Pablo Sobron^1,2,3, Janice L. Bishop^1,3, David F. Blake³, Bin Chen³ and Fernando Rull⁴

¹SETI Institute, 189 Bernardo Avenue, Mountain View, California 94043, U.S.A.
²MalaUva Labs, 822 Allen Avenue, St. Louis, Missouri 63104, U.S.A.
³NASA Ames Research Center, Moffett Field, California 94035, U.S.A.
⁴Unidad Asociada UVA-Centro de Astrobiología, Edificio INDITI, Av.Francisco Valles 8, Parque Tecnologico de Boecillo, Parcela 203, Boecillo 47151, Spain

We have characterized complex iron- and sulfate-bearing samples from Rio Tinto (Spain) using X-ray diffraction (XRD), visible-near infrared reflectance (VNIR) spectroscopy, and laser Raman spectroscopy (LRS). Samples were collected for this study from the Peña de Hierro region of Rio Tinto because this site represents a natural acidic environment that is a potential analog for such environments on Mars. We report an evaluation of the capabilities of these three techniques in performing detailed mineralogical characterization of potential Mars-like samples from a natural acidic terrestrial environment. Sulfate minerals found in these samples include gypsum, jarosite, and copiapite, and iron hydroxide bearing minerals found include goethite and ferrihydrite. These sulfate and iron hydroxide/oxyhydroxide minerals were detected by XRD, VNIR, and LRS. Minor quartz was identified in some samples by XRD as well, but was not identified using VNIR spectroscopy. Coordinating the results from these three techniques provides a complete picture of the mineralogical composition of the samples. Field instruments were used for this study to mimic the kinds of analyses that could be performed in the field or on martian rovers.

Reference
Sobron P, Bishop JL, Blake DF, Chen B and Rull F (2014) Natural Fe-bearing oxides and sulfates from the Rio Tinto Mars analog site: Critical assessment of VNIR reflectance spectroscopy, laser Raman spectroscopy, and XRD as mineral identification tools. American Mineralogist 99:1199.
[doi:10.2138/am.2014.4595]
Copyright: The Mineralogical Society of America

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A. A. Pavlov¹, A. K. Pavlov^2,3, V. M. Ostryakov³, G. I. Vasilyev², P. Mahaffy¹ and A. Steele⁴

¹Planetary Environments Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
²A. F. Ioffe Physico-Technical Institute of Russian Academy of Sciences, St. Petersburg, Russia
³St. Petersburg State Polytechnical University, St. Petersburg, Russia
⁴Geophysical Laboratory, Carnegie Institute of Washington, Washington, District of Columbia, USA

¹³C/¹²C and ¹⁵N/¹⁴N isotopic ratios are pivotal for our understanding of the Martian carbon cycle, history of the Martian atmospheric escape, and origin of the organic compounds on Mars. Here we demonstrate that the carbon and nitrogen isotopic composition of the surface rocks on Mars can be significantly altered by the continuous exposure of Martian surface to cosmic rays. Cosmic rays can effectively produce ¹³C and¹⁵N isotopes via spallation nuclear reactions on oxygen atoms in various Martian rocks. We calculate that in the top meter of the Martian rocks, the rates of production of both ¹³C and ¹⁵N due to galactic cosmic rays (GCRs) exposure can vary within 1.5–6 atoms/cm³/s depending on rocks’ depth and chemical composition. We also find that the average solar cosmic rays can produce carbon and nitrogen isotopes at a rate comparable to GCRs in the top 5–10 cm of the Martian rocks. We demonstrate that if the total carbon content in a surface Martian rock is <10 ppm, then the “light,” potentially “biological” ¹³C/¹²C ratio would be effectively erased by cosmic rays over 3.5 billion years of exposure. We found that for the rocks with relatively short exposure ages (e.g., 100 million years), cosmogenic changes in ¹⁵N/¹⁴N ratio are still very significant. We also show that a short exposure to cosmic rays of Allan Hills 84001 while on Mars can explain its high-temperature heavy nitrogen isotopic composition (¹⁵N/¹⁴N). Applications to Martian meteorites and the current Mars Science Laboratory mission are discussed.

