P. Thebault¹, Q. Kral¹ and J.-C. Augereau²

¹LESIA-Observatoire de Paris, CNRS, UPMC Univ. Paris 6, Univ. Paris-Diderot, France
²Université Joseph Fourier/CNRS, LAOG, UMR5571, Grenoble, France

Context. In most debris discs, dust grain dynamics is strongly affected by stellar radiation pressure. Because this mechanism is size-dependent, we expect dust grains to be spatially segregated according to their sizes. However, because of the complex interplay between radiation pressure, grain processing by collisions, and dynamical perturbations, this spatial segregation of the particle size distribution (PSD) has proven difficult to investigate and quantify with numerical models.
Aims. We propose to thoroughly investigate this problem by using a new-generation code that can handle some of the complex coupling between dynamical and collisional effects. We intend to explore how PSDs behave in both unperturbed discs at rest and in discs pertubed by planetary objects.
Methods. We used the DyCoSS code to investigate the coupled effect of collisions, radiation pressure, and dynamical perturbations in systems that have reached a steady-state. We considered two setups: a narrow ring perturbed by an exterior planet, and an extended disc into which a planet is embedded. For both setups we considered an additional unperturbed case without a planet. We also investigated the effect of possible spatial size segregation on disc images at different wavelengths.
Results. We find that PSDs are always spatially segregated. The only case for which the PSD follows a standard dn ∝ s^-3.5ds law is for an unperturbed narrow ring, but only within the parent-body ring itself. For all other configurations, the size distributions can strongly depart from such power laws and have steep spatial gradients. As an example, the geometrical cross-section of the disc is very rarely dominated by the smallest grains on bound orbits, as it is expected to be in standard PSDs in s^q with q ≤ −3. Although the exact profiles and spatial variations of PSDs are a complex function of the set-up that is considered, we are still able to derive some reliable results that will be useful for image or SED-fitting models of observed discs.

Reference
Thebault P, Kral Q and Augereau J-C (2014) Grain size segregation in debris discs. Astronomy & Astrophysics 561:A16.
[doi:10.1051/0004-6361/201322052]
Reproduced with permission © ESO

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Natalia A. Konovalova^1,*, Jose M. Madiedo², Josep M. Trigo-Rodríguez³

¹Institute of Astrophysics of the Academy of Sciences of the Republic of Tajikistan, Dushanbe, Tajikistan
²Facultad de Ciencias Experimentales, Universidad de Huelva, Huelva, Spain
³Facultat de Ciencies, Institute of Space Sciences (CSIC-IEEC), Campus UAB, Belaaterra, Spain

The results of the atmospheric trajectory, radiant, heliocentric orbit, and preliminary strewn field calculations for an extremely bright slow-moving fireball are presented. In the evening hours of July 23, 2008, a bright object entered Earth’s atmosphere over Tajikistan. The fireball had a −20.3 maximum absolute magnitude and a spectacularly long persistent dust trail remained visible over a widespread region of Tajikistan for about 28 minutes after sunset. The fireball was also recorded by a visible-light satellite system at 14 h 45 min 25 s UT, and the dust trail was imaged by video and photocameras. A unique aspect of this event is that it was detected by two infrasound and five seismic stations too. The bolide was first recorded at a height of 38.2 km, reached its maximum brightness at a height of 35.0 km, and finished at a height of 19.6 km. The first breakup occurred under an aerodynamic pressure of approximately 1.6 MPa, similar to the values derived for breakups of the scarcely reported meteorite-dropping bolides. The fireball’s trajectory and dynamic results suggest that meteorite survival is likely. The meteoroid followed an Apollo-like asteroid orbit comparable to those derived for previously recovered meteorites with accurately known orbits.

