Thomas F. Nägler¹, Ariel D. Anbar^2,3, Corey Archer⁴, Tatiana Goldberg⁵, Gwyneth W. Gordon², Nicolas D. Greber¹, Christopher Siebert⁶, Yoshiki Sohrin⁷, Derek Vance⁴

¹Institut für Geologie, Universität Bern, Bern, Switzerland
²School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
³Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ, USA
⁴Department of Earth Sciences, Institute of Geochemistry and Petrology, ETH Zürich, Zürich, Switzerland
⁵Department of Earth Science and Engineering, Imperial College London, London, UK
⁶Helmholtz Centre for Ocean Research, GEOMAR, Kiel, Germany
⁷Institute for Chemical Research, Kyoto University, Uji, Japan

Molybdenum isotopes are increasingly widely applied in Earth Sciences. They are primarily used to investigate the oxygenation of Earth’s ocean and atmosphere. However, more and more fields of application are being developed, such as magmatic and hydrothermal processes, planetary sciences or the tracking of environmental pollution. Here, we present a proposal for a unifying presentation of Mo isotope ratios in the studies of mass-dependent isotope fractionation. We suggest that the δ^98/95Mo of the NIST SRM 3134 be defined as +0.25‰. The rationale is that the vast majority of published data are presented relative to reference materials that are similar, but not identical, and that are all slightly lighter than NIST SRM 3134. Our proposed data presentation allows a direct first-order comparison of almost all old data with future work while referring to an international measurement standard. In particular, canonical δ^98/95Mo values such as +2.3‰ for seawater and −0.7‰ for marine Fe–Mn precipitates can be kept for discussion. As recent publications show that the ocean molybdenum isotope signature is homogeneous, the IAPSO ocean water standard or any other open ocean water sample is suggested as a secondary measurement standard, with a defined δ^98/95Mo value of +2.34 ± 0.10‰ (2s).

Reference
Nägler TF, Anbar AD, Archer C, Goldberg T, Gordon GW, Greber ND, Siebert C, Sohrin Y and Vance D (in press) Proposal for an International Molybdenum Isotope Measurement Standard and Data Representation. Geostandards and Geoanalytical Research
[doi:10.1111/j.1751-908X.2013.00275.x]
Published by arrangement with John Wiley & Sons

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Ai-Cheng Zhang^a,b, Shoichi Itoh^b,1, Naoya Sakamoto^c, Ru-Cheng Wang^a, Hisayoshi Yurimoto^b,c

^aState Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210046, China
^bDepartment of Natural History Sciences, Hokkaido University, Sapporo 060-0810, Japan
^cIsotope Imaging Laboratory, Creative Research Institution, Hokkaido University, Sapporo 001-0021, Japan
¹Division of Earth and Planetary Sciences, Kyoto University, Kyoto 606- 8502, Japan

Aluminum-rich chondrules are one of the most interesting components of primitive chondrites, because they have characteristics that are similar to both CAIs and ferromagnesian chondrules. However, their precursor and formation history remain poorly constrained, especially with respect to their oxygen isotopic distributions. In this study, we report on the petrography, mineralogy, oxygen isotope ratios, and rare-earth-element compositions of a sapphirine-bearing Al-rich chondrule (SARC) in the ungrouped chondrite Dar al Gani (DaG) 978. The SARC has a complex core-mantle-rim texture; while both the core and the mantle are mainly composed of Al-rich enstatite and anorthite with minor amounts of mesostasis, these regions are distinguished by the presence of Fe-rich spinel and sapphirine in the core and their absence in the mantle. The rim of the SARC consists mainly of Fe-rich olivine, enstatite, and Fe-Ni metal. Spinel and some olivine grains in the SARC are ¹⁶O-rich, with Δ¹⁷O values down to –20‰ and –23‰, respectively. Enstatite, sapphirine, and most olivine grains have similar Δ¹⁷O values (∼ –7‰), which are lower than those of anorthite and the mesostasis (including augite therein) (Δ¹⁷O: ∼ –3‰). Mesostasis from both the core and mantle have Group II rare-earth-element (REE) patterns; however, the core mesostasis has higher REE concentrations than the mantle mesostasis. These observations provide a strong indication that the SARC formed by the melting and crystallization of a mixture of materials from Group II Ca,Al-rich inclusions (CAIs) and ferromagnesian chondrules. Both spinel and olivine with ¹⁶O-rich features could be of relict origin. The ¹⁶O-poor isotopic compositions of most components in Al-rich chondrules can be explained by oxygen isotopic exchange between the melt and ¹⁶O-poor nebular gas (Δ¹⁷O: ∼ –7‰) during melting in chondrule-forming regions; whereas the anorthite and mesostasis could have experienced further oxygen isotopic exchange with a relatively ¹⁶O-poor reservoir (Δ¹⁷O: ∼ –3‰) on the parent body, likely during fluid-assisted thermal metamorphism. During the same thermal metamorphism event, spinel, olivine, some enstatite, and the mesostasis experienced Mg-Fe exchange to various extents.

