively lower NH3 abundances within CI1 and CM2 meteorite parent bodies, which leads to less amino acid synthesis. We also find that the water content in planetesimals is likely to be the main cause of variance between carbonaceous chondrites of the same subclass. We propose that amino acid abundances are primarily dependent on the ammonia and water content of planetesimals that are formed in chemically distinct regions within their natal protostellar disks.

Reference
Cobb AK, Pudritz RE and Pearce BKD (2015) Nature’s starships. II. Simulating the synthesis of amino acids in meteorite parted bodies. Astrophysical Journal 809:6.
Link to Article [doi:10.1088/0004-637X/809/1/6]

^1,2Asmaa Boujibar, ²Denis Andrault, ²Nathalie Bolfan-Casanova, ²Mohamed Ali Bouhifd, ²Julien Monteux
¹Astromaterials Research and Exploration Science, NASA Johnson Space Center, 2101 Nasa Parkway, Houston, Texas 77058, USA.
²Laboratoire Magmas et Volcans, Université Blaise Pascal, CNRS UMR-6524, 5 rue Kessler, 63000 Clermont-Ferrand, France

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Reference
Boujibar A, Andrault D, Bolfan-Casanova N, Bouhifd MA, Monteux J (2015) Cosmochemical fractionation by collisional erosion during the Earth’s accretion. Nature Communications 6, 8295
Link to Article [doi:10.1038/ncomms9295]

^1,2A. E. Gleason et al. (>10)*
¹Shock and Detonation Physics, Los Alamos National Laboratory, PO Box 1663, Los Alamos, New Mexico 87545, USA Stanford Institute for Materials and Energy Sciences
²SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA

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Reference
A. E. Gleason et al. (2015) Ultrafast visualization of crystallization and grain growth in shock-compressed SiO2. Nature Communications 6, 8191
Link to Article [doi:10.1038/ncomms9191]

^1,2Joanna Gurgurewicz, ^1,3Daniel Mège, ³Véronique Carrère, ³Anne Gaudin, ⁴Joanna Kostylew, ³Yann Morizet, ⁵Peter G. Purcell, ³Laetitia Le Deit
¹Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Wrocław, Podwale St. 75, PL-50449 Wrocław, Poland
²Space Research Centre, Polish Academy of Sciences, Bartycka St. 18A, PL-00716 Warsaw, Poland
³Laboratoire de Planétologie et Géodynamique, UMR CNRS 6112, Université de Nantes, 2 rue de la Houssiniere, 44322 Nantes, France
⁴Institute of Geological Sciences, University of Wrocław, Cybulskiego St. 30, PL-50205 Wrocław, Poland
⁵P&R Geological Consultants, 141 Hastings Street, Scarborough WA 6019, Australia

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Reference
Gurgurewicz J, Mège D, Carrère V, Gaudin A, Kostylew J, Morizet Y, Purcell PG, Le Deit(2015) Inferring alteration conditions on Mars: Insights from near-infrared spectra of terrestrial basalts altered in cold and hot arid Environments. Planetary and Space Science (in Press)
Link to Article [doi:10.1016/j.pss.2015.09.002]

¹Stefanie Brachfeld, ¹Deepa Shah, ²Emily First, ²Julia Hammer, ³Julie Bowles
¹Department of Earth and Environmental Studies, Montclair State University, Montclair, New Jersey, USA
²Department of Geology and Geophysics, University of Hawai‘i, Honolulu, Hawai‘i, USA
³Department of Geosciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA

