¹Pavel P. Povinec et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website
¹Department of Nuclear Physics and Biophysics, Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia

On February 15, 2013, after the observation of a brilliant fireball and a spectacular airburst over the southern Ural region (Russia), thousands of stones fell and were rapidly recovered, bringing some extremely fresh material for scientific investigations. We undertook a multidisciplinary study of a dozen stones of the Chelyabinsk meteorite, including petrographic and microprobe investigations to unravel intrinsic characteristics of this meteorite. We also study the short and long-lived cosmogenic radionuclides to characterize the initial meteoroid size and exposure age. Petrographic observations, as well as the mineral compositions obtained by electron microprobe analyses, allow us to confirm the classification of the Chelyabinsk meteorite as an LL5 chondrite. The fragments studied, a few of which are impact melt rocks, contain abundant shock melt veins and melt pockets. It is likely that the catastrophic explosion and fragmentation of the Chelyabinsk meteoroid into thousands of stones was in part determined by the initial state of the meteoroid. The radionuclide results obtained show a wide range of concentrations of 14C, 22Na, 26Al, 54Mn, 57Co, 58Co, and 60Co, which indicate that the pre-atmospheric object had a radius >5 m, consistent with other size estimates based on the magnitude of the airburst caused by the atmospheric entry and breakup of the Chelyabinsk meteoroid. Considering the observed 26Al activities of the investigated samples, Monte Carlo simulations, and taking into account the 26Al half-life (0.717 Myr), the cosmic-ray exposure age of the Chelyabinsk meteorite is estimated to be 1.2 ± 0.2 Myr. In contrast to the other radionuclides, 14C showed a very large range only consistent with most samples having been exposed to anthropogenic sources of 14C, which we associate with radioactive contamination of the Chelyabinsk region by past nuclear accidents and waste disposal, which has also been confirmed by elevated levels of anthropogenic 137Cs and primordial 40K in some of the Chelyabinsk fragments.

Reference
Povinec PP et al. (2015) Cosmogenic radionuclides and mineralogical properties of the Chelyabinsk (LL5) meteorite: What do we learn about the meteoroid? Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12419]

Published by arrangement with John Wiley&Sons

^1,2A. Calzada-Diaz, ³K. H. Joy, ^1,2I. A. Crawford, ^2,4T. A. Nordheim
¹Department of Earth and Planetary Sciences, Birkbeck College, London, UK
²Centre for Planetary Sciences UCL/Birkbeck, London, UK
³School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK
⁴Mullard Space Science Laboratory, University College London, Dorking, UK

Lunar meteorites provide important new samples of the Moon remote from regions visited by the Apollo and Luna sample return missions. Petrologic and geochemical analysis of these meteorites, combined with orbital remote sensing measurements, have enabled additional discoveries about the composition and age of the lunar surface on a global scale. However, the interpretation of these samples is limited by the fact that we do not know the source region of any individual lunar meteorite. Here, we investigate the link between meteorite and source region on the Moon using the Lunar Prospector gamma ray spectrometer remote sensing data set for the elements Fe, Ti, and Th. The approach has been validated using Apollo and Luna bulk regolith samples, and we have applied it to 48 meteorites excluding paired stones. Our approach is able broadly to differentiate the best compositional matches as potential regions of origin for the various classes of lunar meteorites. Basaltic and intermediate Fe regolith breccia meteorites are found to have the best constrained potential launch sites, with some impact breccias and pristine mare basalts also having reasonably well-defined potential source regions. Launch areas for highland feldspathic meteorites are much less well constrained and the addition of another element, such as Mg, will probably be required to identify potential source regions for these.

Reference
Calzada-Diaz A, Joy KH, Crawford IA, Nordheim TA (2015) Constraining the source regions of lunar meteorites using orbital geochemical data. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12412]
Published by arrangement with John Wiley&Sons

^1,2,3H. Downes, ⁴F. A. J. Abernethy, ³C. L. Smith, ^2,3,5A. J. Ross, ⁴A. B. Verchovsky, ⁴M. M. Grady, ⁶P. Jenniskens,⁷M. H. Shaddad
¹Department of Earth and Planetary Sciences, Birkbeck University of London, London, UK
²UCL/Birkbeck Centre for Planetary Sciences, UCL, London, UK
³Department of Earth Sciences, Natural History Museum, London, UK
⁴Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes, UK
⁵Department of Earth Sciences, University College London, London, UK
⁶SETI Institute, Carl Sagan Centre, Mountain View, California, USA
⁷Department of Physics, University of Khartoum, Khartoum, Sudan

This study characterizes carbon and nitrogen abundances and isotopic compositions in ureilitic fragments of Almahata Sitta. Ureilites are carbon-rich (containing up to 7 wt% C) and were formed early in solar system history, thus the origin of carbon in ureilites has significance for the origin of solar system carbon. These samples were collected soon after they fell, so they are among the freshest ureilite samples available and were analyzed using stepped combustion mass spectrometry. They contained 1.2–2.3 wt% carbon; most showed the major carbon release at temperatures of 600–700 °C with peak values of δ13C from −7.3 to +0.4‰, similar to literature values for unbrecciated (“monomict”) ureilites. They also contained a minor low temperature (≤500 °C) component (δ13C = ca −25‰). Bulk nitrogen contents (9.4–27 ppm) resemble those of unbrecciated ureilites, with major releases mostly occurring at 600–750 °C. A significant lower temperature release of nitrogen occurred in all samples. Main release δ15N values of −53 to −94‰ fall within the range reported for diamond separates and acid residues from ureilites, and identify an isotopically primordial nitrogen component. However, they differ from common polymict ureilites which are more nitrogen-rich and isotopically heavier. Thus, although the parent asteroid 2008TC3 was undoubtedly a polymict ureilite breccia, this cannot be deduced from an isotopic study of individual ureilite fragments. The combined main release δ13C and δ15N values do not overlap the fields for carbonaceous or enstatite chondrites, suggesting that carbon in ureilites was not derived from these sources.

Reference
Downes H, Abernethy FAJ, Smith CL, Ross AJ, Verchovsky AB, Grady MM, Jenniskens P, Shaddad MH (2015) Isotopic composition of carbon and nitrogen in ureilitic fragments of the Almahata Sitta Meteorite. Meteoritics and Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12413]
Published by arrangement with John Wiley&Sons