Gregor J. Golabek^1,2, Bernard Bourdon² and Taras V. Gerya¹

¹ETH Zurich, Institute of Geophysics, Zurich, Switzerland
²Laboratoire de Géologie de Lyon, ENS Lyon, CNRS and Université Claude Bernard de Lyon, Lyon Cedex 07, France

The acapulcoite-lodranite meteorites are members of the primitive achondrite class. The observation of partial melting and resulting partial removal of Fe-FeS indicates that this meteorite group could be an important link between achondrite and iron meteorites, on the one hand, and chondrite meteorites, on the other. Thus, a better understanding of the thermomechanical evolution of the parent body of this meteorite group can help improve our understanding of the evolution of early planetesimals. Here, we use 2-D and 3-D finite-difference numerical models to determine the formation time, initial radius of the parent body of the acapulcoite-lodranite meteorites, and their formation depth inside the body by applying available geochronological, thermal, and textural constraints to our numerical data. Our results indicate that the best fit to the data can be obtained for a parent body with 25–65 km radius, which formed around 1.3 Ma after calcium-aluminum-rich inclusions. The 2-D and 3-D results considering various initial temperatures and the effect of porosity indicate possible formation depths of the acapulcoite-lodranite meteorites of 9–19 and 14–25 km, respectively. Our data also suggest that other meteorite classes could form at different depths inside the same parent body, supporting recently proposed models (Elkins-Tanton et al. 2011; Weiss and Elkins-Tanton2013).

Reference
Golabek GJ, Bourdon B and Gerya TV (in press) Numerical models of the thermomechanical evolution of planetesimals: Application to the acapulcoite-lodranite parent body. Meteoritics & Planetary Science
[doi:10.1111/maps.12302]
Published by arrangement with John Wiley & Sons

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Steven J. Jaret^1,†, Linda C. Kah¹ and R. Scott Harris^2,3

¹Department of Earth & Planetary Sciences, University of Tennessee, Knoxville, Tennessee, USA
²Department of Geological Sciences, Brown University, Providence, Rhode Island, USA
³Georgia Department of Transportation, Office of Materials and Testing, Forest Park, Georgia, USA
^††Department of Geosciences, Stony Brook University, Stony Brook, New York, USA

The Tenoumer impact structure is a small, well-preserved crater within Archean to Paleoproterozoic amphibolite, gneiss, and granite of the Reguibat Shield, north-central Mauritania. The structure is surrounded by a thin ejecta blanket of crystalline blocks (granitic gneiss, granite, and amphibolite) and impact-melt rocks. Evidence of shock metamorphism of quartz, most notably planar deformation features (PDFs), occurs exclusively in granitic clasts entrained within small bodies of polymict, glass-rich breccia. Impact-related deformation features in oligoclase and microcline grains, on the other hand, occur both within clasts in melt-breccia deposits, where they co-occur with quartz PDFs, and also within melt-free crystalline ejecta, in the absence of co-occurring quartz PDFs. Feldspar deformation features include multiple orientations of PDFs, enhanced optical relief of grain components, selective disordering of alternate twins, inclined lamellae within alternate twins, and combinations of these individual textures. The distribution of shock features in quartz and feldspar suggests that deformation textures within feldspar can record a wide range of average pressures, starting below that required for shock deformation of quartz. We suggest that experimental analysis of feldspar behavior, combined with detailed mapping of shock metamorphism of feldspar in natural systems, may provide critical data to constrain energy dissipation within impact regimes that experienced low average shock pressures.

Reference
Jaret SJ, Kah LC and Harris RS (in press) Progressive deformation of feldspar recording low-barometry impact processes, Tenoumer impact structure, Mauritania. Meteoritics & Planetary Science
[doi:10.1111/maps.12310]
Published by arrangement with John Wiley & Sons

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Nan Liu^1,2,3, Roberto Gallino⁴, Sara Bisterzo^4,5, Andrew M. Davis^1,2,6, Michael R. Savina^2,3, and Michael J. Pellin^1,2,3,6

¹Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637, USA
²Chicago Center for Cosmochemistry, Chicago, IL 60637, USA
³Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
⁴Dipartimento di Fisica, Università di Torino, Torino I-10125, Italy
⁵INAF-Osservatorio Astrofisico di Torino-Strada Osservatorio 20, Pino Torinese I-10025, Italy
⁶Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA

We present postprocess asymptotic giant branch (AGB) nucleosynthesis models with different ¹³C-pocket internal structures to better explain zirconium isotope measurements in mainstream presolar SiC grains by Nicolussi et al. and Barzyk et al. We show that higher-than-solar ⁹²Zr/⁹⁴Zr ratios can be predicted by adopting a ¹³C-pocket with a flat ¹³C profile, instead of the previous decreasing-with-depth ¹³C profile. The improved agreement between grain data for zirconium isotopes and AGB models provides additional support for a recent proposal of a flat ¹³C profile based on barium isotopes in mainstream SiC grains by Liu et al.

