¹Roshchin, V.E. , ¹Goikhenberg, Y.N., ¹Galimov, D.M.
¹Southern Ural State University, Chelyabinsk, Russian Federation

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Reference
Roshchin VE, Goikhenberg YN, Galimov DM (2014) Native metal of the Chelyabinsk Meteorite.
Russian Metallurgy (Metally) 2014-5, 419-425
Link to Article [DOI: 10.1134/S0036029514050103]

^1,2Jon M. Friedrich,^2,3,4Michael K. Weisberg,^2,4,5Denton S. Ebel,⁶Alison E. Biltz,⁶Bernadette M. Corbett,⁶Ivan V. Iotzov,⁶Wajiha S. Khan,⁶Matthew D. Wolman
¹Department of Chemistry, Fordham University, Bronx, NY 10458, USA
²Department of Earth and Planetary Sciences, American Museum of Natural History, New York, NY 10024, USA
³Department of Physical Sciences, Kingsborough College of the City University of New York, Brooklyn, NY 11235, USA
⁴Graduate Center of the City University of New York, 365 5th Ave, New York, NY 10016, USA
⁵Lamont–Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA
⁶Fordham College at Rose Hill, Fordham University, Bronx, NY 10458, USA

The examination of the physical properties of chondrules has generally received less emphasis than other properties of meteorites such as their mineralogy, petrology, and chemical and isotopic compositions. Among the various physical properties of chondrules, chondrule size is especially important for the classification of chondrites into chemical groups, since each chemical group possesses a distinct size-frequency distribution of chondrules. Knowledge of the physical properties of chondrules is also vital for the development of astrophysical models for chondrule formation, and for understanding how to utilize asteroidal resources in space exploration. To examine our current knowledge of chondrule sizes, we have compiled and provide commentary on available chondrule dimension literature data. We include all chondrite chemical groups as well as the acapulcoite primitive achondrites, some of which contain relict chondrules. We also compile and review current literature data for other astrophysically-relevant physical properties (chondrule mass and density). Finally, we briefly examine some additional physical aspects of chondrules such as the frequencies of compound and “cratered” chondrules. A purpose of this compilation is to provide a useful resource for meteoriticists and astrophysicists alike.

Reference
Friedrich JM, Weisberg MK,Ebel DS, Biltz AE, Corbett BM, Iotzov IV, Khan WS, Wolman MD (2014) Chondrule size and related physical properties: A compilation and evaluation of current data across all meteorite Groups. Chemie der Erde (in Press)
Link to Article [DOI: 10.1016/j.chemer.2014.08.003]

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¹Alexander Hubbard,² Denton S. Ebel
¹Department of Astrophysics, American Museum of Natural History, New York, NY 10024-5192, USA
²Department of Earth and Planetary Sciences, American Museum of Natural History, New York, NY 10024-5192, USA

We consider the evidence presented by the LL3.0 chondrite Semarkona, including its chondrule fraction, chondrule size distribution and matrix thermal history. We show that no more than a modest fraction of the ambient matrix material in the Solar Nebula could have been melted into chondrules; and that much of the unprocessed matrix material must have been filtered out at some stage of Semarkona’s parent body formation process. We conclude that agglomerations of many chondrules must have formed in the Solar Nebula, which implies that chondrules and matrix grains had quite different collisional sticking parameters. Further, we note that the absence of large melted objects in Semarkona means that chondrules must have exited the melting zone rapidly, before the chondrule agglomerations could form. The simplest explanation for this rapid exit is that chondrule melting occurred in surface layers of the disk. The newly formed, compact, chondrules then settled out of those layers on short time scales.

