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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T. Kohout1,2,¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Department of Physics, University of Helsinki, Helsinki, Finland
²Institute of Geology, Academy of Sciences of the Czech Republic, Prague, Czech Republic

X-ray microtomography (XMT), X-ray diffraction (XRD), and magnetic hysteresis measurements were used to determine micrometeorite internal structure, mineralogy, crystallography, and physical properties at μm resolution. The study samples include unmelted, partially melted (scoriaceous), and completely melted (cosmic spherules) micrometeorites. This variety not only allows comparison of the mineralogy and porosity of these three micrometeorite types but also reveals changes in meteoroid properties during atmospheric entry at various velocities. At low entry velocities, meteoroids do not melt and their physical properties do not change. The porosity of unmelted micrometeorites varies considerably (0–12%) with one friable example having porosity around 50%. At higher velocities, the range of meteoroid porosity narrows, but average porosity increases (to 16–27%) due to volatile evaporation and partial melting (scoriaceous phase). Metal distribution seems to be mostly unaffected at this stage. At even higher entry velocities, complete melting follows the scoriaceous phase. Complete melting is accompanied by metal oxidation and redistribution, loss of porosity (1 ± 1%), and narrowing of the bulk (3.2 ± 0.5 g cm⁻³) and grain (3.3 ± 0.5 g cm⁻³) density range. Melted cosmic spherules with a barred olivine structure show an oriented crystallographic structure, whereas other subtypes do not.

Reference
Kohout et al. (in press) Density, porosity, mineralogy, and internal structure of cosmic dust and alteration of its properties during high-velocity atmospheric entry. Meteoritics & Planetary Science
[doi:10.1111/maps.12325]
Published by arrangement with John Wiley & Sons

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Weiming Cheng, Jiao Wang, Cong Wan

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

Reference
Cheng W, Wang J and Wan C (2014) Morphometric Characterization and Reconstruction Effect Among Lunar Impact Craters. Earth, Moon, and Planets 111:139.

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N. Biver¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France

A spectral survey in the 1 mm wavelength range was undertaken in the long-period comets C/2012 F6 (Lemmon) and C/2013 R1 (Lovejoy) using the 30 m telescope of the Institut de radioastronomie millimétrique (IRAM) in April and November−December 2013. We report the detection of ethylene glycol (CH₂OH)₂ (aGg’ conformer) and formamide (NH₂CHO) in the two comets. The abundances relative to water of ethylene glycol and formamide are 0.2–0.3% and 0.02% in the two comets, similar to the values measured in comet C/1995 O1 (Hale-Bopp). We also report the detection of HCOOH and CH₃CHO in comet C/2013 R1 (Lovejoy), and a search for other complex species (methyl formate, glycolaldehyde).

Reference
Biver et al. (2014) Complex organic molecules in comets C/2012 F6 (Lemmon) and C/2013 R1 (Lovejoy): detection of ethylene glycol and formamide. Astronomy & Astrophysics 566:L50.
[doi:10.1051/0004-6361/201423890]
Reproduced with permission © ESO

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Justin Filiberto^a, Allan H. Treiman^b, Paul A. Giesting^a,c, Cyrena A. Goodrich^d, Juliane Gross^e

^aSouthern Illinois University, Geology Department, Carbondale, IL 62901, USA
^bLunar and Planetary Institute, Houston, TX 77058, USA
^cIllinois State University, Department of Geography–Geology, Normal, IL 61790-4400, USA
^dPlanetary Science Institute, Tucson, AZ 85719, USA
^eAmerican Museum of Natural History, New York, NY 10024, USA

