^1,2N. van Roosbroek, ²L. Pittarello, ³A. Greshake,¹V. Debaille,²P. Claeys
¹Laboratoire G-Time, Université Libre de Bruxelles, Brussels, Belgium
²Analytical, Environmental, and Geo-Chemistry (AMGC), Vrije Universiteit Brussel, Brussels, Belgium
³Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany

About half of the IIE nonmagmatic iron meteorites contain silicate inclusions with a primitive to differentiated nature. The presence of preserved chondrules has been reported for two IIE meteorites so far, Netschaëvo and Mont Dieu, which represent the most primitive silicate material within this group. In this study, silicate inclusions from two samples of Netschaëvo were examined. Both silicate inclusions are characterized by a porphyritic texture dominated by clusters of coarse-grained olivine and pyroxene, set in a fine-grained groundmass that consists of new crystals of olivine and a glassy appearing matrix. This texture does not correspond to the description of the previously examined pieces of Netschaëvo, which consist of primitive chondrule-bearing angular clasts. Detailed petrographic observations and geochemical analyses suggest that the investigated samples of Netschaëvo consist of quenched impact melt. This implies that Netschaëvo is a breccia containing metamorphosed and impact-melt rock (IMR) clasts and that collisions played a major role in the formation of the IIE group.

Reference
van Roosbroek N, Pittarello L, Greshake A, Debaille V, Claeys P (2016) First finding of impact melt in the IIE Netschaëvo meteorite. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12596]
Published by arrangement with John Wiley&Sons

¹Yoshitaka HOMMA, ²Yui KOUKETSU, ¹Hiroyuki KAGI, ³Takashi MIKOUCHI, ⁴Hikaru YABUTA
¹Geochemical Research Center, Graduate School of Science, The University of Tokyo
²Department of Earth and Planetary Science, Graduate School of Environmental Studies, Nagoya University
³Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo
⁴Department of Earth and Space Science, Graduate School of Science, Osaka University

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

HOMMA Y, KOUKETSU Y, KAGI H, MIKOUCHI T, YABUTA H (2015) Raman spectroscopic thermometry of carbonaceous material in chondrites: four–band fitting analysis and expansion of lower temperature limit. Journal of Mineralogical and Petrological Sciences 110, 276-282
Link to Article [http://doi.org/10.2465/jmps.150713a]

¹Zoe A. Landsman, ^2,3Javier Licandro, ¹Humberto Campins, ⁴Julie Ziffer, ⁵Mario de Prá, ⁶Dale P. Cruikshank
¹Department of Physics, University of Central Florida, 4111 Libra Drive, PS 430, Orlando, FL 32826, United States
²Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
³Departamento de Astrofísica, Universidad de La Laguna, E-38205 La Laguna, Tenerife, Spain
⁴Department of Physics, University of Southern Maine, 96 Falmouth St, Portland, ME 04103, United States
⁵Observatório Nacional, R. General José Cristino, 77 – Imperial de São Cristóvão, Rio de Janeiro – RJ, 20921-400, Brazil
⁶NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035, United States

Spectroscopic investigations of primitive asteroid families constrain family evolution and composition and conditions in the solar nebula, and reveal information about past and present distributions of volatiles in the solar system. Visible and near-infrared studies of primitive asteroid families have shown spectral diversity between and within families. Here, we aim to better understand the composition and physical properties of two primitive families with vastly different ages: ancient Themis ( ∼ 2.5 Gyr) and young Veritas ( ∼ 8 Myr). We analyzed the 5 – 14μm Spitzer Space Telescope spectra of 11 Themis-family asteroids, including eight previously studied by Licandro et al. (2012), and nine Veritas-family asteroids, for a total of 20 asteroids in our sample. We detect a broad 10-μm emission feature, attributed to fine-grained and/or porous silicate regolith, in all 11 Themis-family spectra and six of nine Veritas-family asteroids, with 10-μm spectral contrast ranging from 1% ± 0.1% to 8.5% ± 0.9%. We used thermal modeling to derive diameters, beaming parameters and albedos for our sample. Asteroids in both families have beaming parameters near unity and geometric albedos in the range 0.03 – 0.14. Spectral contrast of the 10-μm silicate emission feature is correlated with beaming parameter and rotation period in the Themis family, and may be related to near-infrared spectral slope for both families. We see no correlations of 10-μm emission with diameter or albedo for either family. Comparison with laboratory spectra of primitive meteorites suggests these asteroids are similar to meteorites with relatively low abundances of phyllosilicates. Overall, our results suggest the Themis and Veritas families are primitive asteroids with variation in composition and/or regolith properties within both families.

Reference
Landsman ZA, Licandro J, Campins H, Ziffer J, Prá M, Cruikshank DP (2016)
The Veritas and Themis asteroid families: 5–14 μm spectra with the Spitzer Space Telescope. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.01.008]
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