Reference
Hubbard A, Ebel DS (2014) Semarkona: Lessons for chondrule and chondrite Formation. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.09.025]

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¹David Parry Rubincam
¹Code 698, Planetary Geodynamics Laboratory, Solar System Exploration Division, NASA Goddard Space Flight Center, Building 34, Room S280 Greenbelt, MD 20771

Space erosion from dust impacts may set upper limits on the cosmic ray exposure (CRE) ages of stony meteorites. A meteoroid orbiting within the asteroid belt is bombarded by both cosmic rays and interplanetary dust particles. Galactic cosmic rays penetrate only the first few meters of the meteoroid; deeper regions are shielded. The dust particle impacts create tiny craters on the meteoroid’s surface, eroding it away by abrasion at a particular rate. Hence a particular point inside a meteoroid accumulates cosmic ray products only until that point wears away, limiting CRE ages. The results would apply to other regolith-free surfaces in the solar system as well, so that abrasion may set upper CRE age limits which depend on the dusty environment. Calculations based on N. Divine’s dust populations and on micrometeoroid cratering indicate that large stony meteoroids in circular ecliptic orbits at 2 AU will record 21Ne CRE ages of ∼176 × 106 years if dust masses are in the range 10-21 – 10-3 kg. This is in broad agreement with the maximum observed CRE ages of ∼100 × 106 years for stones. High erosion rates in the inner solar system may limit the CRE ages of Near-Earth Asteroids (NEAs) to ∼120 × 106 years. A characteristic of erosion is that the neon concentrations tend to rise as the surface of the meteorite is approached, rather than drop off as for meteorites with fixed radii. Pristine samples recovered from space may show the rise. If the abrasion rate for stones were a factor of ∼6 larger than found here, then the ages would drop into the 30 × 106 y range, so that abrasion alone might be able to explain many CRE ages. However, there is no strong evidence for higher abrasion rates, and in any case would probably not be fast enough to explain the youngest ages of 0.1 – 1 × 106 y. Further, space erosion is much too slow to explain the ∼600 × 106 y ages of iron meteorites.

Reference
Rubincam DP (2014) Space erosion and cosmic ray exposure ages of stony meteorites. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.09.005]

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¹Michael K. Shepard et al. (>10)*
¹Bloomsburg University, 400 E. Second St., Bloomsburg, PA 17815, USA
*Find the extensive, full author and affiliation list on the publishers website

Using the S-band radar at Arecibo Observatory, we observed thirteen X/M-class asteroids; nine were previously undetected and four were re-observed, bringing the total number of Tholen X/M-class asteroids observed with radar to 29. Of these 29 M-class asteroids, 13 are also W-class, defined as M-class objects that also display a 3-micron absorption feature which is often interpreted as the signature of hydrated minerals (Jones et al. Icarus 88, 172-192, 1990; Rivkin et al. Icarus 117, 90-100, 1995; Icarus 145, 351-368, 2000).
Consistent with our previous work (Shepard et al., 2008 and Shepard et al., 2011), we find that 38% of our sample (11 of 29) have radar albedos consistent with metal-dominated compositions. With the exception of 83 Beatrix and 572 Rebekka, the remaining objects have radar albedos significantly higher than the mean S- or C-class asteroid (Magri et al. Icarus 186, 126-151, 2007).
Seven of the eleven high-radar-albedo asteroids, or 64%, also display a 3-micron absorption feature (W-class) which is thought to be inconsistent with the formation of a metal dominated asteroid. We suggest that the hydration absorption could be a secondary feature caused by low-velocity collisions with hydrated asteroids, such as CI or CM analogs, and subsequent implantation of the hydrated minerals into the upper regolith. There is recent evidence for this process on Vesta (Reddy et al. Icarus 221, 544-559, 2012; McCord et al. Nature 491, 83-86, 2012; Prettyman et al. Science 338, 242-246, 2012; Denevi et al. Science 338, 246-249, 2012).
Eleven members of our sample show bifurcated radar echoes at some rotation phases; eight of these are high radar targets. One interpretation of a bifurcated echo is a contact binary, like 216 Kleopatra, and several of our sample are contact binary candidates. However, evidence for other targets indicates they are not contact binaries. Instead, we hypothesize that these asteroids may have large-scale variations in surface bulk density, i.e. isolated patches of metal-rich and silicate-rich regions at the near-surface, possibly the result of collisions between metal and silicate-rich asteroids.

