D.J. Cherniak^a and J.A. Van Orman^b

^aDepartment of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180, USA
^bDepartment of Earth, Environmental and Planetary Sciences, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, USA

Diffusion of tungsten has been characterized in synthetic forsterite and natural olivine (Fo₉₀) under dry conditions. The source of diffusant was a mixture of magnesium tungstate and olivine powders. Experiments were prepared by sealing the source material and polished olivine under vacuum in silica glass ampoules with solid buffers to buffer at NNO or IW. Prepared capsules were annealed in 1 atm furnaces for times ranging from 45 minutes to several weeks, at temperatures from 1050 to 1450°C. Tungsten distributions in the olivine were profiled by Rutherford Backscattering Spectrometry (RBS).
The following Arrhenius relation is obtained for W diffusion in forsterite:
D_W=1.0×10-8exp(-365±28kJ mol^-1/RT)m²sec^-1
Diffusivities for the synthetic forsterite and natural Fe-bearing olivine are similar, and tungsten diffusion in olivine shows little dependence on crystallographic orientation or oxygen fugacity.
The slow diffusivities measured for W in olivine indicate that Hf-W ages in olivine-metal systems will close to diffusive exchange at higher temperatures than other chronometers commonly used in cosmochronology, and that tungsten isotopic signatures will be less likely to be reset by subsequent thermal events.

Reference
Cherniak DJ and Van Orman JA (in press) Tungsten Diffusion in Olivine. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2013.12.020]
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E. Bowell¹, D. A. Oszkiewicz^2,3,*, L. H. Wasserman¹, K. Muinonen^2,4, A. Penttilä², D. E. Trilling⁵

¹Lowell Observatory, Flagstaff, Arizona, USA
²Department of Physics, University of Helsinki, Helsinki, Finland
³Institute Astronomical Observatory, Faculty of Physics, Adam Mickiewicz University, Poznań, Poland
⁴Finnish Geodetic Institute, Masala, Finland

By analyzing brightness variation with ecliptic longitude and using the Lowell Observatory photometric database, we estimate spin-axis longitudes for more than 350,000 asteroids. Hitherto, spin-axis longitude estimates have been made for fewer than 200 asteroids. We investigate longitude distributions in different dynamical groups and asteroid families. We show that asteroid spin-axis longitudes are not isotropically distributed as previously considered. We find that the spin-axis longitude distribution for Main Belt asteroids is clearly nonrandom, with an excess of longitudes from the interval 30°–110° and a paucity between 120° and 180°. The explanation of the nonisotropic distribution is unknown at this point. Further studies have to be conducted to determine if the shape of the distribution can be explained by observational bias, selection effects, a real physical process, or other mechanism.

Reference
Bowell E, Oszkiewicz DA, Wasserman LH, Muinonen K, Penttilä A and Trilling DE (in press) Asteroid spin-axis longitudes from the Lowell Observatory database. Meteoritics & Planetary Science
[doi:10.1111/maps.12230]
Published by arrangement with John Wiley & Sons

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Joshua L. Bandfield^a, Eugenie Song^b, Paul O. Hayne^c, Brittany D. Brand^d, Rebecca R. Ghent^e, Ashwin R. Vasavada^c, David A. Paige^f

^aSpace Science Institute
^bHawai’i Institute of Geophysics and Planetology, University of Hawai’i
^cJet Propulsion Laboratory, California Institute of Technology
^dDepartment of Geosciences, Boise State University
^eDepartment of Geology, University of Toronto
^fEarth and Space Sciences, UCLA

Systematic temperature mapping and high resolution images reveal a previously unrecognized class of small, fresh lunar craters. These craters are distinguished by near-crater deposits with evidence for lateral, ground-hugging transport. More distal, highly insulating surfaces surround these craters and do not show evidence of either significant deposition of new material or erosion of the substrate. The near-crater deposits can be explained by a laterally propagating granular flow created by impact in the lunar vacuum environment. Further from the source crater, at distances of ∼10–100 crater radii, the upper few to 10’s of centimeters of regolith appear to have been “fluffed-up” without the accumulation of significant ejecta material. These properties appear to be common to all impacts, but quickly degrade in the lunar space weathering environment. Cratering in the vacuum environment involves a previously unrecognized set of processes that leave prominent, but ephemeral, features on the lunar surface.