We evaluate the relationship between the intensity of remanent magnetization and fO2 in natural and synthetic Mars meteorites. The olivine-phyric shergottite meteorite Yamato 980459 (Y-980459) and a sulfur-free synthetic analog (Y-98*) of identical major element composition were analyzed to explore the rock magnetic and remanence properties of a basalt crystallized from a primitive melt, and to explore the role of magmatic and alteration environment fO2 on Mars crustal anomalies. The reducing conditions under which Y-980459 is estimated to have formed (QFM-2.5; Shearer et al. 2006) were replicated during the synthesis of Y-98*. Y-980459 contains pyrrhotite and chromite. Chromite is the only magnetic phase in Y-98*. The remanence-carrying capacity of Y-980459 is comparable to other shergottites that formed in the fO2 range of QFM-3 to QFM-1. The remanence-carrying capacity of these low fO2 basalts is 1–2 orders of magnitude too weak to account for the intense crustal anomalies observed in Mars’s southern cratered highlands. Moderately oxidizing conditions of >QFM-1, which are more commonly observed in nakhlites and Noachian breccias, are key to generating either a primary igneous assemblage or secondary alteration assemblage capable of acquiring an intense remanent magnetization, regardless of the basalt character or thermal history. This suggests that if igneous rocks are responsible for the intensely magnetized crust, these oxidizing conditions must have existed in the magmatic plumbing systems of early Mars or must have existed in the crust during secondary processes that led to acquisition of a chemical remanent magnetization.

Reference
Brachfeld S, Shah D, First E, Hammer J, Bowles J (2015) Influence of redox conditions on the intensity of Mars crustal magnetic anomalies. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12505]
Published by arrangement with John Wiley & Sons

¹Mehmet Yesiltas, ¹Robert E. Peale, ²Miriam Unger, ³Julia Sedlmair,²Carol J. Hirschmugl
¹Department of Physics, University of Central Florida, Orlando, Florida, USA
²Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA
³Forest Products Laboratory, US Department of Agriculture Forest Service, Madison, Wisconsin, USA

Relationships between organic molecules and inorganic minerals are investigated in a single 34 μm diameter grain of the CR2 chondrite Northwest Africa 852 (NWA) 852 with submicron spatial resolution using synchrotron-based imaging micro-FTIR spectroscopy. Correlations based on absorption strength for the various constituents are determined using statistical correlation analysis. The silicate band is found to be correlated with the hydration band, and the latter is highly correlated with stretching modes of aliphatic hydrocarbons. Spatial distribution maps show that water+organic combination, silicate, OH, and C-H distributions overlap, suggesting a possible catalytic role of phyllosilicates in the formation of organics. In contrast, the carbonate band is anticorrelated with water+organic combination, however uncorrelated with any other spectral feature. The average ratio of asymmetric CH2 and CH3 band strengths (CH2/CH3 = 2.53) for NWA 852 is similar to the average ratio of interplanetary dust particles (~2.40) and Wild 2 cometary dust particles (2.50), but it significantly exceeds that of interstellar medium objects (~1.00) and several aqueously altered carbonaceous chondrites (~1.40). This suggests organics of similar length/branching, and perhaps similar formation regions, for NWA 852, Wild 2 dust particles, and interplanetary dust particles. The heterogeneous spatial distribution of ratio values indicates the presence of a mixture of aliphatic organic material with different length/branching, and thus a wide range of parent body processes, which occurred before the considered grain was formed.

Reference
Yesiltas M, Peale RE, Unger M, Sedlmair J, Hirschmugl CJ (2015) Organic and inorganic correlations for Northwest Africa 852 by synchrotron-based Fourier transform infrared microspectroscopy. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12498]
Published by arrangement with John Wiley & Sons

¹R. Terik Daly, ¹Peter H. Schultz 
¹Department of Earth, Environmental and Planetary Sciences, Brown University, 324 Brook St., Box 1846, Providence, RI 02912, United States

Dark material on Vesta may consist of carbonaceous chondrite-like material delivered by impact events. This study uses hypervelocity impact experiments to assess the viability of the impact delivery hypothesis. Experiments reveal that impact events deliver significant fractions of the projectile to the target during impacts at average vestan speeds. Hence, dark material can plausibly be delivered to Vesta by impacts, with the projectile component accumulating in the regolith with time. Projectile retention is sensitive to impact angle, ranging from 7% for 30° impacts (measured from horizontal) to 72% for vertical impacts. Averaged over the probability distribution of impact angles, 17% of the projectile’s mass remains in or near the crater. Projectile-contaminated breccias largely remain inside the crater for vertical impacts. In oblique impacts, projectile-contaminated pieces concentrate downrange beyond the crater rim. Based on experiments, projectile delivery is expected for typical vestan impact conditions, not only for extraordinary events such as low-probability and very low-speed (e.g. <2 km s⁻¹) impacts. These experiments indicate that other (non-dark) impactors contaminate the vestan regolith. Regolith-laden bodies in environments with similar impact speeds also may accrete significant amounts of foreign debris.