Reference
Konovalova NA, Madiedo JM and Trigo-Rodríguez JM (in press) The Tajikistan superbolide of July 23, 2008. I. Trajectory, orbit, and preliminary fall data. Meteoritics & Planetary Science
[doi:10.1111/maps.12217]
Published by arrangement with John Wiley & Sons

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Philippe Rousselot¹, Olivier Pirali², Emmanuël Jehin³, Michel Vervloet², Damien Hutsemékers³, Jean Manfroid³, Daniel Cordier¹, Marie-Aline Martin-Drumel², Sébastien Gruet², Claude Arpigny³, Alice Decock³, and Olivier Mousis¹

¹Institut UTINAM-UMR CNRS 6213, Observatoire des Sciences de l’Univers THETA, University of Franche-Comté, BP 1615, F-25010 Besançon Cedex, France
²Synchrotron SOLEIL, ligne AILES, UMR 8214 CNRS, L’orme des Merisiers, Saint-Aubin, F-91192 Gif-Sur-Yvette, France
³Département d’Astrophysique, de Géophysique et d’Océanographie, Université de Liège, Allée du Six Aohat ut, B-4000 Liège, Belgium

Determination of the nitrogen isotopic ratios in different bodies of the solar system provides important information regarding the solar system’s origin. We unambiguously identified emission lines in comets due to the ¹⁵NH₂ radical produced by the photodissociation of ¹⁵NH₃. Analysis of our data has permitted us to measure the ¹⁴N/¹⁵N isotopic ratio in comets for a molecule carrying the amine (–NH) functional group. This ratio, within the error, appears similar to that measured in comets in the HCN molecule and the CN radical, and lower than the protosolar value, suggesting that N₂ and NH₃ result from the separation of nitrogen into two distinct reservoirs in the solar nebula. This ratio also appears similar to that measured in Titan’s atmospheric N₂, supporting the hypothesis that, if the latter is representative of its primordial value in NH₃, these bodies were assembled from building blocks sharing a common formation location.

Reference
Rousselot P, Pirali O, Jehin E, Vervloet M, Hutsemékers D, Manfroid J, Cordier D, Martin-Drumel M-A, Gruet S, Arpigny C, Decock A and Mousis O (2014) Toward a Unique Nitrogen Isotopic Ratio in Cometary Ices. The Astrophysical Journal – Letters 780:L17.
[doi:10.1088/2041-8205/780/2/L17]

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L. O’Rourke¹, D. Bockelée-Morvan², N. Biver², B. Altieri¹, D. Teyssier¹, L. Jorda³, V. Debout², C. Snodgrass⁴, M. Küppers¹, M. A’Hearn⁵, T. G. Müller⁶ and T. Farnham⁵

¹European Space Astronomy Centre, ESAC, ESA, 28691 Villanueva de la Cañada, Spain
²LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France
³Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille), UMR 7326, 13388 Marseille, France
⁴Max Planck Institute for Solar System Research, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
⁵Dept. of Astronomy, Univ. of Maryland, College Park, MD 20742-2421, USA
⁶Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany

Context. The sungrazer comet C/2012 S1 (ISON) (perihelion at r_h = 0.0125 AU from the Sun) was bright and active when discovered in September 2012 at 6.3 AU from the Sun.
Aims. Our goal was to characterize the distant gaseous and dust activity of this comet, inbound, from observations of H₂O, CO and the dust coma in the far-infrared and submillimeter domains.
Methods. We report observations undertaken with the Herschel space observatory on 8 and 13 March 2013 (r_h = 4.54–4.47AU) and with the 30 m telescope of Institut de Radioastronomie Millimétrique (IRAM) in March and April 2013 (r_h = 4.45–4.18 AU). The HIFI instrument aboard Herschel was used to observe the H₂O 1₁₀ − 1₀₁ line at 557 GHz, whereas images of the dust coma at 70 μm and 160 μm were acquired with the PACS instrument. Spectra acquired at the IRAM 30 m telescope cover the CO J(2–1) line at 230.5 GHz. The spectral observations were analysed with excitation and radiative transfer models. A model of dust thermal emission taking into account a range of dust sizes is used to analyse the PACS maps.
Results. While H₂O was not detected in our 8 March 2013 observation, we derive a sensitive 3σ upper limit of Q_H2O < 3.5 × 10²⁶ molecules s^-1 for this date. A marginal 3.2σdetection of CO is found, corresponding to a CO production rate of Q_CO = 3.5 × 10²⁷ molecules s^-1. The Herschel PACS measurements show a clear detection of the coma and tail in both the 70 μm and 160 μm maps. Under the assumption of a 2-km radius nucleus, we infer dust production rates in the range 10–13 kg s^-1 or 40–70 kg s^-1, depending on whether a low or high gaseous activity from the nucleus surface is assumed. We constrain the size distribution of the emitted dust by comparing PACS 70 and 160 μm data, and considering optical data. Size indices between –4 and –3.6 are suggested. The morphology of the tail observed on 70 μm images can be explained by the presence of grains with ages older than 60 days.