Reference
Bandfield JL, Song E, Hayne PO, Brand BD, Ghent RR, Vasavad AR and Paige DA (in press) Lunar cold spots: Granular flow features and extensive insulating materials surrounding young craters. Icarus
[doi:10.1016/j.icarus.2013.12.017]
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James F.J. Bryson^a, Nathan S. Church^a, Takeshi Kasama^b, Richard J. Harrison^a

^aDepartment of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
^bCenter for Electron Nanoscopy, Technical University of Denmark, Kongens Lyngby, Denmark

Nanoscale intergrowths unique to the cloudy zones (CZs) of meteoritic metal display novel magnetic behaviour with the potential to reveal new insight into the early development of magnetic fields on protoplanetary bodies. The nanomagnetic state of the CZ within the Tazewell IIICD iron meteorite has been imaged using off-axis electron holography. The CZ is revealed to be a natural nanocomposite of magnetically hard islands of tetrataenite (ordered FeNi) embedded in a magnetically soft matrix of ordered Fe₃Ni. In the remanent state, each tetrataenite island acts as a uniaxial single domain particle with its [001] magnetic easy axis oriented along one of three 〈100〉 crystallographic directions of the parent taenite phase. Micromagnetic simulations demonstrate that switching occurs via the nucleation and propagation of domain walls through individual tetrataenite particles. The switching field (H_s) varies with the length scale of the matrix phase (L_m), with H_s > 1 T for L_m ∼10 nm (approaching the intrinsic switching field for isolated single domain tetrataenite) and 0.2<H_s<0.6 T for L_m ∼30 nm. The reduction in H_s with increasing L_c is caused by exchange coupling between the hard tetrataenite islands and the soft magnetic matrix, which lowers the critical field for domain wall nucleation, providing an explanation for previously observed coercivity variations throughout the CZ. Non-random distributions of the tetrataenite easy axes are observed locally throughout the CZ, suggesting a magnetic field could have been present during nanostructure formation. This observation demonstrates the potential for stable chemical transformation remanent magnetisation to be encoded by the nanostructure, with variations in the proportions of the six possible magnetisation states reflecting the intensity and relative direction of the magnetic fields present during cooling. According to recent cooling models, the cooling rate of meteoritic metal originating near the surface of differentiated planetesimals was such that the magnetic signal across the CZ could potentially record dynamo field intensity and direction variations over time (10–100 Ma), which would enable events such as magnetic reversals and the decay of an asteroid dynamo to be observed.

Reference
Bryson JFJ, Church NS, Kasama T and Harrison RJ (2014) Nanomagnetic intergrowths in Fe–Ni meteoritic metal: The potential for time-resolved records of planetesimal dynamo fields. Earth and Planetary Science Letters 388:237–248.
[doi:10.1016/j.epsl.2013.12.004]
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K.R. Bermingham^a,b, K. Mezger^a,c, S.J. Desch^d, E.E. Scherer^a, M. Horstmann^e

^aInstitut für Mineralogie, Westfälische Wilhelms-Universität, Corrensstraße 24, Münster, 48149, Germany
^bIsotope Geochemistry Laboratory, Department of Geology, University of Maryland, College Park, MD-20742 USA
^cInstitut für Geologie, Universität Bern, Baltzerstrasse 1 + 3, 3012 Bern, Switzerland
^dSchool of Earth and Space Exploration, Arizona State University, P.O. Box 871404, Tempe, AZ-85287-1404 USA
^eInstitut für Planetologie, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Straße 10, Münster, 48149, Germany

