T. Hayakawa^1,2, K. Nakamura^2,3, T. Kajino^2,4, S. Chiba^1,5, N. Iwamoto¹, M. K. Cheoun⁶ and G. J. Mathews⁷

¹Japan Atomic Energy Agency, Shirakara-Shirane 2-4, Tokai-mura, Ibaraki 319-1195, Japan
²National Astronomical Observatory, Mitaka, Tokyo 181-8588, Japan
³Waseda University, Ohkubo 3-4-1, Shinjuku, Tokyo 169-8555, Japan
⁴University of Tokyo, Tokyo 113-0033, Japan
⁵Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
⁶Department of Physics, Soongsil University, Seoul 156-743, Korea
⁷Center for Astrophysics, Department of Physics, University of Notre Dame, Notre Dame, IN 46556, USA

The isotope ⁹²Nb decays to ⁹²Zr with a half-life of 3.47 × 10⁷ yr. Although this isotope does not exist in the current solar system, initial abundance ratios for ⁹²Nb/⁹³Nb at the time of solar system formation have been measured in primitive meteorites. The astrophysical origin of this material, however, has remained unknown. In this Letter, we present new calculations which demonstrate a novel origin for ⁹²Nb via neutrino-induced reactions in core-collapse supernovae (ν-process). Our calculated result shows that the observed ratio of ⁹²Nb/⁹³Nb ~10^-5 can be explained by the ν-process.

Reference
Hayakawa T, Nakamura K, Kajino T, Chiba S, Iwamoto N, Cheoun MK and Mathews GJ (in press) Supernova Neutrino Nucleosynthesis of the Radioactive 92Nb Observed in Primitive Meteorites. The Astrophysical Journal – Letters 779:L9.
[doi:10.1088/2041-8205/779/1/L9]

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Martin Jutzi^a and Patrick Michel^b

^aUniversity of Bern, Center for Space and Habitablity, Physics Institute, Sidlerstrasse 5, 3012 Bern, Switzerland
^bLagrange Laboratory, University of Nice Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, B.P. 4229, 06304 Nice Cedex 4, France

In this paper, we investigate numerically the momentum transferred by impacts of small (artificial) projectiles on asteroids. The study of the momentum transfer efficiency as a function of impact conditions and of the internal structure of an asteroid is crucial for performance assessment of the kinetic impactor concept of deflecting an asteroid from its trajectory. The momentum transfer is characterized by the so-called momentum multiplication factor β, which has been been introduced to define the momentum imparted to an asteroid in terms of the momentum of the impactor. Here we present results of code calculations of the βfactor for porous targets, in which porosity takes the form of microporosity and/or macroporosity. The results of our study using a large range of impact conditions indicate that the momentum multiplication factor β is small for porous targets even for very high impact velocities (β<2 for v_imp≤15 km/s), which is consistent with published scaling laws and results of laboratory experiments (Holsapple and Housen, 2012 and Holsapple and Housen, 2013). It is found that both porosity and strength can have a large effect on the amount of transferred momentum and on the scaling of β with impact velocity. On the other hand, the macroporous inhomogeneities considered here do not have a significant effect on β.

Reference
Jutzi M and Michel P (in press) Hypervelocity impacts on asteroids and momentum transfer I. Numerical simulations using porous targets. Icarus
[doi:10.1016/j.icarus.2013.11.020]
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F. Poulet^a, J. Carter^b, J.L. Bishop^c, D. Loizeau^d and S.M. Murchie^e

^aInstitut d’Astrophysique Spatiale, CNRS/Univ. Paris Sud, 91405 Orsay Cedex
^bEuropean Sourthern Observatory, Santiago 19, Chile
^cSETI Institute and NASA Ames Research Center, Mountain View, CA 94043, USA
^dLGLTPE, Université Claude Bernard Lyon1, 69622 Villeurbanne, France
^eJohns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA

A component of the landing site selection process for the Mars Science Laboratory (MSL) involved the presence of of phyllosilicates as the main astrobiological targets. Gale crater was selected as the MSL landing site from among 4 down selected study sites (Gale, Eberswalde and Holden craters, Mawrth Vallis) that addressed the primary scientific goal of assessing the past habitability of Mars. A key constraint on the formation process of these phyllosilicate-bearing deposits is in the precise mineralogical composition. We present a reassessment of the mineralogy of the sites combined with a determination of the modal mineralogy of the major phyllosilicate-bearing deposits of the four final study sites from the modeling of near-infrared spectra using a radiative transfer model. The largest abundance of phyllosilicates (30-70%) is found in Mawrth Vallis, the lowest one in Eberswalde (<25%). Except for Mawrth Vallis, the anhydrous phases (plagioclase, pyroxenes and Martian dust) are the dominant phases, suggesting formation conditions with a lower alteration grade and/or a post-formation mixing with anhydrous phases. The composition of Holden layered deposits (mixture of saponite and micas with a total abundance in the range of 25-45%) suggests transport and deposition of altered basalts of the Noachian crust without major chemical transformation. For Eberswalde, the modal mineralogy is also consistent with detrital clays, but the presence of opaline silica indicates that an authigenic formation occured during the deposition. The overall composition including approximately 20-30% smectite detected by MSL in the rocks of Yellow-knife Bay area interpreted to be material deposited on the floor of Gale crater by channels (http://www.nasa.gov/mission_pages/msl/news/msl20130312.html) is consistent with the compositions modeled for the Eberswalde and Holden deltaic rocks. At Gale, the paucity, the small diversity and the low abundance of nontronite do not favor a complex and long drainage system. Localized aqueous processes in space and time environments could have produced both nontronites and sulfates. However, most materials in Gale are unfortunately dust covered, so that orbital data are limited by spatial resolution and surficial fines that could dilute and obscure the spectral influence of phyllosilicates in the rocks. Potential formation processes of diverse and abundant Mawrth Vallis deposits include low temperature hydrothermal alteration in marine environments and/or pedogenesis.

Reference
Poulet F, Carter J, Bishop JL, Loizeau D and Murchie SM (in press) Mineral abundances at the final four curiosity study sites and implications for their formation. Icarus
[doi:10.1016/j.icarus.2013.11.023]
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David J. Lawrence^1,*, Patrick N. Peplowski¹, Thomas H. Prettyman², William C. Feldman², David Bazell¹, David W. Mittlefehldt³, Robert C. Reedy², Naoyuki Yamashita²

¹The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
²Planetary Science Institute, Tucson, Arizona, USA
³NASA Johnson Space Center, Houston, Texas, USA

Surface composition information from Vesta is reported using fast neutron data collected by the gamma ray and neutron detector on the Dawn spacecraft. After correcting for variations due to hydrogen, fast neutrons show a compositional dynamic range and spatial variability that is consistent with variations in average atomic mass from howardite, eucrite, and diogenite (HED) meteorites. These data provide additional compositional evidence that Vesta is the parent body to HED meteorites. A subset of fast neutron data having lower statistical precision show spatial variations that are consistent with a 400 ppm variability in hydrogen concentrations across Vesta and supports the idea that Vesta’s hydrogen is due to long-term delivery of carbonaceous chondrite material.

Reference
Lawrence DJ, Peplowski PN, Prettyman TH, Feldman W, Bazell D, Mittlefehldt DW, Reedy RC and Yamashita N (in press) Constraints on Vesta’s elemental composition: Fast neutron measurements by Dawn’s gamma ray and neutron detector. Meteoritics & Planetary Science
[doi:10.1111/maps.12187]
Published by arrangement with John Wiley & Sons

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Joel A. Hurowitz^a and Woodward W. Fischer^b

^aDepartment of Geosciences, Stony Brook University, 100 Nicolls Road, Stony Brook, NY 11794-2100, joel.hurowitz@stonybrook.edu, 631-632-6801
^bDivision of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125