Reference
O’Rourke L, Bockelée-Morvan D, Biver N, Altieri B, Teyssier D, Jorda L, Debout V, Snodgrass C, Küppers M, A’Hearn M, Müller TG and Farnham T (2013) Herschel and IRAM-30 m observations of comet C/2012 S1 (ISON) at 4.5 AU from the Sun. Astronomy & Astrophysics 560:A101.
[doi:10.1051/0004-6361/201322756]
Reproduced with permission © ESO

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Patrick Lajeunesse^1,*, Guillaume St-Onge², Jacques Locat³, Mathieu J. Duchesne⁴, Michael D. Higgins⁵, Richard Sanfaçon⁶, Joseph Ortiz⁷

¹Centre d’études nordiques and Département de géographie, Université Laval, Québec City, Québec, Canada
²Canada Research Chair in Marine Geology, Institut des sciences de la mer de Rimouski and GEOTOP, Université du Québec à Rimouski, Rimouski, Québec, Canada
³Département de géologie et de génie géologique, Université Laval, Québec City, Québec, Canada
⁴Natural Resources Canada, Geological Survey of Canada, Québec City, Québec, Canada
⁵Sciences de la Terre, Université du Québec à Chicoutimi, Saguenay, Québec, Canada
⁶Canadian Hydrographic Service, Institut Maurice-Lamontagne, Mont-Joli, Québec, Canada
⁷Department of Geology, Kent State University, Kent, Ohio, USA

We report on a 4.1 (±0.2) km diameter and 185 m deep circular submarine structure exposed on the seabed in >40 m water depths in the northwestern Gulf of St. Lawrence (Eastern Canada) from the analysis of high-resolution multibeam bathymetric and seismic data. The presence of a circular form characterized by a central uplift and concentric rings resembles the morphology and geometry of complex meteorite impact structures. Also, other origins, such as kimberlites, intrusions, karsts, or diapirs, can be eliminated on geological criteria. A single 4 cm long breccia fragment recovered from the central uplift has numerous glassy droplets of fluorapatite composition, assumed to be impact melts, and a single quartz grain with planar intersection features thought to be shock-induced planar deformation features (PDFs). The absolute age of this possible impact structure is unknown, but its geological setting indicates that it was formed long after the Mid-Ordovician and before regional pre-Quaternary sea-level lowstands. Present results outline the need for further examination to confirm an impact origin and to precisely date the formation of the structure.

Reference
Lajeunesse P, St-Onge G, Locat J, Duchesne MJ, Higgins MD, Sanfaçon R and Ortiz J (in press) The Corossol structure: A possible impact crater on the seafloor of the northwestern Gulf of St. Lawrence, Eastern Canada. Meteoritics & Planetary Science
[doi:10.1111/maps.12224]
Published by arrangement with John Wiley & Sons

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O. Pravdivtseva^1,*, A. Meshik¹, C. M. Hohenberg¹, G. Kurat^2,†