The abundance and distribution of isotopes throughout the Solar System can be used to constrain the number and type of nucleosynthetic events that contributed material to the early nebula. Barium is particularly well suited to quantifying the degree of isotope heterogeneity in the Solar System because it comprises seven stable isotopes that were synthesized by three different nucleosynthetic processes (s-, r-, and p-processes), all of which contributed material to the Solar System. There is also potential contribution to ¹³⁵Ba from short-lived radioisotope ¹³⁵Cs, conclusive evidence for which is yet to be reported. Four Allende (CV3) Ca,Al-rich inclusions (CAI 1, CAI 2, CAI 4, CAI 5) and one Allende dark inclusion (DI) were analyzed for Ba isotope variability. Two CAIs (CAI 2 and CAI 5) display ¹³⁵Ba excesses that are not accompanied by ¹³⁷Ba anomalies. Calcium-aluminium-rich inclusion 1 displays a ¹³⁵Ba excess that is possibly coupled with a ¹³⁷Ba excess, and the remaining refractory inclusions (CAI 2 and DI) have terrestrial Ba isotope compositions. These Ba isotope data are presented in conjunction with published whole rock Ba isotope data from individual Allende CAIs. The enrichment in ¹³⁵Ba and absence of coupled ¹³⁷Ba excesses in CAI 2 and CAI 5 is interpreted to indicate that the anomalies are not purely nucleosynthetic in origin but also contain contributions (16 – 48 ppm) from the decay of short-lived ¹³⁵Cs. The majority of Allende CAIs studied to date may also have similar contributions from ¹³⁵Cs on the basis of higher than expected ¹³⁵Ba excesses if the Ba isotope anomalies were purely nucleosynthetic in origin. The ¹³⁵Ba anomalies appear not to be coupled with superchondritic Cs/Ba, which may imply that the contribution to ¹³⁵Ba did not occur via in situ decay of live ¹³⁵Cs. However, it is feasible that the CAIs had a superchondritic Cs/Ba during decay of ¹³⁵Cs, but Cs was subsequently removed from the system during aqueous alteration on the parent body. An alternative scenario is the potential existence of a transient high-temperature reservoir having superchondritic Cs/Ba in the early Solar System while ¹³⁵Cs was extant, which enabled a radiogenic ¹³⁵Ba signature to develop in some early condensates. The nucleosynthetic source of ¹³⁵Cs can be determined by reconciling the predicted astrophysical ¹³⁵Cs abundance with its measured abundance in meteorites. The currently accepted initial¹³⁵Cs/¹³³Cs of the Solar System, [¹³⁵Cs/¹³³Cs]₀, may be underestimated because the spread of Cs/Ba among samples is small and the range of excess ¹³⁵Ba is limited thus leading to inaccuracies when estimating [¹³⁵Cs/¹³³Cs]₀. If the initial meteoritic abundance of ¹³⁵Cs was indeed higher than is currently thought, the most probable stellar source of short-lived radioisotopes was a nearby core-collapse supernova and/or the Wolf-Rayet wind driven by its progenitor.

Reference
Bermingham KR, Mezger K, Desch SJ, Scherer EE and Horstmann M (in press) Evidence for extinct 135Cs from Ba isotopes in Allende CAIs? Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2013.12.016]
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A. Morlok^a,b, C. Lisse^c, A.B. Mason^d, E. Bullock^e, M.M. Grady^a,f

^aDepartment of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, UK
^bCurrent address: Institut für Planetologie, WWU Münster, Wilhelm-Klemm-Straße 10, 48149, Münster, Germany
^cThe Johns Hopkins University Applied Physics Laboratory,11100 Johns Hopkins Road, Laurel, MD 20723, USA
^dFinnish Centre for Astronomy with ESO (FINCA), University of Turku, Tuorla Observatory, Väisäläntie 20, FI-21500 PIIKKIÖ, Finland
^eSmithsonian Institution PO Box 37012, MRC 119 Washington, DC 20013-7012, USA
^fDepartment of Physical Sciences, The Open University, Walton Hall, MK7 6AA Milton Keynes, UK

We obtained mid-infrared spectra of chondrules, matrix, CAIs and bulk material from primitive type 1-4 chondrites in order to compare them with the dust material in young, forming solar systems and around comets. Our aim is to investigate whether there are similarities between the first processed materials in our early Solar System and protoplanetary disks currently forming around other stars. Chondrule spectra can be divided into two groups. 1) Chondrules dominated by olivine features at ∼11.3 μm and ∼10.0 μm. 2) mesostasis rich chondrules that show main features at ∼10 μm. Bulk ordinary chondrites show similar features to both groups.
Fine-grained matrix is divided into three groups. 1) phyllosilicate-rich with a main band at ∼10μm, 2) olivine-rich with bands at 11.3 μm and ∼10 μm, 3) pyroxene–rich with several peaks between 9.3 μm and 11.2 μm. Impact shock processed matrix from Murchison (CM2) shows features from phyllosilicate-rich, amorphous and olivine–rich material. CAIs show melilite/spinel –rich features between 10.2 μm and 12.5 μm.
Astronomical spectra are divided into four groups based on their spectral characteristics – amorphous (group 1), pyroxene-rich (group 2), olivine–rich (group 3) and ‘complex’ (group 4). Group 2 is similar to enstatite-rich fine grained material like e.g. Kakangari (K3) matrix. Group 3 and 4 can be explained by a combination of varying concentrations of olivine and mesostasis-rich chondrules and fine-grained matrix, but also show very good agreement with shock processed material. Comparison of band ratios confirms the similarity with chondritic material e.g. for HD100546, while the inner disk of HD142527 show no sign of chondrule material.
Comparison between the laboratory infrared-red IR data and astronomical spectra indicate a general similarity between primitive solar system materials and circumstellar dust and comets, especially in the inner disks of young solar systems. However, other amorphous materials like IDP/GEMS have to be taken into account.