The nature of ancient hydrological systems on Mars has been the subject of ongoing controversy, driven largely by a disconnect between observational evidence for flowing water on the Martian surface at multiple scales and the incompatibility of such observations with theoretical models that predict a cold early Martian environment in which liquid water is unstable. Here we present geochemical data from the Mars Exploration Rovers to evaluate the hydrological conditions under which weathering rinds, soils, and sedimentary rocks were formed. Our analysis indicates that the chemistry of rinds and soils document a water-limited hydrologic environment where small quantities of S-bearing fluids enter the system, interact with and chemically alter rock and soil, and precipitate secondary mineral phases at the site of alteration with little to no physical separation of primary and secondary mineral phases. In contrast, results show that the sedimentary rocks of the Burns Formation at Meridiani Planum have a chemical composition well-described as a mixture between siliciclastic sediment and sulfate-bearing salts derived from the evaporation of groundwater. We hypothesize that the former may be derived from the recently investigated Shoemaker Formation, a sequence of impact breccias that underlie the Burns Formation. This result has important implications for the style of chemical weathering and hydrology recorded by these sedimentary materials, revealing long-range transport of ions in solution in an open hydrological system that is consistent only with subsurface or overland flow of liquid water.

Reference
Hurowitz JA and Fischer WW (in press) Contrasting styles of water-rock interaction at the Mars Exploration Rover landing sites. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2013.11.021]
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A.A. Fraeman^a, S.L. Murchie^b, R.E. Arvidson^a, R.N. Clark^c, R.V. Morris^d, A.S. Rivkin^b and F. Vilas^e

^aWashington University in St. Louis, 1 Brookings Dr, Campus Box 1169, St. Louis, MO, 63130, United States
^bThe Johns Hopkins University Applied Physics Laboratory, 11101 Johns Hopkins Road, Laurel, MD, 20723, United States
^cUS Geological Survey, Box25046 Denver Federal Center, Denver, CO 80225, United States
^dARES, NASA Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058, United States
^ePlanetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ, 85719, United States

Absorption features on Phobos and Deimos in the visible / near infrared wavelength region (0.4 – 3.9 μm) are mapped using observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Fe²⁺ electronic absorptions diagnostic of olivine and pyroxene are not detected. A broad absorption centered around 0.65 μm within the red spectral units of both moons is detected, and this feature is also evident in telescopic, Pathfinder, and Phobos-2 observations of Phobos. A 2.8 μm metal-OH combination absorption on both moons is also detected in the CRISM data, and this absorption is shallower in the Phobos blue unit than in the Phobos red unit and Deimos. The strength, position, and shape of both of the 0.65 μm and 2.8 μm absorptions are similar to features seen on red-sloped, low-albedo primitive asteroids. Two end-member hypotheses are presented to explain the spectral features on Phobos and Deimos. The first invokes the presence of highly desiccated Fe-phyllosilicate minerals indigenous to the bodies, and the second invokes Rayleigh scattering and absorption of small iron particles formed by exogenic space weathering processing, coupled with implantation of H from solar wind. Both end-member hypotheses may play a role, and in-situ exploration will be needed to ultimately determine the underlying causes for the pair of spectral features observed on Phobos and Deimos.

Reference
Fraeman AA, Murchie SL, Arvidson RE, Clark RN, Morris RV, Rivkin AS and Vilas F (in press) Spectral Absorptions on Phobos and Deimos in the Visible/Near Infrared Wavelengths and Their Compositional Constraints. Icarus
[doi:10.1016/j.icarus.2013.11.021]
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M. Shyam Prasad^1,*, N. G. Rudraswami¹ and Dipak K. Panda²

¹National Institute of Oceanography, CSIR, Panaji, India
²Physical Research Laboratory, Ahmedabad, India