We report scapolite in a melt inclusion in olivine in Nakhla, which is the first occurrence of Cl-scapolite found in a martian meteorite. Using terrestrial metamorphic experiments and modeling we constrain its origin. Cl-rich scapolite in Nakhla is consistent with formation from either a late stage Cl-rich, water-poor magma or magmatic Cl-rich hydrothermal brine at a minimum temperature of 700 °C. The temperature of hydrothermal activity recorded by the Cl-scapolite is significantly higher than the temperatures recorded by alteration minerals in Nakhla, and the fluid was Cl-rich, not CO₂-rich. Our results demonstrate that high-temperature Cl-rich fluids were present within the martian crust, and any potential biologic activity would have to survive in these high temperatures and saline fluids. Halophiles can thrive in NaCl-rich systems but at significantly lower temperatures than those recorded by the scapolite. During cooling of the fluid, the system could have reached a habitable state for halophiles. Importantly, halophiles can survive the conditions of space if they are encased in salt crystals, and therefore chlorine-rich phases present an opportunity to investigate for extant life both on the surface of Mars and in martian meteorites.

Reference
Filiberto J, Treiman AH, Giesting PA, Goodrich CA and Gross J (2014) High-temperature chlorine-rich fluid in the martian crust: A precursor to habitability.  Earth and Planetary Science Letters 401:110.
[doi:10.1016/j.epsl.2014.06.003]
Copyright Elsevier
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Bridges¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Applied Physics Laboratory, Laurel, Maryland, USA

Ventifacts, rocks abraded by wind-borne particles, are found in Gale Crater, Mars. In the eastward drive from “Bradbury Landing” to “Rocknest,” they account for about half of the float and outcrop seen by Curiosity’s cameras. Many are faceted and exhibit abrasion textures found at a range of scales, from submillimeter lineations to centimeter-scale facets, scallops, flutes, and grooves. The drive path geometry in the first 100 sols of the mission emphasized the identification of abrasion facets and textures formed by westerly flow. This upwind direction is inconsistent with predictions based on models and the orientation of regional dunes, suggesting that these ventifact features formed from very rare high-speed winds. The absence of active sand and evidence for deflation in the area indicates that most of the ventifacts are fossil features experiencing little abrasion today.

Reference
Bridges et al. (in press) The rock abrasion record at Gale Crater: Mars Science Laboratory results from Bradbury Landing to Rocknest.  Journal of Geophysical Research: Planets
[doi:10.1002/2013JE004579]
Published by arrangement with John Wiley & Sons
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Marissa J. F. Rosenberg¹, Olivier Berné^2,3 and Christiaan Boersma⁴

¹Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
²Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
³CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
⁴NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035-0001, USA

The mid-infrared (mid-IR; 5–15 μm) spectrum of a wide variety of astronomical objects exhibits a set of broad emission features at 6.2, 7.7, 8.6, 11.3, and 12.7 μm. About 30 years ago it was proposed that these signatures are due to emission from a family of UV heated nanometer-sized carbonaceous molecules known as polycyclic aromatic hydrocarbons (PAHs), causing them to be referred to as aromatic IR bands (AIBs). Today, the acceptance of the PAH model is far from settled, as the identification of a single PAH in space has not yet been successful, and physically relevant theoretical models involving true PAH cross sections do not reproduce the AIBs in detail. In this paper, we use the NASA Ames PAH IR Spectroscopic Database, which contains over 500 quantum-computed spectra, in conjunction with a simple emission model, to show that the spectrum produced by any random mixture of at least 30 PAHs converges to the same kernel-spectrum. This kernel-spectrum captures the essence of the PAH emission spectrum and is highly correlated with observations of AIBs, strongly supporting PAHs as their source. Furthermore, the fact that a large number of molecules are required implies that spectroscopic signatures of the individual PAHs contributing to the AIBs spanning the visible, near-IR, and far-IR spectral regions are weak, explaining why they have not yet been detected. An improved effort, joining laboratory, theoretical, and observational studies of the PAH emission process, will support the use of PAH features as a probe of physical and chemical conditions in the near and distant Universe.

Reference
Rosenberg MJF, Berné O and Boersma C (2014) Random mixtures of polycyclic aromatic hydrocarbon spectra match interstellar infrared emission.  Astronomy & Astrophysics 566:L4.
[doi:10.1051/0004-6361/201423953]
Reproduced with permission © ESO
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