Reference
Zhang A-C, Itoh S, Naoya Sakamoto N, Wang R-C and Hisayoshi Yurimoto H (in press) Origins of Al-rich chondrules: Clues from a compound Al-rich chondrule in the Dar al Gani 978 carbonaceous chondrite. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2013.12.026]
Copyright Elsevier

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

¹Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstr. 2, D-12489 Berlin, Germany

The near-Earth object (NEO) population, which mainly consists of fragments from collisions between asteroids in the main asteroid belt, is thought to include contributions from short-period comets as well. One of the most promising NEO candidates for a cometary origin is near-Earth asteroid (3552) Don Quixote, which has never been reported to show activity. Here we present the discovery of cometary activity in Don Quixote based on thermal-infrared observations made with the Spitzer Space Telescope in its 3.6 and 4.5 μm bands. Our observations clearly show the presence of a coma and a tail in the 4.5 μm but not in the 3.6 μm band, which is consistent with molecular band emission from CO₂. Thermal modeling of the combined photometric data on Don Quixote reveals a diameter of 18.4 km and an albedo of , which confirms Don Quixote to be the third-largest known NEO. We derive an upper limit on the dust production rate of 1.9 kg s^–1 and derive a CO₂ gas production rate of (1.1 ± 0.1) × 10²⁶ molecules s^–1. SpitzerInfrared Spectrograph spectroscopic observations indicate the presence of fine-grained silicates, perhaps pyroxene rich, on the surface of Don Quixote. Our discovery suggests that CO₂ can be present in near-Earth space over a long time. The presence of CO₂ might also explain that Don Quixote’s cometary nature remained hidden for nearly three decades.

Reference
Mommert et al. (2014) The Discovery of Cometary Activity in Near-Earth Asteroid (3552) Don Quixote. The Astrophysical Journal 781:25.
[doi:10.1088/0004-637X/781/1/25]

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L. J. Karssemeijer¹, S. Ioppolo^1,2, M. C. van Hemert³, A. van der Avoird¹, M. A. Allodi⁴, G. A. Blake^2,4 and H. M. Cuppen¹

¹Theoretical Chemistry, Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
²Division of Geological and Planetary Science, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
³Gorlaeus Laboratories, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands
⁴Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA

The long-timescale behavior of adsorbed carbon monoxide on the surface of amorphous water ice is studied under dense cloud conditions by means of off-lattice, on-the-fly, kinetic Monte Carlo simulations. It is found that the CO mobility is strongly influenced by the morphology of the ice substrate. Nanopores on the surface provide strong binding sites, which can effectively immobilize the adsorbates at low coverage. As the coverage increases, these strong binding sites are gradually occupied leaving a number of admolecules with the ability to diffuse over the surface. Binding energies and the energy barrier for diffusion are extracted for various coverages. Additionally, the mobility of CO is determined from isothermal desorption experiments. Reasonable agreement on the diffusivity of CO is found with the simulations. Analysis of the 2152 cm⁻¹ polar CO band supports the computational findings that the pores in the water ice provide the strongest binding sites and dominate diffusion at low temperatures.

Reference
Karssemeijer LJ, Ioppolo S, van Hemert MC, van der Avoird A, Allodi Ma, Blake GA and Cuppen HM (2014) Dynamics of CO in Amorphous Water-ice Environments. The Astrophysical Journal 781:16.
[doi:10.1088/0004-637X/781/1/16]

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Fara N. Lindsay^a, Gregory F. Herzog^a, Jisun Park^a,b, Jeremy S. Delaney^a, Brent Turrin^c, Carl C. Swisher III^c

^aDepartment of Chemistry and Chemical Biology Rutgers University 610 Taylor Rd. Piscataway, NJ 8854
^bLunar and Planetary Institute 3600 Bay Area Blvd. Houston, TX 77058
^cDepartment of Earth and Planetary Sciences Rutgers University 610 Taylor Rd. Piscataway, NJ 08854

⁴⁰Ar/³⁹Ar ages of single feldspar grains from the paired meteorites Graves Nunatak 06128 (GRA8; 8 grains) and 06129 (GRA9; 26 grains) are presented. Plateau ages (⩾70% of the ³⁹Ar released) ranged from 4000 Ma to 4600 Ma with an average 1-σ uncertainty of ± 90 Ma. The most precise ages obtained were 4267±17 Ma for a grain from GRA8 and 4437±19 Ma and 4321±18 Ma for two grains from GRA9. Isotope correlation diagrams yield less precise ages ranging from 3800 Ma to 5200 Ma with an average 1-σ uncertainty of 250 Ma; they indicate a negligible trapped component. Plateau ages, integrated total fusion ages, and isochron ages are internally concordant at the 95% confidence level.
The distribution of the plateau ages for GRA9 is bimodal with peaks at 4400 and 4300 Ma. In contrast, the plateau age distribution for GRA8 peaks at about 4260 Ma with broad wings extending toward younger and older ages. To explain the distributions of grain ages we prefer a scenario that includes a major post-formation event about 4400 Ma ago and a later melt intrusion event that heated GRA8 more than some parts of GRA9.

Reference
Lindsay FN, Herzog GF, Park J, Delaney JS, Turrin B and Swisher III CC (in press) 40Ar/39Ar dating of microgram feldspar grains from the paired feldspathic achondrites GRA 06128 and 06129. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2013.12.023]
Copyright Elsevier

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V. G. Shevchenko^1,2,*, I. G. Slyusarev¹, I. N. Belskaya¹

¹Astronomical Institute, Kharkiv V. N. Karazin National University, Kharkiv, Ukraine
²Department of Astronomy, Kharkiv V. N. Karazin National University, Kharkiv, Ukraine

CCD-photometry was performed for two Jupiter Trojan asteroids (911) Agamemnon and (4709) Ennomos for which the diameters were obtained from occultation events. New data on rotation periods, lightcurve amplitudes, color indices, magnitude–phase slopes, and absolute magnitudes were obtained for these asteroids. We have used the diameters from occultations (166 and 99 km) and new data on absolute magnitudes at the instant occultation (7.95 and 8.85 mag) to revise their albedos to 0.042 (911 Agamemnon) and 0.052 (4709 Ennomos).

Reference
Shevchenko VG, Slyusarev IG and Belskaya IN (in press) Revised albedos of Trojan asteroids (911) Agamemnon and (4709) Ennomos. Meteoritics & Planetary Science
[doi:10.1111/maps.12234]
Published by arrangement with John Wiley & Sons

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