¹Fang, C.M., ¹Van Huis, M.A., ²Sluiter, M.H.F. 
¹Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 5, Utrecht, Netherlands
²Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, Delft, Netherlands

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Reference
Fang CM, Van Huis MA, Sluiter MHF (2015) Formation, structure and magnetism of the γ-(Fe,M)23C6 (M = Cr, Ni) phases: A first-principles study. Acta Materialia 103, 273-279
Link to Article [DOI: 10.1016/j.actamat.2015.08.078]

¹J.F. Snape, ^1,2A.A. Nemchin, ²M.L. Grange, ¹J.J. Bellucci, ¹F. Thiessen, ¹M.J. Whitehouse
¹Department of Geosciences, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden
²Department of Applied Geology, Curtin University, Perth, WA 6845, Australia

The U-Pb systems of apatite and merrillite grains within four separate Apollo 14 impact melt breccia samples were analysed by secondary ion mass spectrometry. No systematic difference was identified between the 207Pb/206Pb ages of the apatites and merrillites. A combined 207Pb/206Pb age of 3927±2 Ma (95% conf.) is determined for three of these samples (14305,103: 3926±4 Ma; 14306,150: 3926±6 Ma; 14314,13: 3929±4 Ma). By combining these data with the ages previously obtained for zircons in Apollo 12 impact melt breccia fragments and the lunar meteorite SaU 169, a weighted average age of 3926±2 Ma (95% conf.) is obtained, which is attributed to the formation of the Imbrium basin. An age of 3943±5 Ma is determined for the fourth breccia (14321,134), which is similar to ages of 3946±15 Ma and 3958±19 Ma, obtained from several older phosphates in 14305,103 and 14314,13. The weighted average of these three older ages is 3944±4 Ma (95% conf.). This is indistinguishable to the age (3938±4 Ma; 2σ) obtained for a different Apollo 14 impact melt breccia in a previous study. After investigating likely sources for this older ∼3940 Ma age, we conclude that the Humorum or Serenitatis basin forming events are likely candidates. The potential identification of two large impact events within ∼15 Myrs has important implications for the rate of lunar bombardment around 3.95-3.92 Ga. This study demonstrates the importance of high-precision age determinations for interpreting the impact record of the Moon, as documented in lunar samples.

Reference
Snape SF, Nemchin AA, Grange ML, Bellucci JJ, Thiessen F, Whitehouse MJ (2015) Phosphate ages in Apollo 14 breccias: Resolving multiple impact events with high precision U-Pb SIMS analyses. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.11.005]
Copyright Elsevier

^1,2K.R. Bermingham, ^1,3K. Mezger, ¹E.E. Scherer, ⁴M. Horan, ⁴R. Carlson, ^1,5D. Upadhyay, ^1,6T. Magna,⁷A. Pack
¹Institut für Mineralogie, Westfälische Wilhelms-Universität, Corrensstraße 24, 48149 Münster, Germany
²Isotope Geochemistry Laboratory, Department of Geology, University of Maryland, College Park, MD-20740 USA
³Institut für Geologie, Universität Bern, Baltzerstrasse 1 + 3, 3012 Bern, Switzerland
⁴Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Road NW, Washington DC 20015 USA
⁵Department of Geology and Geophysics, Indian Institute of Technology Kharagpur, 721302, Kharagpur, India
⁶Czech Geological Survey, Klárov 3, 11821 Prague 1, Czech Republic
⁷Geowissenschaftliches Zentrum, Georg-August-Universität, Goldschmidtstraße 1, 37077 Göttingen, Germany