Reference
Pavlov AA, Pavlov AK, Ostryakov VM, Vasilyev GI, Mahaffy P and Steele A (in press) Alteration of the carbon and nitrogen isotopic composition in the Martian surface rocks due to cosmic ray exposure. Journal of Geophysical Research: Planets
[doi:10.1002/2014JE004615]
Published by arrangement with John Wiley & Sons

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Bruce G. Bills, Sami W. Asmar, Alexander S. Konopliv, Ryan S. Park, Carol A. Raymond

Jet Propulsion Laboratory, California Institute of Technology,Pasadena, CA 91109

We examine the gravity and topography of the asteroid 4 Vesta, as recently revealed by the Dawn mission. The observed gravity is highly correlated with the observed topography, and suggests little lateral variation in density. The variance spectra of both gravity and topography follow power laws which are very similar to those seen for the Moon, Mars, Venus, and Earth. A significant way in which Vesta differs from these larger silicate bodies is that both gravity and topography are significantly anisotropic, with more north-south variation than east-west variation. Rapid rotation plausibly contributes to this anisotropy, but only at harmonic degree two. The remainder of the anisotropy appears related to the large impacts which formed the Rheasilvia and Veneneia basins. We note that, as usual, gravitational inverse problems are non-unique. While the observed gravity and topography of Vesta do not preclude existance of a metallic core, they certainly do not require it.

Reference
Bills BG, Asmar SW, Konopliv AS, Park RS and Raymond CA (in press) Harmonic and statistical analyses of the gravity and topography of Vesta. Icarus
[doi:10.1016/j.icarus.2014.05.033]
Copyright Elsevier

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H. Jönsson¹, N. Ryde¹, G. M. Harper², M. J. Richter³ and K. H. Hinkle⁴

¹Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University, Box 43, SE-221 00 Lund, Sweden
²School of Physics, Trinity College, Dublin 2, Ireland
³Physics Department, University of California, Davis, CA 95616, USA
⁴National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726, USA

The origin of “cosmic” fluorine is uncertain, but there are three proposed production sites/mechanisms for the origin: asymptotic giant branch (AGB) stars, ν nucleosynthesis in Type II supernovae, and/or the winds of Wolf-Rayet stars. The relative importance of these production sites has not been established even for the solar neighborhood, leading to uncertainties in stellar evolution models of these stars as well as uncertainties in the chemical evolution models of stellar populations. We determine the fluorine and oxygen abundances in seven bright, nearby giants with well determined stellar parameters. We use the 2.3 μm vibrational-rotational HF line and explore a pure rotational HF line at 12.2 μm. The latter has never been used before for an abundance analysis. To be able to do this, we have calculated a line list for pure rotational HF lines. We find that the abundances derived from the two diagnostics agree. Our derived abundances are well reproduced by chemical evolution models including only fluorine production in AGB stars and, therefore, we draw the conclusion that this might be the main production site of fluorine in the solar neighborhood. Furthermore, we highlight the advantages of using the 12 μm HF lines to determine the possible contribution of the ν process to the fluorine budget at low metallicities where the difference between models including and excluding this process is dramatic.

Reference
Jönsson H, Ryde N, Harper GM, Richter MJ and Hinkle KH (2014) Fluorine in the Solar Neighborhood: Is It All Produced in Asymptotic Giant Branch Stars? The Astrophysical Journal Letters 789:L41.
[doi:10.1088/2041-8205/789/2/L41]

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M. Laneuville^a, M.A. Wieczorek^a, D. Breuer^b, J. Aubert^a, G. Morard^c, T. Rückriemen^b

^aInstitut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, Case 7011, 35 rue Hélène Brion, 75205 Paris Cedex 13, France
^bInstitute of Planetary Research, German Aerospace Center (DLR), 6 Rutherfordstraße 2, 12489 Berlin, Germany
^cInstitut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC), Sorbonne Universités – UPMC Univ Paris 06, UMR CNRS 7590, Muséum National d’Histoire Naturelle, IRD UMR 206, 4 Place Jussieu, F-75005 Paris, France