¹McDonnell Center for the Space Sciences and Physics Department of Washington University, Saint Louis, Missouri, USA
²Department of Lithospheric Sciences, University of Vienna, Vienna, Austria
^†Deceased

Using in situ laser analyses of a polished thin section from the IAB iron meteorite Campo del Cielo, we identified two silicate grains rich in radiogenic ^129*Xe, Cr-diopside, and oligoclase, excavated them from the metal, and irradiated them with thermal neutrons for I-Xe dating. The release profiles of ^129*Xe and ^128*Xe are consistent with these silicates being diopside and oligoclase, with activation energies, estimated using Arrhenius plots, of ∼201 and ∼171 kcal mole⁻¹, respectively. The 4556.4 ± 0.4 Ma absolute I-Xe age of the more refractory diopside isyounger than the 4558.0 ± 0.7 Ma I-Xe age of the less refractory oligoclase. We suggest that separate impact events at different locations and depths on a porous initial chondritic IAB parent body led to the removal of the melt and recrystallization of diopside and oligoclase at the times reflected by their respective I-Xe ages. The diopside and oligoclase grains were later brought into the studied inclusion by a larger scale catastrophic collision that caused breakup and reassembly of the debris, but did not reset the I-Xe ages dating the first events. The metal melt most probably was <1250 °C when it surrounded studied silicate grains. This reassembly could not have occurred earlier than the I-Xe closure in diopside at 4556.4 ± 0.4 Ma.

Reference
Pravdivtseva O, Meshik A, Hohenberg CM and Kurat G (in press) I-Xe ages of Campo del Cielo silicates as a record of the complex early history of the IAB parent body. Meteoritics & Planetary Science
[doi:10.1111/maps.12233]
Published by arrangement with John Wiley & Sons

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A. Garufi¹, S. P. Quanz¹, H. Avenhaus¹, E. Buenzli^{2, 3}, C. Dominik⁴, F. Meru¹, M. R. Meyer¹, P. Pinilla^{5, 6}, H. M. Schmid¹ and S. Wolf⁷

¹Institute for Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
²Department of Astronomy and Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
³Max-Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁴Sterrenkundig Instituut Anton Pannekoek, Science Park 904, 1098 XH Amsterdam, The Netherlands
⁵Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
⁶Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁷University of Kiel, Institute of Theoretical Physics and Astrophysics, Leibnizstrasse 15, 24098 Kiel, Germany

Context. Transitional disks represent a short stage of the evolution of circumstellar material. Studies of dust grains in these objects can provide pivotal information on the mechanisms of planet formation. Dissimilarities in the spatial distribution of small (μm−size) and large (mm−size) dust grains have recently been pointed out.
Aims. Constraints on the small dust grains can be obtained by imaging the distribution of scattered light at near-infrared wavelengths. We aim at resolving structures in the surface layer of transitional disks (with particular emphasis on the inner 10−50 AU), thus increasing the scarce sample of high-resolution images of these objects.
Methods. We obtained VLT/NACO near-IR high-resolution polarimetric differential imaging observations of SAO 206462 (HD 135344B). This technique allows one to image the polarized scattered light from the disk without any occulting mask and to reach an inner working angle of ~0.1″.
Results. A face-on disk is detected in H and K_s bands between 0.1″ and 0.9″. No significant differences are seen between the H and K_s images. In addition to the spiral arms, these new data allow us to resolve for the first time an inner disk cavity for small dust grains. The cavity size (≃28 AU) is much smaller than what is inferred for large dust grains from (sub-)mm observations (39 to 50 AU). This discrepancy cannot be ascribed to any resolution effect.
Conclusions. The interaction between the disk and potential orbiting companion(s) can explain both the spiral arm structure and the discrepant cavity sizes for small and large dust grains. One planet may be carving out the gas (and, thus, the small grains) at 28 AU, and generating a pressure bump at larger radii (39 AU), which holds back the large grains. We analytically estimate that, in this scenario, a single giant planet (with a mass between 5 and 15 M_J) at 17 to 20 AU from the star is consistent with the observed cavity sizes.

