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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