Reference
Liu N, Gallino R, Bisterzo S, Davis AM, Savina MR and Pellin MJ (in press) The 13C-Pocket Structure in AGB Models: Constraints from Zirconium Isotope Abundances in Single Mainstream SiC Grains. The Astrophysical Journal Letters 788:163.
[doi:10.1088/0004-637X/788/2/163]

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Jaime E. Pineda¹, Sascha P. Quanz¹, Farzana Meru¹, Gijs D. Mulders², Michael R. Meyer¹, Olja Panić³ and Henning Avenhaus¹

¹Institute for Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich, Switzerland
²Lunar and Planetary Laboratory, The University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721, USA
³Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK

The disk around the Herbig Ae/Be star HD 100546 has been extensively studied and it is one of the systems for which there are observational indications of ongoing and/or recent planet formation. However, up until now, no resolved image of the millimeter dust emission or the gas has been published. We present the first resolved images of the disk around HD 100546 obtained in Band 7 with the ALMA observatory. The CO (3-2) image reveals a gas disk that extends out to 350 au radius at the 3σ level. Surprisingly, the 870 μm dust continuum emission is compact (radius <60 au) and asymmetric. The dust emission is well matched by a truncated disk with an outer radius of 50 au. The lack of millimeter-sized particles outside 60 au is consistent with radial drift of particles of this size. The protoplanet candidate, identified in previous high-contrast NACO/VLT L‘ observations, could be related to the sharp outer edge of the millimeter-sized particles. Future higher angular resolution ALMA observations are needed to determine the detailed properties of the millimeter emission and the gas kinematics in the inner region (<2”). Such observations could also reveal the presence of a planet through the detection of circumplanetary disk material.

Reference
Pineda JE, Quanz SP, Meru F, Mulders GD, Meyer MR, Panić O and Avenhaus H (in press) Resolved Images of the Protoplanetary Disk around HD 100546 with ALMA. The Astrophysical Journal Letters
[doi:10.1088/2041-8205/788/2/L34]

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K. Nishiizumi¹, M. W. Caffee², Y. Hamajima³, R. C. Reedy⁴ and K. C. Welten¹

¹Space Sciences Laboratory, University of California, Berkeley, California, USA
²Department of Physics, Purdue University, West Lafayette, Indiana, USA
³Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa, Japan
⁴Planetary Science Institute, Los Alamos, New Mexico, USA

The Sutter’s Mill (SM) carbonaceous chondrite fell in California on April 22, 2012. The cosmogenic radionuclide data indicate that Sutter’s Mill was exposed to cosmic rays for 0.082 ± 0.008 Myr, which is one of the shortest ages for C chondrites, but overlaps with a small cluster at approximately 0.1 Myr. The age is significantly longer than proposed ages that were obtained from cosmogenic noble gas concentrations, which have large uncertainties due to trapped noble gas corrections. The presence of neutron-capture ⁶⁰Co and ³⁶Cl in SM indicates a minimum preatmospheric radius of approximately 50 cm, and is consistent with a radius of 1–2 m, as derived from the fireball observations. Although a large preatmospheric size was proposed, one fragment (SM18) contains solar cosmic ray–produced short-lived radionuclides, such as ⁵⁶Co and ⁵¹Cr. This implies that this specimen was less than 2 cm from the preatmospheric surface of Sutter’s Mill. Although this conclusion seems surprising, it is consistent with the observation that the meteoroid fragmented high in the atmosphere. The presence of SCR-produced nuclides is consistent with the high SCR fluxes observed during the last few months before the meteorite’s fall, when its orbit was less than 1 AU from the Sun.