Flux of micrometeorites is estimated by using cosmic spherule counts from a seafloor area of 2.50 m² from the Indian Ocean. The spherules are recovered from sediment samples in close-spaced locations from the Indian Ocean after sieving 293 kg of sediment. The terrestrial age of the spherules has a range of 0–~50,000 years. The spherules have a size range of 57–750 µm (average size 265 ± 92 µm). The diameter of the spherules increases from scoriaceous-barred-cryptocrystalline-glassy types. The time-averaged flux of the spherules is 160 t/yr, a sizeable mass (>60%) resides in the >300 µm fraction; the slope of distribution is similar to that of Deep-Sea Spherules but significantly different from other collections which have lower average diameters. It is observed here, a significant population of cosmic dust resides in the larger sizes which can be recovered by sampling large areas in time and space. The spherule textures are similar to that of unbiased collections from the polar regions, indicating that the textural types of cosmic dust that have been raining on the Earth during the last 50 kyr have been constant regardless of size. Major element chemistry of a majority of the spherules show elemental ratios that are close to a CM or CI chondritic parent body; a single spherule (0.2% of the population) suggests an achondritic parent body. Unbiased collections spanning large areas temporally and spatially enlarge the inventory of the Earth-crossing meteoroid complex and provide valuable inputs for models on cosmic dust accretion.

Reference
Prasad MS Rudraswami NG and Panda DK (in press) Micrometeorite flux on Earth during the last ~50,000 years. Journal of Geophysical Research – Planets
[doi:10.1002/2013JE004460]
Published by arrangement with John Wiley & Sons

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George Cooper^a, Friedrich Horz^b, Alanna Spees^c and Sherwood Chang^a

^aSpace Science Division, NASA Ames Research Center, Moffett Field, CA 94035, USA
^bAstromaterials Research and Exploration Science, NASA–Johnson Space Center, Houston, TX 77058, USA
^cDepartment of Medical Microbiology and Immunology, University of California, Davis, CA 95616, United States

Multiple missions to search for water-soluble organic compounds on the surfaces of Solar System bodies are either current or planned and, if such compounds were found, it would be desirable to determine their origin(s). Asteroid or comet material is likely to have been components of all surface environments throughout Solar System history. To simulate the survival of meteoritic compounds both during impacts with planetary surfaces and under subsequent (possibly) harsh ambient conditions, we subjected known meteoritic compounds to comparatively high impact–shock pressures (>30 GPa) and/or to extremely oxidizing/corrosive acid solution. Consistent with past impact experiments, α-amino acids survived only at trace levels above ~18 GPa. Polyaromatic hydrocarbons (PAHs) survived at levels of 4–8% at a shock pressure of 36 GPa. Lower molecular weight sulfonic and phosphonic acids (S&P) had the highest degree of impact survival of all tested compounds at higher pressures. Oxidation of compounds was done with a 3:1 mixture of HCl:HNO₃, a solution that generates additional strong oxidants such as Cl₂ and NOCl. Upon oxidation, keto acids and α-amino acids were the most labile compounds with proline as a significant exception. Some fraction of the other compounds, including non-α amino acids and dicarboxylic acids, were stable during 16–18 hours of oxidation. However, S&P quantitatively survived several months (at least) under the same conditions. Such results begin to build a profile of the more robust meteoritic compounds: those that may have survived, i.e., may be found in, the more hostile Solar System environments. In the search for organic compounds, one current mission, NASAʼs Mars Science Laboratory (MSL), will use analytical procedures similar to those of this study and those employed previously on Earth to identify many of the compounds described in this work. The current results may thus prove to be directly relevant to potential findings of MSL and other missions designed for extraterrestrial organic analysis.

Reference
Cooper G, Horz F, Spees A and Chang S (in press) Highly stable meteoritic organic compounds as markers of asteroidal delivery. Earth and Planetary Science Letters
[doi:10.1016/j.epsl.2013.10.021]
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Megumi Matsumoto^a, Kazushige Tomeoka^a, Yusuke Seto^a, Akira Miyake^b, Mitsuhiro Sugita^a

^aDepartment of Earth and Planetary Sciences, Faculty of Science, Kobe University, Kobe 657-8501, Japan
^bDepartment of Geology and Mineralogy, Faculty of Science, Kyoto University, Kyoto 606-8502, Japan