The Moon does not possess an internally generated magnetic field at the present day, but extensive evidence shows that such a field existed between at least 4.2 and 3.56 Ga ago. The existence of a metallic lunar core is now firmly established, and we investigate the influence of inner core growth on generating a lunar core dynamo. We couple the results of a 3-D spherical thermochemical convection model of the lunar mantle to a 1-D thermodynamic model of its core. The energy and entropy budget of the core are computed to determine the inner core growth rate and its efficiency to power a dynamo. Sulfur is considered to be the main alloying element and we investigate how different sulfur abundances and initial core temperatures affect the model outcomes. For reasonable initial conditions, a solid inner core between 100 and 200 km is always produced. During its growth, a surface magnetic field of about 0.3 μT is generated and is predicted to last several billion years. Though most simulations predict the existence of a core dynamo at the present day, one way to stop magnetic field generation when the inner core is growing is by a transition between a bottom–up and top–down core crystallization scheme when the sulfur content becomes high enough in the outer core. According to this hypothesis, a model with about 6 to 8 wt.% sulfur in the core would produce a 120–160 km inner core and explain the timing of the lunar dynamo as constrained by paleomagnetic data.

Reference
Laneuville M, Wieczorek MA, Breuer D, Aubert J, Morard G and Rückriemen T (in press) A long-lived lunar dynamo powered by core crystallization. Earth and Planetary Science Letters
[doi:10.1016/j.epsl.2014.05.057]
Copyright Elsevier

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Ilya G. Usoskin^a and Gennady A. Kovaltsov^b

^aReSoLVE Center of Excellence and Sodankylä Geophysical Observatory (Oulu unit) University of Oulu, Finland
^bIoffe Physical-Technical Institute, St.Petersburg, Russia

A mysterious increase of radiocarbon ¹⁴C ca. 775 AD in the Earth’s atmosphere has been recently found by Miyake et al. (Nature, 486, 240, 2012). A possible source of this event has been discussed widely, the most likely being an extreme solar energetic particle event. A new exotic hypothesis has been presented recently by Liu et al. (Sci. Rep., 4, 3728, 2014) who proposed that the event was caused by a cometary impact on Earth bringing additional ¹⁴C to the atmosphere. Here we calculated a realistic mass and size of such a comet to show that it would have been huge (≈100 km across and 10¹⁷-10²⁰ gram of mass) and would have produced a disastrous geological/biological impact on Earth. The absence of an evidence for such a dramatic event makes this hypothesis invalid.

Reference
Usoskin IG and Kovaltsov GA (in press) The carbon-14 spike in the 8th century was not caused by a cometary impact on Earth. Icarus
[doi:10.1016/j.icarus.2014.06.009]
Copyright Elsevier

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Shinya Wanajo¹, Yuichiro Sekiguchi², Nobuya Nishimura³, Kenta Kiuchi², Koutarou Kyutoku⁴ and Masaru Shibata²

¹iTHES Research Group, RIKEN, Wako, Saitama 351-0198, Japan
²Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502, Japan
³Astrophysics, EPSAM, Keele University, Keele ST5 5BG, UK
⁴Department of Physics, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, WI 53201, USA

Recent studies suggest that binary neutron star (NS-NS) mergers robustly produce heavy r-process nuclei above the atomic mass number A ~ 130 because their ejecta consist of almost pure neutrons (electron fraction of Y_e < 0.1). However, the production of a small amount of the lighter r-process nuclei (A  90-120) conflicts with the spectroscopic results of r-process-enhanced Galactic halo stars. We present, for the first time, the result of nucleosynthesis calculations based on the fully general relativistic simulation of a NS-NS merger with approximate neutrino transport. It is found that the bulk of the dynamical ejecta are appreciably shock-heated and neutrino processed, resulting in a wide range of Y_e (0.09-0.45). The mass-averaged abundance distribution of calculated nucleosynthesis yields is in reasonable agreement with the full-mass range (A  90-240) of the solar r-process curve. This implies, if our model is representative of such events, that the dynamical ejecta of NS-NS mergers could be the origin of the Galactic r-process nuclei. Our result also shows that radioactive heating after ~1 day from the merging, which gives rise to r-process-powered transient emission, is dominated by the β-decays of several species close to stability with precisely measured half-lives. This implies that the total radioactive heating rate for such an event can be well constrained within about a factor of two if the ejected material has a solar-like r-process pattern.

Reference
Wanajo S, Sekiguchi Y, Nishimura N, Kiuchi K, Kyutoku K and Shibata M (2014) Production of All the r-process Nuclides in the Dynamical Ejecta of Neutron Star Mergers. The Astrophysical Journal Letters 789:L39.
[doi:10.1088/2041-8205/789/2/L39]

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