Reference
Nishiizumi K, Caffee MW, Hamajima Y, Reedy RC and Welten KC (in press) Exposure history of the Sutter’s Mill carbonaceous chondrite. Meteoritics & Planetary Science
[doi:10.1111/maps.12297]
Published by arrangement with John Wiley & Sons

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Natalia S. Bezaeva¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Earth Physics Department, Faculty of Physics, M.V. Lomonosov Moscow State University, Moscow, Russia

Here we characterize the magnetic properties of the Chelyabinsk chondrite (LL5, S4, W0) and constrain the composition, concentration, grain size distribution, and mineral fabric of the meteorite’s magnetic mineral assemblage. Data were collected from 10 to 1073 K and include measurements of low-field magnetic susceptibility (χ₀), the anisotropy of χ₀, hysteresis loops, first-order reversal curves, Mössbauer spectroscopy, and X-ray microtomography. The REM and REM′ paleointensity protocols suggest that the only magnetizations recorded by the chondrite are components of the Earth’s magnetic field acquired during entry into our planet’s atmosphere. The Chelyabinsk chondrite consists of light and dark lithologies. Fragments of the light lithology show logχ₀ = 4.57 ± 0.09 (s.d.) (n = 135), while the dark lithology shows 4.65 ± 0.09 (n = 39) (where χ₀ is in 10⁻⁹ m³ kg⁻¹). Thus, Chelyabinsk is three times more magnetic than the average LL5 fall, but is similar to a subgroup of metal-rich LL5 chondrites (Paragould, Aldsworth, Bawku, Richmond) and L/LL5 chondrites (Glanerbrug, Knyahinya). The meteorite’s room-temperature magnetization is dominated by multidomain FeNi alloys taenite and kamacite (no tetrataenite is present). However, below approximately 75 K remanence is dominated by chromite. The metal contents of the light and dark lithologies are 3.7 and 4.1 wt%, respectively, and are based on values of saturation magnetization.

Reference
Bezaeva et al. (in press) Magnetic properties of the LL5 ordinary chondrite Chelyabinsk (fall of February 15, 2013). Meteoritics & Planetary Science
[doi:10.1111/maps.12307]
Published by arrangement with John Wiley & Sons

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David R. Frank^a, Michael E. Zolensky^b and Loan Le^a

^aESCG, NASA Johnson Space Center, Houston, TX 77058, USA
^bAstromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058, USA

The dearth of both major and minor element analyses of anhydrous silicate phases in chondrite matrix has thus far hindered their comparison to the Wild 2 samples. We present 68 analyses of olivine (Fa_0-97) in the coarse-grained terminal particles of Stardust aerogel tracks and a comprehensive dataset (> 10³ analyses) of analogous olivine grains (5-30μm) isolated in CI, CM, CR, CH, CO, CV3-oxidized, CV3-reduced, C3-ungrouped (Acfer 094 and Ningqiang), L/LL 3.0-4, EH3, and Kakangari chondrite matrix. These compositions reveal that Wild 2 likely accreted a diverse assortment of material that was radially transported from various carbonaceous and ordinary chondrite-forming regions. The Wild 2 olivine includes ameoboid olivine aggregates (AOAs), refractory forsterite, type I and type II chondrule fragments and/or microchondrules, and rare relict grain compositions. In addition, we have identified one terminal particle that has no known compositional analog in the meteorite record and may be a signature of low-temperature, aqueous processing in the Kuiper Belt. The generally low Cr content of FeO-rich olivine in the Stardust samples indicates that they underwent mild thermal metamorphism, akin to a petrologic grade of 3.05-3.15.

Reference
Frank DR, Zolensky ME and Le L (in press) Olivine in terminal particles of Stardust aerogel tracks and analogous grains in chondrite matrix. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2014.05.037]
Copyright Elsevier

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Alan E. Rubin

Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, USA

MIL 11207 (R6) and LAP 04840 (R6) contain hornblende and phlogopite; MIL 07440 (R6) contains accessory titan-phlogopite and no hornblende. All three meteorites have been shocked: MIL 11207 contains extensive sulfide veins, pyroxene that formed from dehydrated hornblende, and an extensive network of plagioclase glass; MIL 07440 contains chromite-plagioclase assemblages, chromite veinlets and blebs, pincer-shaped plagioclase patches, but no sulfide veins; LAP 04840 contains olivine grains with chromite-bleb-laden cores and opaque-free rims, rare grains of pyroxene that formed from dehydrated hornblende, and no sulfide veins. These meteorites appear to have been heated to maximum temperatures of approximately 700–900 °C under conditions of moderately high PH₂O (perhaps 250–500 bars). All three samples underwent postshock annealing. During this process, olivine crystal lattices healed (giving the rocks the appearance of shock-stage S1), and diffusion of Fe and S from thin sulfide veins to coarse sulfide grains caused the veins to disappear in MIL 07440 and LAP 04840. This latter process apparently also occurred in most S1–S2 ordinary chondrites of high petrologic type. The pressure–temperature conditions responsible for forming the amphibole and mica in these rocks may have been present at depths of a few tens of kilometers (as suggested in the literature). A giant impact or a series of smaller impacts would then have been required to excavate the hornblende- and biotite-bearing rocks and bring them closer to the surface. It was in that latter location where the samples were shocked, deposited in a hot ejecta blanket of low thermal diffusivity, and annealed.

