J. R. Lyons†

Department of Earth & Space Sciences, UCLA, Los Angeles, California, USA
^†School of Earth & Space Exploration, Arizona State University, Tempe, Arizona, USA

CO photodissociation in the solar nebula and/or parent cloud has been proposed to be the mechanism responsible for forming the ¹⁶O-poor reservoir of the calcium-aluminum-rich inclusion (CAI) mixing line. However, laboratory experiments on CO photolysis found a wavelength dependence in the oxygen isotope ratios of the product O atoms, which was interpreted as proof that CO photolysis was not a viable mechanism. Here, I report photochemical simulations of these experiments using line-by-line CO spectra to identify the origin of the wavelength dependence. At long wavelengths (>105 nm), the line-by-line spectra for isotopic CO can explain the experimental data with a combination of C¹⁶O self-shielding and reduced dissociation probabilities for C¹⁸O. At short wavelengths, the greater number of diffuse bands increases the importance of mass-dependent fractionation, lowering the slope to below unity. The line-by-line isotopic spectra are then applied to CO photodissociation in a model solar nebula. Three FUV sources are considered (1) HD 303308, an O4 star in Carina; (2) HD 36981, a B5 star in Orion; and (3) TW Hydrae, a T Tauri star of 10 Myr age. Using reduced dissociation probabilities for C¹⁸O based on the photolysis experiments yields nebular water slopes approximately 0.95–1.0 for HD 303308 and TW Hya, and approximately 0.8–1.5 for HD 36981. For the central protostar case (TW Hya) with a simplified treatment of the 2-D radiative transfer, slopes approximately 0.95–1.0 are obtained, independent of the C¹⁸O dissociation probability. Greatly improved measurements of the C¹⁷O and C¹⁸O cross sections and dissociation probabilities are in progress.

Reference
Lyons JR (in press) Photodissociation of CO isotopologues: Models of laboratory experiments and implications for the solar nebula. Meteoritics & Planetary Science
[doi:10.1111/maps.12246]
Published by arrangement with John Wiley & Sons

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Marc Fries¹, Lucille Le Corre², Mike Hankey³, Jeff Fries⁴, Robert Matson⁵, Jake Schaefer⁶, Vishnu Reddy⁷

¹NASA Astromaterials Research and Exploration Science (ARES), Mail Code KT, Johnson Space Center, Houston, Texas, USA
²Planetary Science Institute, Tucson, Arizona, USA
³American Meteor Society, Monkton, Maryland, USA
⁴First Weather Group, Air Force Weather Agency, Offutt AFB, Nebraska, USA
⁵Science Applications International Corp., Seal Beach, California, USA
⁶NASA Dryden, Edwards, California, USA
⁷Planetary Science Institute, Tucson, Arizona, USA

The Sutter’s Mill C-type meteorite fall occurred on 22 April 2012 in and around the town of Coloma, California. The exact location of the meteorite fall was determined within hours of the event using a combination of eyewitness reports, weather radar imagery, and seismometry data. Recovery of the first meteorites occurred within 2 days and continued for months afterward. The recovery effort included local citizens, scientists, and meteorite hunters, and featured coordination efforts by local scientific institutions. Scientific analysis of the collected meteorites revealed characteristics that were available for study only because the rapid collection of samples had minimized terrestrial contamination/alteration. This combination of factors—rapid and accurate location of the event, participation in the meteorite search by the public, and coordinated scientific investigation of recovered samples—is a model that was widely beneficial and should be emulated in future meteorite falls. The tools necessary to recreate the Sutter’s Mill recovery are available, but are currently underutilized in much of the world. Weather radar networks, scientific institutions with interest in meteoritics, and the interested public are available globally. Therefore, it is possible to repeat the Sutter’s Mill recovery model for future meteorite falls around the world, each for relatively little cost with a dedicated researcher. Doing so will significantly increase the number of fresh meteorite falls available for study, provide meteorite material that can serve as the nuclei of new meteorite collections, and will improve the public visibility of meteoritics research.