Reference
Garufi A, Quanz SP, Avenhaus H, Buenzli E, Dominik C, Meru F, Meyer MR, Pinilla P, Schmid HM and Wolf S (2013) Small vs. large dust grains in transitional disks: do different cavity sizes indicate a planet? SAO 206462 (HD 135344B) in polarized light with VLT/NACO. Astronomy & Astrophysics 560:A105.
[doi:10.1051/0004-6361/201322429]
Reproduced with permission © ESO

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A. S. Pilski^1,*, J. T. Wasson², A. Muszyński³, R. Kryza⁴, Ł. Karwowski⁵ and M. Nowak³

¹Nicolaus Copernicus Museum, Frombork, Poland
²Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, USA
³Institute of Geology, Adam Mickiewicz University, Poznań, Poland
⁴Institute of Geological Sciences, University of Wrocław, Wrocław, Poland
⁵Faculty of Earth Sciences, University of Silesia, Sosnowiec, Poland

Differences in texture and discovery location prompted us to analyze 16 irons from Morasko; one from Seeläsgen, known to have a similar composition; and a new mass found at Jankowo Dolne. These were analyzed in duplicate by instrumental neutron-activation analysis (INAA). The results show that all 18 samples have very similar compositions, distinct from all other IAB irons except Burgavli; we conclude that they are all from a single shower. Eight of the samples were from regions with large amounts of cohenite (but were largely free of inclusions) and six were from samples with very little cohenite; we could find no resolvable difference in composition between these sets, a fact that suggests that the C contents of the metal phases were similar in the two areas. Although Morasko has been classified into the IAB main group (IAB-MG), its Ir plots well outside the main group field on an Ir-Au diagram. We considered the possibility that the low Ir reflected contamination by a melt from a IAB region that ponded and experienced fractional crystallization; however, because Morasko has Pt, W, and Ga values that are the same as the highest values in IAB-MG, we rejected this model. We therefore conclude that Morasko formed from a different melt than the IAB-MG irons; the Morasko melt was produced by impact heating, but one or more of the main Ir carriers did not melt, leaving much of the Ir in the unmelted residue. Copper is the only element that shows resolvable differences among Morasko samples. Most (13 of 18) samples have 149 ± 4 μg g⁻¹ Cu, but three have 213 ± 10 μg g⁻¹; we interpret this to mean that the low-Cu samples have equilibrated with a Cu-rich phase, whereas there was none of the latter phase within a few diffusion lengths of the samples with high Cu contents.

Reference
Pilski AS, Wasson JT, Muszyński A, Kryza R, Karwowski Ł and Nowak M (in press) Low-Ir IAB irons from Morasko and other locations in central Europe: One fall, possibly distinct from IAB-MG. Meteoritics & Planetary Science
[doi:10.1111/maps.12225]
Published by arrangement with John Wiley & Sons

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Thomas S. Kruijer^1,2,*, Peter Sprung^1,2, Thorsten Kleine², Ingo Leya³, Rainer Wieler¹

¹ETH Zürich, Institute of Geochemistry and Petrology, Zürich, Switzerland
²Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Münster, Germany
³Space Research and Planetary Sciences, University of Bern, Bern, Switzerland