Reference
Rubin AE (in press) Shock and annealing in the amphibole- and mica-bearing R chondrites. Meteoritics & Planetary Science
[doi:10.1111/maps.12315]
Published by arrangement with John Wiley & Sons

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Andreas Morlok^a,b, Andrew B. Mason^c, Mahesh Anand^a,b, Carey Lisse^d, Emma S. Bullock^e and Monica Grady^a,b

^aDepartment of Earth Sciences, The Natural History Museum, London, SW7 5BD, UK
^bPlanetary and Space Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA UK
^cFinnish Centre for Astronomy with ESO (FINCA), University of Turku, Tuorla Observatory, Väisäläntie 20, FI-21500 Piikkiö, Finland
^dJohns Hopkins University -APL, 11100 Johns Hopkins Road, Laurel, MD 20723, USA
^eDepartment of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington DC 20560, USA

In order to link infrared observations of dust formed during planet formation in debris disks to mid-infrared spectroscopic data of planetary materials from differentiated terrestrial and asteroidal bodies, we obtained absorption spectra of a representative suite of terrestrial crustal and mantle materials, and of typical Martian meteorites.
A series of debris disk spectra characterized by a strong feature in the 9.0-9.5 μm range (HD23514, HD15407a, HD172555 and HD165014), is comparable to materials that underwent shock, collision or high temperature events. These are amorphous materials such as tektites, SiO₂-glass, obsidian, and highly shocked shergottites as well as inclusions from mesosiderites (Group A).
A second group (BD+20307, Beta Pictoris, HD145263, ID8, HD113766, HD69830, P1121, and Eta Corvi) have strong pyroxene and olivine bands in the 9-12 μm range and is very similar to ultramafic rocks (e.g. harzburgite, dunite)(Group B).
This could indicate the occurrence of differentiated materials similar to those in our Solar System in these other systems.
However, mixing of projectile and target material, as well as that of crustal and mantle material has to be taken into account in large scale events like hit-and-run and giant collisions or even large-scale planetary impacts. This could explain the olivine-dominated dust of group B.
The crustal-type material of group A would possibly require the stripping of upper layers by grazing-style hit-and run encounters or high energy events like evaporation/condensation in giant collisions. In tidal disruptions or the involvement of predominantly icy/water bodies the resulting mineral dust would originate mainly in one of the involved planetesimals. This could allow attributing the observed composition to a specific body (such as e.g. Eta Corvi).

Reference
Morlok M, Mason AB, Anand M, Lisse C, Bullock ES and Grady M (in press) Dust from collisions: A way to probe the composition of exo-planets?. Icarus
[doi:10.1016/j.icarus.2014.05.024]
Copyright Elsevier

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Daniel Herwartz^1,2, Andreas Pack¹, Bjarne Friedrichs¹ and Addi Bischoff³

¹Georg-August-Universität Göttingen, Geowissenschaftliches Zentrum, Abteilung Isotopengeologie, Goldschmidtstraße 1, 37073 Göttingen, Germany.
²Universität zu Köln, Institut für Geologie und Mineralogie, Zülpicher Straße 49a, 50674 Köln, Germany.
³Westfälische Wilhelms-Universität Münster, Institut für Planetologie, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany.

The Moon was probably formed by a catastrophic collision of the proto-Earth with a planetesimal named Theia. Most numerical models of this collision imply a higher portion of Theia in the Moon than in Earth. Because of the isotope heterogeneity among solar system bodies, the isotopic composition of Earth and the Moon should thus be distinct. So far, however, all attempts to identify the isotopic component of Theia in lunar rocks have failed. Our triple oxygen isotope data reveal a 12 ± 3 parts per million difference in Δ¹⁷O between Earth and the Moon, which supports the giant impact hypothesis of Moon formation. We also show that enstatite chondrites and Earth have different Δ¹⁷O values, and we speculate on an enstatite chondrite–like composition of Theia. The observed small compositional difference could alternatively be explained by a carbonaceous chondrite–dominated late veneer.

Reference
Herwartz D, Pack A, Friedrichs B and Bischoff A (in press) Identification of the giant impactor Theia in lunar rocks. Science 344:1146.
[doi:10.1126/science.1251117]
Reprinted with permission from AAAS

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