Reference
Fries M, Le Corre L, Hankey M, Fries J, Matson R, Schaefer J and Reddy V (in press) Detection and rapid recovery of the Sutter’s Mill meteorite fall as a model for future recoveries worldwide. Meteoritics & Planetary Science
[doi:10.1111/maps.12249]
Published by arrangement with John Wiley & Sons

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J. Ormö¹, E. Sturkell², J. Nõlvak³, I. Melero-Asensio¹, Å. Frisk^4,†, T. Wikström⁵

¹Centro de Astrobiologia (INTA-CSIC), Madrid, Spain
²Department of Earth Sciences, University of Gothenburg, Sweden, Gothenburg, Sweden
³Institute of Geology, Tallinn University of Technology, Tallinn, Estonia
⁴Paläontologisches Institut und Museum, Universität Zürich, Zürich, Switzerland
⁵Stockholm, Sweden
^†Palaeobiology, Department of Earth Sciences, Uppsala University, Uppsala, Sweden

The Målingen structure is an approximately 700 m wide, rimmed, sediment-filled, circular depression in Precambrian crystalline basement approximately 16.2 km from the concentric, marine-target Lockne crater (inner, basement crater diameter approximately 7.5 km, total diameter in sedimentary strata approximately 13.5 km). We present here results from geologic mapping, a 148.8 m deep core drilling from the center of the structure, detailed biostratigraphic dating of the structure’s formation and its age correlation with Lockne, chemostratigraphy of the sedimentary infill, and indication for shock metamorphism in quartz from breccias below the crater infill. The drill core reveals, from bottom to the top, approximately 33 m of basement rocks with increased fracturing upward, approximately 10 m of polymict crystalline breccia with shock features, approximately 97 m of slumped Cambrian mudstone, approximately 4.7 m of a normally graded, polymict sedimentary breccia that in its uppermost part grades into sandstone and siltstone (cf. resurge deposits), and approximately 1.6 m of secular sediments. The combined data set shows that the Målingen structure formed in conjunction with the Lockne crater in the same marine setting. The shape and depth of the basement crater and the cored sequence of crystalline breccias with shocked quartz, slumped sediments, and resurge deposits support an impact origin. The stratigraphic and geographic relationship with Lockne suggests the Lockne and Målingen craters to be the first described doublet impact structure by a binary asteroid into a marine-target setting.

Reference
Ormö J, Sturkell E, Nõlvak J, Melero-Asensio I, Frisk Å and Wikström T (in press) The geology of the Målingen structure: A probable doublet to the Lockne marine-target impact crater, central Sweden. Meteoritics & Planetary Science
[doi:10.1111/maps.12251]
Published by arrangement with John Wiley & Sons

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M. Kimura^1,5, J. A. Barrat², M. K. Weisberg^3,4, N. Imae⁵, A. Yamaguchi⁵, H. Kojima⁵

¹Faculty of Science, Ibaraki University, Mito, Japan
²Université Européenne de Bretagne, 2CNRS UMR 6538 (Domaines Océaniques), U.B.O.-I.U.E.M., Plouzané Cedex, France
³Department of Physical Sciences, Kingsborough College and Graduate School of the City University of New York, Brooklyn, New York, USA
⁴Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA
⁵National Institute of Polar Research, Tokyo, Japan

Carbonaceous chondrites are classified into several groups. However, some are ungrouped. We studied one such ungrouped chondrite, Y-82094, previously classified as a CO. In this chondrite, chondrules occupy 78 vol%, and the matrix is distinctly poor in abundance (11 vol%), compared with CO and other C chondrites. The average chondrule size is 0.33 mm, different from that in C chondrites. Although these features are similar to those in ordinary chondrites, Y-82094 contains 3 vol% Ca-Al-rich inclusions and 5% amoeboid olivine aggregates (AOAs). Also, the bulk composition resembles that of CO chondrites, except for the volatile elements, which are highly depleted. The oxygen isotopic composition of Y-82094 is within the range of CO and CV chondrites. Therefore, Y-82094 is an ungrouped C chondrite, not similar to any other C chondrite previously reported. Thin FeO-rich rims on AOA olivine and the mode of occurrence of Ni-rich metal in the chondrules indicate that Y-82094 is petrologic type 3.2. The extremely low abundance of type II chondrules and high abundance of Fe-Ni metal in the chondrules suggest reducing condition during chondrule formation. The depletion of volatile elements indicates that the components formed under high-temperature conditions, and accreted to the parent body of Y-82094. Our study suggests a wider range of formation conditions than currently recorded by the major C chondrite groups. Additionally, Y-82094 may represent a new, previously unsampled, asteroidal body.