Several nucleosynthetic processes contributed material to the Solar System; however, the relative contributions of each process, the timing of their input into the solar nebula, and how well these components were homogenized in the solar nebula remain only partially constrained. The Ba isotope system is particularly useful in addressing these issues because Ba contains isotopes are synthesized through three nucleosynthetic processes (s-, r-, p-process). In this study, high precision Ba isotope analyses of 22 different whole rock chondrites and achondrites (carbonaceous chondrites, ordinary chondrites, enstatite chondrites, Martian meteorites, and eucrites) were performed to constrain the distribution of Ba isotopes on the regional scale in the Solar System. A melting method using aerodynamic levitation and CO2-laser heating was used to oxidize SiC, a primary carrier of Ba among presolar grains in carbonaceous chondrites. Destruction of these grains during the fusion process enabled the complete digestion of these samples. The Ba isotope data presented here are thus the first for which complete dissolution of the bulk meteorite samples was certain. Enstatite chondrites, ordinary chondrites, and all achondrites measured here possess Ba isotope compositions that are not resolved from the terrestrial Ba isotope composition. Barium isotope anomalies are evident in most of the carbonaceous chondrites analyzed, but the 135Ba anomalies are generally smaller than previously reported for similarly sized splits of CM2 meteorites. Variation in the size of the 135Ba anomaly is also apparent in fused samples from the same parent body (e.g., CM2 meteorites) and in different pieces from the same meteorite (e.g., Orgueil, CI). Here, we investigate the potential causes of variability in 135Ba, including the contribution of radiogenic 135Ba from the decay of 135Cs and incomplete homogenization of the presolar components on the

Reference
Bermingham KR,Mezger K,Scherer EE, Horan M,Carlson R, Upadhyay D, Magna T,Pack A (2015) Barium Isotope Abundances in Meteorites and Their Implications for Early Solar System Evolution. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.11.006]

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¹D. J. Wilson, ¹B. T. Gänsicke, ²D. Koester, ¹O. Toloza, ¹A. F. Pala, ¹E. Breedt,³S. G. Parsons
¹Department of Physics, University of Warwick, Coventry CV4 7AL, UK
²Institut für Theoretische Physik und Astrophysik, University of Kiel, D-24098 Kiel, Germany
³Departamento de Física y Astronomía, Universidad de Valparaíso, Avenida Gran Bretaña 1111, Valparaíso 2360102, Chile

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Reference
Wilson DJ, Gänsicke BT, Koester D, Toloza O, Pala AF, Breedt E, Parsons SG (2015) The composition of a disrupted extrasolar planetesimal at SDSS J0845+2257 (Ton 345). Monthly Notices of the Royal Astronomical Society 451, 3237-3248.
Link to Article [doi: 10.1093/mnras/stv1201]

^1,2,6Lydia J. Hallis, ^1,2Gary R. Huss, ²Kazuhide Nagashima, ^1,2G. Jeffrey Taylor, ³Sæmundur A. Halldórsson, ³David R. Hilton, ⁴Michael J. Mottl, ^1,5Karen J. Meech
¹NASA Astrobiology Institute, Institute for Astronomy, University of Hawai’i, 2680 Woodlawn Drive, Honolulu, HI 96822-1839, USA.
²Hawai’i Institute of Geophysics and Planetology, Pacific Ocean Science and Technology (POST) Building, University of Hawai’i, 1680 East-West Road, Honolulu, HI 96822, USA.
³Scripps Institution of Oceanography, University California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0244, USA.
⁴Department of Oceanography, University of Hawai’i, Marine Sciences Building 304, 1000 Pope Road, Honolulu, HI 96822, USA.
⁵Institute for Astronomy, University of Hawai’i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA.
⁶School of Geographical and Earth Sciences, University of Glasgow, Gregory Building, Lillybank Gardens, Glasgow G12 8QQ, UK.

The hydrogen-isotope [deuterium/hydrogen (D/H)] ratio of Earth can be used to constrain the origin of its water. However, the most accessible reservoir, Earth’s oceans, may no longer represent the original (primordial) D/H ratio, owing to changes caused by water cycling between the surface and the interior. Thus, a reservoir completely isolated from surface processes is required to define Earth’s original D/H signature. Here we present data for Baffin Island and Icelandic lavas, which suggest that the deep mantle has a low D/H ratio (δD more negative than –218 per mil). Such strongly negative values indicate the existence of a component within Earth’s interior that inherited its D/H ratio directly from the protosolar nebula.