Cadmium is a highly volatile element and its abundance in meteorites may help better understand volatility-controlled processes in the solar nebula and on meteorite parent bodies. The large thermal neutron capture cross section of ¹¹³Cd suggests that Cd isotopes might be well suited to quantify neutron fluences in extraterrestrial materials. The aims of this study were (1) to evaluate the range and magnitude of Cd concentrations in magmatic iron meteorites, and (2) to assess the potential of Cd isotopes as a neutron dosimeter for iron meteorites. Our new Cd concentration data determined by isotope dilution demonstrate that Cd concentrations in iron meteorites are significantly lower than in some previous studies. In contrast to large systematic variations in the concentration of moderately volatile elements like Ga and Ge, there is neither systematic variation in Cd concentration amongst troilites, nor amongst metal phases of different iron meteorite groups. Instead, Cd is strongly depleted in all iron meteorite groups, implying that the parent bodies accreted well above the condensation temperature of Cd (i.e., ≈650 K) and thus incorporated only minimal amounts of highly volatile elements. No Cd isotope anomalies were found, whereas Pt and W isotope anomalies for the same iron meteorite samples indicate a significant fluence of epithermal and higher energetic neutrons. This observation demonstrates that owing to the high Fe concentrations in iron meteorites, neutron capture mainly occurs at epithermal and higher energies. The combined Cd-Pt-W isotope results from this study thus demonstrate that the relative magnitude of neutron capture-induced isotope anomalies is strongly affected by the chemical composition of the irradiated material. The resulting low fluence of thermal neutrons in iron meteorites and their very low Cd concentrations make Cd isotopes unsuitable as a neutron dosimeter for iron meteorites.

Reference
Kruijer TS, Sprung P, Kleine T, Leya I and Wieler R (in press) The abundance and isotopic composition of Cd in iron meteorites. Meteoritics & Planetary Science
[doi:10.1111/maps.12240]
Published by arrangement with John Wiley & Sons

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Maria Lugaro¹, Giuseppe Tagliente^2,8, Amanda I. Karakas³, Paolo M. Milazzo⁴, Franz Käppeler⁵, Andrew M. Davis^6,9,10, and Michael R. Savina^7,9

¹Monash Centre for Astrophysics (MoCA), Monash University, Clayton, VIC 3800, Australia
²Istituto Nazionale di Fisica Nucleare (INFN), Bari, Italy
³Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
⁴Istituto Nazionale di Fisica Nucleare (INFN), Trieste, Italy
⁵Karlsruhe Institute of Technology, Campus North, D-76021 Karlsruhe, Germany
⁶The Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637, USA
⁷Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
⁸Also at University of Ghent, Ghent, Belgium.
⁹Also at Chicago Center for Cosmochemistry, USA.
¹⁰Also at The Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA.

We present model predictions for the Zr isotopic ratios produced by slow neutron captures in C-rich asymptotic giant branch (AGB) stars of masses 1.25-4 M_☉ and metallicities Z = 0.01-0.03, and compare them to data from single meteoritic stardust silicon carbide (SiC) and high-density graphite grains that condensed in the outflows of these stars. We compare predictions produced using the Zr neutron-capture cross sections from Bao et al. and from n_TOF experiments at CERN, and present a new evaluation for the neutron-capture cross section of the unstable isotope ⁹⁵Zr, the branching point leading to the production of ⁹⁶Zr. The new cross sections generally present an improved match with the observational data, except for the ⁹²Zr/⁹⁴Zr ratios, which are on average still substantially higher than predicted. The ⁹⁶Zr/⁹⁴Zr ratios can be explained using our range of initial stellar masses, with the most ⁹⁶Zr-depleted grains originating from AGB stars of masses 1.8-3 M_☉ and the others from either lower or higher masses. The ^90,91Zr/⁹⁴Zr variations measured in the grains are well reproduced by the range of stellar metallicities considered here, which is the same needed to cover the Si composition of the grains produced by the chemical evolution of the Galaxy. The ⁹²Zr/⁹⁴Zr versus ²⁹Si/²⁸Si positive correlation observed in the available data suggests that stellar metallicity rather than rotation plays the major role in covering the ^90,91,92Zr/⁹⁴Zr spread.

Reference
Lugaro M, Tagliente G, Karakas AI, Milazzo PM, Käppeler F, Davis AM and Savina MR (2014) The Impact of Updated Zr Neutron-capture Cross Sections and New Asymptotic Giant Branch Models on Our Understanding of the S Process and the Origin of Stardust. The Astrophysical Journal 780:95.
[doi:10.1088/0004-637X/780/1/95]

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