Reference
Kimura M, Barrat JA, Weisberg MK, Imae N, Yamaguchi A and Kojima H (in press) Petrology and bulk chemistry of Yamato-82094, a new type of carbonaceous chondrite. Meteoritics & Planetary Science
[doi:10.1111/maps.12254]
Published by arrangement with John Wiley & Sons

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Philipp R. Heck^1,2 et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Robert A. Pritzker Center for Meteoritics and Polar Studies, The Field Museum, Chicago, Illinois, USA
²Chicago Center for Cosmochemistry, The University of Chicago, Chicago, Illinois, USA

Atom-probe tomography (APT) is currently the only analytical technique that, due to its spatial resolution and detection efficiency, has the potential to measure the carbon isotope ratios of individual nanodiamonds. We describe three different sample preparation protocols that we developed for the APT analysis of meteoritic nanodiamonds at sub-nm resolution and present carbon isotope peak ratios of meteoritic and synthetic nanodiamonds. The results demonstrate an instrumental bias associated with APT that needs to be quantified and corrected to obtain accurate isotope ratios. After this correction is applied, this technique should allow determination of the distribution of ¹²C/¹³C ratios in individual diamond grains, solving the decades-old question of the origin of meteoritic nanodiamonds: what fraction, if any, formed in the solar system and in presolar environments? Furthermore, APT could help us identify the stellar sources of any presolar nanodiamonds that are detected.

Reference
Heck PR et al. (in press) Atom-probe analyses of nanodiamonds from Allende. Meteoritics & Planetary Science. Meteoritics & Planetary Science
[doi:10.1111/maps.12265]
Published by arrangement with John Wiley & Sons

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J. Gattacceca^1,2, C. Suavet¹, P. Rochette², B. P. Weiss¹, M. Winklhofer³, M. Uehara², Jon M. Friedrich^4,5

¹Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
²CNRS, Aix-Marseille Université, Aix en Provence, France
³Department of Earth and Environmental Sciences, Ludwig-Maximilians-University Munich, Munich, Germany
⁴Department of Chemistry, Fordham University, Bronx, New York, USA
⁵Department of Earth and Planetary Sciences, American Museum of Natural History, New York City, New York, USA

Magnetic properties are sensitive proxies to characterize FeNi metal phases in meteorites. We present a data set of magnetic hysteresis properties of 91 ordinary chondrite falls. We show that hysteresis properties are distinctive of individual meteorites while homogeneous among meteorite subsamples. Except for the most primitive chondrites, these properties can be explained by a mixture of multidomain kamacite that dominates the induced magnetism and tetrataenite (both in the cloudy zone as single-domain grains, and as larger multidomain grains in plessite and in the rim of zoned taenite) dominates the remanent magnetism, in agreement with previous microscopic magnetic observations. The bulk metal contents derived from magnetic measurements are in agreement with those estimated previously from chemical analyses. We evidence a decreasing metal content with increasing petrologic type in ordinary chondrites, compatible with oxidation of metal during thermal metamorphism. Types 5 and 6 ordinary chondrites have higher tetrataenite content than type 4 chondrites. This is compatible with lower cooling rates in the 650–450 °C interval for higher petrographic types (consistent with an onion-shell model), but is more likely the result of the oxidation of ordinary chondrites with increasing metamorphism. In equilibrated chondrites, shock-related transient heating events above approximately 500 °C result in the disordering of tetrataenite and associated drastic change in magnetic properties. As a good indicator of the amount of tetrataenite, hysteresis properties are a very sensitive proxy of the thermal history of ordinary chondrites, revealing low cooling rates during thermal metamorphism and high cooling rates (e.g., following shock reheating or excavation after thermal metamorphism). Our data strengthen the view that the poor magnetic recording properties of multidomain kamacite and the secondary origin of tetrataenite make equilibrated ordinary chondrites challenging targets for paleomagnetic study.

Reference
Beck P et al. (in press) Metal phases in ordinary chondrites: Magnetic hysteresis properties and implications for thermal history. Meteoritics & Planetary Science
[doi:10.1111/maps.12268]
Published by arrangement with John Wiley & Sons

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