Reference
Daly RT, Schultz PH (2015) Delivering a projectile component to the vestan regolith. Icarus 264, 9–19
Link to Article [doi:10.1016/j.icarus.2015.08.034]
Copyright Elsevier

^1,2Tomáš Magna, ¹Nikolaus Gussone, ^1,3Klaus Mezger
¹Institut für Mineralogie, Universität Münster, Corrensstr. 24, D-48149 Münster, Germany
²Czech Geological Survey, Klárov 3, CZ-118 21 Prague, Czech Republic
³Institut für Geologie, Universität Bern, Baltzerstr. 1+3, CH-3012 Bern, Switzerland

New Ca isotope data from a suite of Martian meteorites provide constraints on the Ca isotope composition of the Martian mantle and possible recycling of surface materials back into the mantle. A mean δ44/40Ca of 1.04±0.09‰1.04±0.09‰ (2SD) is estimated for the Martian mantle which can also be taken as an approximation for Bulk Silicate Mars. This value is identical with the estimates for Bulk Silicate Earth, and the inner Solar System planets can therefore be considered homogeneous with respect to Ca isotopes. The Ca isotope composition of two Martian dunites varies by ∼0.3‰∼0.3‰ despite strong chemical and mineralogical similarities and this difference can be caused by the presence of carbonate, probably of pre-terrestrial origin, implying a protracted period of the existence of CaCO3-rich fluids and sufficient amounts of CO2 on the surface of Mars. The variability of δ44/40Ca within the groups of shergottites and nakhlites (clinopyroxene cumulates) cannot be related to partial melting and fractional crystallization in any simple way. However, there is no necessity of incorporating surface lithologies with isotopically light Ca into the mantle sources of Martian meteorites. These inferences are consistent with the absence of large scale crust–mantle recycling and thus of plate tectonics on Mars.

Reference
Magna T, Gussone N, Mezger K (2015) The calcium isotope systematics of Mars. Earth and Planetary Science Letters 430, 86–94
Link to Article [doi:10.1016/j.epsl.2015.08.016]
Copyright Elsevier

¹Haley M. Sapers, ¹Neil R. Banerjee, ²Gordon R. Osinski
¹Centre for Planetary Science and Exploration/Department of Earth Sciences, University of Western Ontario, 1151 Richmond St, London, Ontario, N6A 5B7, Canada
²Department of Physics and Astronomy, University of Western Ontario, 1151 Richmond St, London, Ontario, N6A 5B7, Canada

Here we provide the first high-resolution geochemical evidence for microbial metabolism to be preserved in impact-generated materials. This study is unique as not only do we merge complimentary analytical techniques such as high-resolution spectromicroscopy to assess the biogenicity of tubules in impact glasses, but we compare these results to those from co-occurring abiotic quench crystallites as an intrinsic negative control. Scanning transmission X-ray microscopy (STXM) near edge X-ray absorption fine structure spectroscopy (NEXAFS) at the Fe L3- and C K-edges revealed iron speciation patterns and organic C associated with tubular features in the impact glass. The high spatial resolution of STXM combined with NEXAFS allowed organic carbon to be localized to the tubule features. The fine energy resolution of NEXAFS allowed for unique populations of organic carbon to be spectrally differentiated between the tubule features and the matrix. The distinct and systematic variation in iron redox states observed is consistent with microbially mediated dissimilatory iron reduction. The Ries tubules comprise the first trace fossil preserved in a substrate unique to the impact process, thus illustrating the potential for microbial metabolism to be preserved in impact materials.

Reference
Sapers HM, Banerjee NR, Osinski GR (2015) Potential for impact glass to preserve microbial metabolism. Earth and Planetary Science Letters 430, 95–104
Link to Article [doi:10.1016/j.epsl.2015.08.011]
Copyright Elsevier