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]
Copyright Elsevier

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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]
Copyright Elsevier

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