Ningqiang is an ungrouped carbonaceous chondrite that chemically and petrologically resembles CV3 chondrites. The matrix of Ningqiang shows much higher abundances of Na, K, and Al by factors of 4.4, 2.7, and 1.6, respectively, than in CV3 chondrites. Our scanning and transmission electron microscope observations and synchrotron radiation X-ray diffraction measurements reveal that the major proportions of these elements can be attributed to the presence of nepheline and sodalite. Rietveld refinement of X-ray diffraction data shows that the feldspathoids constitute 7.7 vol.% of all crystalline phases in the matrix. Nepheline and sodalite occur mostly as discrete, equidimensional grains 2–5 μm in diameter that are dispersed homogeneously in the matrix. Most of the grains contain inclusions of Fe-rich olivine and minor Ca pyroxene, magnetite, troilite, and pentlandite.
Despite the high abundances of Na, K, and Al in the matrix of Ningqiang, the bulk meteorite abundances of these elements are comparable to those of the CV group (e.g., Rubin et al., 1988). This means that the chondrules, which constitute a major proportion of the volume other than the matrix in Ningqiang, are depleted in Na, K, and Al. In fact, our analyses and observations show that the chondrules in Ningqiang overall contain very small amounts of these elements. Our interpretation of these findings suggests that nepheline and sodalite in the Ningqiang matrix were originally formed by Na-metasomatism of the chondrules and Ca–Al-rich inclusions in the meteorite parent body. Afterward, they were likely disaggregated and scattered into the matrix. However, it is difficult to envisage that the disaggregation and scattering occurred in situ in the present setting of the meteorite. Hence, we suggest that the Ningqiang meteorite underwent these processes before final lithification.

Reference
Matsumoto M, Tomeoka K, Seto Y, Miyake A and Sugita M (in press) Nepheline and sodalite in the matrix of the Ningqiang carbonaceous chondrite: Implications for formation through parent-body processes. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2013.11.016]
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Rebecca J. Thomas^a, David A. Rothery^a, Susan J. Conway^a, Mahesh Anand^a,b

^aDepartment of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, U.K
^bDepartment of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, U.K

Recent images of the surface of Mercury have revealed an unusual and intriguing landform: sub-kilometre scale, shallow, flat-floored, steep-sided rimless depressions typically surrounded by bright deposits and generally occurring in impact craters. These ‘hollows’ appear to form by the loss of a moderately-volatile substance from the planet’s surface and their fresh morphology and lack of superposed craters suggest that this process has continued until relatively recently (and may be on-going). Hypotheses to explain the volatile-loss have included sublimation and space weathering, and it has been suggested that hollow-forming volatiles are endogenic and are exposed at the surface during impact cratering. However, detailed verification of these hypotheses has hitherto been lacking. In this study, we have conducted a comprehensive survey of all MESSENGER images obtained up to the end of its fourth solar day in orbit in order to identify hollowed areas. We have studied how their location relates to both exogenic processes (insolation, impact cratering, and solar wind) and endogenic processes (explosive volcanism and flood lavas) on local and regional scales. We find that there is a weak correlation between hollow formation and insolation intensity, suggesting formation may occur by an insolation-related process such as sublimation. The vast majority of hollow formation is in localised or regional low-reflectance material within impact craters, suggesting that this low-reflectance material is a volatile-bearing unit present below the surface that becomes exposed as a result of impacts. In many cases hollow occurrence is consistent with formation in volatile-bearing material exhumed and exposed during crater formation, while in other cases volatiles may have accessed the surface later through re-exposure and possibly in association with explosive volcanism. Hollows occur at the surface of thick flood lavas only where a lower-reflectance substrate has been exhumed from beneath them, indicating that this form of flood volcanism on Mercury lacks significant concentrations of hollow-forming volatiles.

Reference
Thomas RJ, Rothery DA, Conway SJ and Anand M (in press) Hollows on Mercury: materials and mechanisms involved in their formation. Icarus
[doi:10.1016/j.icarus.2013.11.018]
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