Reference
Shepard MK et al. (2014) A radar survey of M- and X-class asteroids. III. Insights into their composition, hydration state, & structure. Icarus (in Press)
Link to Article: [DOI: 10.1016/j.icarus.2014.09.016]

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¹Paula Lindgren,^1,2Romy D. Hanna,^3,4Katherine J. Dobson,
⁵Tim Tomkinson, ¹Martin R. Lee

¹School of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK
²Jackson School of Geological Sciences, University of Texas, Austin TX 78712, USA
³Manchester X-ray Imaging Facility, School of Materials, University of Manchester, Manchester M13 9PL, UK
⁴Research Complex at Harwell, Rutherford Appleton Laboratories, Oxfordshire OX11 0FA, UK
⁵Scottish Universities Environmental Research Centre, East Kilbride E75 0QF, UK

Petrographic analysis of eight CM carbonaceous chondrites (EET 96029, LAP 031166, LON 94101, MET 01072, Murchison, Murray, SCO 06043, QUE 93005) by electron imaging and diffraction, and X-ray computed tomography, reveals that six of them have a petrofabric defined by shock flattened chondrules. With the exception of Murchison, those CMs that have a strong petrofabric also contain open or mineralized fractures, indicating that tensional stresses accompanying the impacts were sufficient to locally exceed the yield strength of the meteorite matrix. The CMs studied span a wide range of petrologic subtypes, and in common of Rubin (Rubin A. E. (2012) Collisional facilitation of aqueous alteration of CM and CV carbonaceous chondrites. Geochim. Cosmochim. Acta90, 181-194) we find that the strength of their petrofabrics increases with their degree of aqueous alteration. This correspondence suggests that impacts were responsible for enhancing alteration, probably because the fracture networks they formed tapped fluid reservoirs elsewhere in the parent body. Two meteorites that do not fit this pattern are MET 01072 and Murchison; both have a strong petrofabric but are relatively unaltered. In the case of MET 01072, impact deformation is likely to have postdated parent body aqueous activity. The same may also be true for Murchison, but as this meteorite also lacks fractures and veins, its chondrules were most likely flattened by multiple low intensity impacts. Multiphase deformation of Murchison is also revealed by the microstructures of calcite grains, and chondrule-defined petrofabrics as revealed by X-ray computed tomography. The contradiction between the commonplace evidence for impact-deformation of CMs and their low shock stages (most belong to S1) can be explained by most if not all having been exposed to multiple low intensity (i.e.

Reference
Lindgren P, Hanna RD, Dobson KJ, Tomkinson T, Lee MR (2014) The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity Impacts. Geochimica et Cosmochimica Acta (in Press)
Link to Article [DOI: 10.1016/j.gca.2014.09.014]

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¹Falko Langenhorst, ¹Dennis Harries, ¹Kilian Pollok, ²Peter A van Aken
¹Analytical Mineralogy of Micro- and Nanostructures, Institute of Geoscience,
Friedrich Schiller University Jena, Carl-Zeiss-Promenade 10, D-07745 Jena,
Germany
²Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, D-70569
Stuttgart, Germany

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Langenhorst F, Harries D, Pollok K, van Aken PA (2014) Mineralogy and defect microstructure of an olivine-dominated Itokawa dust particle: evidence for shock metamorphism, collisional fragmentation, and LL chondrite origin. Earth, Planets and Space, 66:118
Link to Article [doi:10.1186/1880-5981-66-118]

¹Klaus Hornung et al. (>10)*
¹Dept. of Aerospace Engineering, Universität der Bundeswehr München, Werner-Heisenberg-Weg 39, D-85577 Neubiberg, Germany
*Find the extensive, full author and affiliation list on the publishers website

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Reference
Hornung K. et al. (2014) Collecting Cometary Dust Particles on Metal Blacks with The COSIMA Instrument Onboard ROSETTA. Planetary and Space Science (in Press)
Link to Article [DOI: 10.1016/j.pss.2014.08.011]

¹John Anfinogenov,²Larisa Budaeva,³Dmitry Kuznetsov,
³Yana Anfinogenova

¹The Tungussky Nature Reserve, the Ministry of Natural Resources and Ecology of the Russian Federation
²The National Research Tomsk State University, the Ministry of Education and Science of the Russian Federation
³The National Research Tomsk Polytechnic University, the Ministry of Education and Science of the Russian Federation