Reference
Morlok A, Liss C, Mason AB, Bullock E and Grady MM (in press) Mid-Infrared Spectroscopy of Components in Chondrites: Search for Processed Materials in Young Solar Systems and Comets. Icarus
[doi:10.1016/j.gca.2013.12.020]
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Edward R. D. Scott

Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Manoa, Honolulu, HI, USA

This is an announcement without abstract.

Reference
Scott ERD (in press) Handbook of Iron Meteorites by Vagn F. Buchwald, 1975: Electronic edition. Meteoritics & Planetary Science 48:2608.
[doi:10.1111/maps.12232]
Published by arrangement with John Wiley & Sons

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Heng Chen¹, Bach Mai Nguyen¹ and Frédéric Moynier^1,2,*

¹Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, St. Louis, Missouri, USA
²Institut de Physique du Globe de Paris, Université Paris Diderot, Paris, France

High-precision Zn isotopic compositions measured by MC-ICP-MS are documented for 32 iron meteorites from various fractionally crystallized and silicate-bearing groups. The δ⁶⁶Zn values range from −0.59‰ up to +5.61‰ with most samples being slightly enriched in the heavier isotopes compared with carbonaceous chondrites (0 < δ⁶⁶Zn < 0.5). The δ⁶⁶Zn versus δ⁶⁸Zn plot of all samples defines a common linear fractionation line, which supports the hypothesis that Zn was derived from a single reservoir or from multiple reservoirs linked by mass-dependent fractionation processes. Our data for Redfields fall on a mass fractionation line and therefore refute a previous claim of it having an anomalous isotopic composition due to nonmixing of nucleosynthetic products. The negative correlation between δ⁶⁶Zn and the Zn concentration of IAB and IIE is consistent with mass-dependent isotopic fractionation due to evaporation with preferential loss of lighter isotopes in the vapor phase. Data for the Zn concentrations and isotopic compositions of two IVA samples demonstrate that volatile depletion in the IVA parent body is not likely the result of evaporation. This is important evidence that favors the incomplete condensation origin for the volatile depletion of the IVA parent body.

Reference
Chen H, Nguyen BM and Moynier F (2013) Zinc isotopic composition of iron meteorites: Absence of isotopic anomalies and origin of the volatile element depletion. Meteoritics & Planetary Science 48:2441–2450.
[doi:10.1111/maps.12229]
Published by arrangement with John Wiley & Sons

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Michail I. Petaev^a,b, Shichun Huang^a, Stein B. Jacobsen^a and Alan Zindler^a

^aDepartment of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138; and
^bSolar, Stellar, and Planetary Sciences, Harvard–Smithsonian Center for Astrophysics, Cambridge, MA 02138

Besides providing additional arguments against the Pt depositing event (1) as a cause of the Younger Dryas cooling, Boslough’s letter (2) raises an important question about the scale of this event. Indeed, a localized deposition of Pt by the Cape York meteorite shower is an attractive hypothesis considered by us initially (3), but abandoned because of (i) a large difference in the …

Reference
Petaev MI, Huang S, Jacobsen SB and Zindler A (2013) Reply to Boslough: Is Greenland Pt anomaly global or local?. PNAS 110:E5036.
[doi:10.1073/pnas.1320772111]

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Mark Boslough

Sandia National Laboratories, Albuquerque, NM 87185

Petaev et al. (1) tested the suite of hypotheses (collectively known as the “impact hypothesis”) that a swarm of impacts or airbursts from comets, chondritic, or stony asteroids caused an abrupt climate change, continental-scale wildfires, mass extinctions, and collapse of the Clovis culture at or near the Younger Dryas Boundary (YDB). The authors identify a large Pt anomaly in the Greenland Ice Sheet Project 2 (GISP2) core and suggest that it hints at an extraterrestrial source. Because there is no corresponding Ir spike, Petaev et al. challenge the impact hypothesis by proposing a highly fractionated iron meteorite. The Pt anomaly predates ammonimum and nitrate peaks in the GISP2 core by decades, eliminating …

Reference
Boslough M (2013) Greenland Pt anomaly may point to noncataclysmic Cape York meteorite entry. PNAS 110:E5035.
[doi:10.1073/pnas.1320328111]

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