Reference
Hallis LJ, Huss GR, Nagashima K, Taylor GJ, Halldórsson SA, Hilton DR, Mottl MJ, Meech KJ (2015)Evidence for primordial water in Earth’s deep mantle. Science 350, 795-797.
Link to Article [DOI: 10.1126/science.aac4834]
Reprinted with permission by AAAS

¹N. van der Marel, ¹P. Pinilla, ^1,3J. Tobin, ¹T. van Kempen, ²S. Andrews, ²L. Ricci, ²T. Birnstiel
¹Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, The Netherlands
²Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
³VENI fellow.

Azimuthally asymmetric dust distributions observed with the Atacama Large Millimeter/submillimeter Array (ALMA) in transition disks have been interpreted as dust traps. We present Very Large Array Ka band (34 GHz or 0.9 cm) and ALMA Cycle 2 Band 9 (680 GHz or 0.45 mm) observations at a 0farcs2 resolution of the Oph IRS 48 disk, which suggest that larger particles could be more azimuthally concentrated than smaller dust grains, assuming an axisymmetric temperature field or optically thin 680 GHz emission. Fitting an intensity model to both data demonstrates that the azimuthal extent of the millimeter emission is 2.3 ± 0.9 times as wide as the centimeter emission, marginally consistent with the particle trapping mechanism under the above assumptions. The 34 GHz continuum image also reveals evidence for ionized gas emission from the star. Both the morphology and the spectral index variations are consistent with an increase of large particles in the center of the trap, but uncertainties remain due to the continuum optical depth at 680 GHz. Particle trapping has been proposed in planet formation models to allow dust particles to grow beyond millimeter sizes in the outer regions of protoplanetary disks. The new observations in the Oph IRS 48 disk provide support for the dust trapping mechanism for centimeter-sized grains, although additional data are required for definitive confirmation.

Reference
van der Marel N, Pinilla P, Tobin J, van Kempen T, Andrews S, L. Ricci2, Birnstiel T (2015) A CONCENTRATION OF CENTIMETER-SIZED GRAINS IN THE OPHIUCHUS IRS 48 DUST TRAP. Astrophysical Journal Letters 810, L7
Link to Article [http://dx.doi.org/10.1088/2041-8205/810/1/L7]

^1,2Matthieu Gounelle
¹IMPMC, Muséum National d’Histoire Naturelle, Sorbonne Universités, CNRS, UPMC & IRD, 57 rue Cuvier, 75005 Paris, France
e-mail: gounelle@mnhn.fr
²Institut Universitaire de France, 103 boulevard Saint-Michel, 75005 Paris, France

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Reference
Gounelle M et al. (2015) The abundance of 26Al-rich planetary systems in the Galaxy. Astronomy & Astrophysics 582, A26
Link to Article [http://dx.doi.org/10.1051/0004-6361/201526174]

¹Povinec, P.P., ¹Sýkora, I., ¹Kováčik, A., ^2,3Koeberl, C.
¹Department of Nuclear Physics and Biophysics, Faculty of Mathematics, Physics and Informatics, Comenius University, Mlynská dolina F-1, Bratislava, Slovakia
²Natural History Museum, Burgring 7, Vienna, Austria
³Department of Lithospheric Research, University of Vienna, Vienna, Austria

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Reference
Povinec PP, Sýkora I, Kováčik A, Koeberl C (2015) High-sensitivity HPGe gamma-spectrometry analysis of radionuclides in Martian meteorites. Journal of Radioanalytical and Nuclear Chemistry (in Press)
Link to Article [DOI: 10.1007/s10967-015-4523-5]

¹Josh Wimpenny, ²Yuri Amelin, ¹Qing-zhu Yin
¹Department of Earth and Planetary Sciences, University of California, One Shields Avenue, Davis, CA 95616, USA
²Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia

Studies of Lu–Hf isotope systematics in meteorites have produced apparent “ages” that are older than Pb–Pb ages and older than the estimated age of our solar system. One proposed explanation for this discrepancy is that irradiation by cosmic rays caused excitation of 176Lu to its short-lived isomer that then underwent rapid decay to 176Hf. This explanation can account for apparent excesses in 176Hf that correlate with Lu/Hf ratio. Mass balance requires that samples with measurable excess in 176Hf should also have measurable deficiencies in 176Lu on the order of 1‰–3‰. To unambiguously test the accelerated decay hypothesis, we have measured the 176Lu/175Lu ratio in terrestrial materials and achondrites to search for evidence of depletion in 176Lu. To a precision of 0.1‰ terrestrial standards, cumulate and basaltic eucrites and angrites all have the same 176Lu/175Lu ratio. Barring a subsequent mass-dependent fractionation event, these results suggest that the apparent excesses in 176Hf are not caused by accelerated decay of 176Lu, and so another hypothesis is required to explain apparently old Lu–Hf ages.

Reference
Wimpenny J, Amelin Y, Y Qing-zhu Yin (2015) THE LU ISOTOPIC COMPOSITION OF ACHONDRITES: CLOSING THE CASE FOR ACCELERATED DECAY OF 176LU. Astrophysical Journal Letters 812, L3
Link to Article [http://dx.doi.org/10.1088/2041-8205/812/1/L3]

¹F.J.M. Rietmeijer, ²V. Della Corte, ²M. Ferrari, ^2,3A. Rotundi, ⁴R. Brunetto
¹Department of Earth and Planetary Sciences, MSC03 2040, 1-University of New Mexico, Albuquerque, NM 87131-0001, USA
²Istituto di Astrofisica e Planetologia Spaziali – INAF, Via del Fosso del Cavaliere, 100, 00133, Roma, Italy
³Dipartimento di Scienze Applicate, Università degli Studi di Napoli “Parthenope”, CDN, I C4, 80143, Napoli, Italy
⁴Institut d’Astrophysique Spatiale, CNRS, UMR-8617, Université Paris-Sud, bâtiment 121, F-91405 Orsay Cedex, France

Bolide and fireball fragmentation produce vast amounts of dust that will slowly fall through the stratosphere. DUSTER (Dust in the Upper Stratosphere Tracking Experiment and Retrieval) was designed to intercept the nanometer to micrometer meteoric dust from these events for laboratory analyses while it is still in the upper stratosphere. This effort required extraordinary precautions to avoid particle contamination during collection and in the laboratory. Here we report dust from the upper stratosphere that was collected during two campaigns one in 2008 and another in 2011. We collected and characterized forty five uncontaminated meteoric dust particles. The collected particles are alumina, aluminosilica, plagioclase, fassaite, silica, CaCO3, CaO, extreme F-rich C-O-Ca particles, and oxocarbon particles. These particles are found in friable CI and CM carbonaceous chondrite, and unequilibrated ordinary chondrite meteoroids that are the most common source of bolides and fireballs. The oxocarbons have no meteorite counterparts. Some F-bearing CaCO3 particles changed shape when they interacted with the ambient laboratory atmosphere which might indicate their highly unequilibrated state as a result of fragmentation. Equilibrium considerations constrain the thermal regime experienced by the collected particles between ∼2000°C and ∼1000°C, as high as 3,700°C and as low as ∼650°C after 9 secs, followed by rapid quenching (μs) to below 1,600°C, but equilibrium conditions during these events is most unlikely. So far the observed thermal conditions in these events put the temperatures between ∼4,300°C and ∼430°C for 5 seconds and high cooling rates. Such conditions are present in the immediate wake of meteors and fireballs.

Reference
Rietmeijer FJM, Della Corte V, Ferrari M, Rotundi A, Brunetto R (2015) Laboratory Analyses of Meteoric Debris in the Upper stratosphere from Settling Bolide Dust Clouds. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.11.003]
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