The aim of this study was to discover remnants of the 1908 Tunguska meteorite. Field studies identified exotic rocks, furrows, and penetration funnels reported by the first eyewitnesses. Main methods included decoding of aerial survey photographs, systematic survey of epicenter area of the Tunguska explosion, exploratory excavations, reconstruction studies of the exotic rocks, mineralogical and spectral analysis of specimens, and experimental attempt of plasma-induced reproduction of fusion crust. The authors report the discovery of funnel-like structures and of an exotic boulder known as John’s Stone (JS) in the epicentral area. The article provides detailed description of JS, fresh furrows in the permafrost, multiple shear-fractured splinters, splinters with glassy coatings, evidence of high-speed impact of JS in the ground, and clear consistency in the geometry of spacial arrangements of all splinters, furrows, and cleaved pebbles. Pattern of permafrost destruction suggested about high-speed entry and lateral ricochet of JS in the ground with further deceleration and breakage. Calculated landing velocity of JS was at least 547 m/s. John’s Stone is composed of highly silicified gravelite sandstone (98.5% SiO2) with grain size of 0.5 to 1.5 cm. Outer surface of several splinters showed continuous glassy coating similar to shiny fusion crust reminiscent of freshly applied enamel. Plasma-induced heating of John’s Stone specimen led to its explosive disintegration; residue presented with light-colored semi-transparent pumice-like grains and irregularly shaped fused particles. Overall, our data suggest that John’s Stone may be a fragment of the 1908 Tunguska meteorite and may represent a new type of meteorite.

Reference
Anfinogenov J, Budaeva L, Kuznetsov D, Anfinogenova Y (2014) John’s Stone: a possible fragment of the 1908 Tunguska Meteorite. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.09.006]

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¹Melissa J. Dykhuis,²Lawrence Molnar,²Samuel J. Van Kooten,
¹Richard Greenberg

¹Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85719, USA
²Calvin College, 3201 Burton St SE, Grand Rapids, MI 49546, USA

The Flora family resides in the densely populated inner main belt, bounded in semimajor axis by the ν6ν6 secular resonance and the Jupiter 3:1 mean motion resonance. The presence of several large families that overlap dynamically with the Floras (e.g., the Vesta, Baptistina, and Nysa-Polana families), and the removal of a significant fraction of Floras via the nearby ν6ν6 resonance complicates the Flora family’s distinction in both proper orbital elements and reflectance properties. Here we use orbital information from the Asteroids Dynamic Site (AstDyS), color information from the Sloan Digital Sky Survey (SDSS), and albedo information from the Wide-field Infrared Survey Explorer (WISE) to obtain the median orbital and reflectance properties of the Floras by sampling the core of the family in multidimensional phase space. We find the median Flora SDSS colors to be a∗a∗ = 0.126 ± 0.007 and i-z=-0.037±0.007i-z=-0.037±0.007; the median Flora albedo is pVpV = 0.291 ± 0.012. These properties allow us to define ranges for the Flora family in orbital and reflectance properties, as required for a detailed dynamical study. We use the young Karin family, for which we have an age determined via direct backward integration of members’ orbits, to calibrate the Yarkovsky drift rates for the Flora family without having to estimate the Floras’ material properties. The size-dependent dispersion of the Flora members in semimajor axis (the “V” plot) then yields an age for the family of View the MathML source950-170+200 My, with the uncertainty dominated by the uncertainty in the material properties of the family members (e.g., density and surface thermal properties). We discuss the effects on our age estimate of two independent processes that both introduce obliquity variations among the family members on short (My) timescales: 1) the capture of Flora members in spin-orbit resonance, and 2) YORP-driven obliquity variation through YORP cycles. Accounting for these effects does not significantly change this age determination.

Reference
Dykhuis MJ, Molnar L, Van Kooten SJ, Greenberg R (2014) Defining the Flora Family: Orbital Properties, Reflectance Properties and Age. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.09.011]

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