@article{PittarelloGoderisSoensetal.2019, author = {Pittarello, Lidia and Goderis, Steven and Soens, Bastien and McKibbin, Seann J. and Giuli, Gabriele and Bariselli, Federico and Dias, Bruno and Helber, Bernd and Lepore, Giovanni Orazio and Vanhaecke, Frank and K{\"o}berl, Christian and Magin, Thierry E. and Claeys, Philippe}, title = {Meteoroid atmospheric entry investigated with plasma flow experiments: Petrography and geochemistry of the recovered material}, series = {Icarus : international journal of solar system studies}, volume = {331}, journal = {Icarus : international journal of solar system studies}, publisher = {Elsevier}, address = {San Diego}, issn = {0019-1035}, doi = {10.1016/j.icarus.2019.04.033}, pages = {170 -- 178}, year = {2019}, abstract = {Melting experiments attempting to reproduce some of the processes affecting asteroidal and cometary material during atmospheric entry have been performed in a high enthalpy facility. For the first time with the specific experimental setup, the resulting material has been recovered, studied, and compared with natural analogues, focusing on the thermal and redox reactions triggered by interaction between the melt and the atmospheric gases under high temperature and low pressure conditions. Experimental conditions were tested across a range of parameters, such as heat flux, experiment duration, and pressure, using two types of sample holders materials, namely cork and graphite. A basalt served as asteroidal analog and to calibrate the experiments, before melting a H5 ordinary chondrite meteorite. The quenched melt recovered after the experiments has been analyzed by mu-XRF, EDS-SEM, EMPA, LA-ICP-MS, and XANES spectroscopy. The glass formed from the basalt is fairly homogeneous, depleted in highly volatile elements (e.g., Na, K), relatively enriched in moderately siderophile elements (e.g., Co, Ni), and has reached an equilibrium redox state with a lower Fe3+/Fe-tot ratio than that in the starting material. Spherical objects, enriched in SiO2, Na2O and K2O, were observed, inferring condensation from the vaporized material. Despite instantaneous quenching, the melt formed from the ordinary chondrite shows extensive crystallization of mostly olivine and magnetite, the latter indicative of oxygen fugacity compatible with presence of both Fe2+ and Fe3+. Similar features have been observed in natural meteorite fusion crusts and in micrometeorites, implying that, at least in terms of maximum temperature reached and chemical reactions, the experiments have successfully reproduced the conditions likely encountered by extraterrestrial material following atmospheric entry.}, language = {en} } @article{QuiricoMorozSchmittetal.2016, author = {Quirico, E. and Moroz, Liubov V. and Schmitt, B. and Arnold, Gabriele and Faure, M. and Beck, P. and Bonal, L. and Ciarniello, M. and Capaccioni, F. and Filacchione, G. and Erard, S. and Leyrat, C. and Bockelee-Morvan, D. and Zinzi, A. and Palomba, E. and Drossart, P. and Tosi, F. and Capria, M. T. and De Sanctis, M. C. and Raponi, A. and Fonti, S. and Mancarella, F. and Orofino, V. and Barucci, A. and Blecka, M. I. and Carlson, R. and Despan, D. and Faure, A. and Fornasier, S. and Gudipati, M. S. and Longobardo, A. and Markus, K. and Mennella, V. and Merlin, F. and Piccioni, G. and Rousseau, B. and Taylor, F.}, title = {Refractory and semi-volatile organics at the surface of comet 67P/Churyumov-Gerasimenko: Insights from the VIRTIS/Rosetta imaging spectrometer}, series = {Icarus : international journal of solar system studies}, volume = {272}, journal = {Icarus : international journal of solar system studies}, publisher = {Elsevier}, address = {San Diego}, organization = {Rosetta VIRTIS Team}, issn = {0019-1035}, doi = {10.1016/j.icarus.2016.02.028}, pages = {32 -- 47}, year = {2016}, abstract = {The VIRTIS (Visible, Infrared and Thermal Imaging Spectrometer) instrument aboard the Rosetta spacecraft has performed extensive spectral mapping of the surface of comet 67P/Churyumov-Gerasimenko in the range 0.3-5 mu m. The reflectance spectra collected across the surface display a low reflectance factor over the whole spectral range, two spectral slopes in the visible and near-infrared ranges and a broad absorption band centered at 3.2 mu m. The first two of these characteristics are typical of dark small bodies of the Solar System and are difficult to interpret in terms of composition. Moreover, solar wind irradiation may modify the structure and composition of surface materials and there is no unequivocal interpretation of these spectra devoid of vibrational bands. To circumvent these problems, we consider the composition of cometary grains analyzed in the laboratory to constrain the nature of the cometary materials and consider results on surface rejuvenation and solar wind processing provided by the OSIRIS and ROSINA instruments, respectively. Our results lead to five main conclusions: (i) The low albedo of comet 67P/CG is accounted for by a dark refractory polyaromatic carbonaceous component mixed with opaque minerals. VIRTIS data do not provide direct insights into the nature of these opaque minerals. However, according to the composition of cometary grains analyzed in the laboratory, we infer that they consist of Fe-Ni alloys and FeS sulfides. (ii) A semi-volatile component, consisting of a complex mix of low weight molecular species not volatilized at T similar to 220 K, is likely a major carrier of the 3.2 p.m band. Water ice contributes significantly to this feature in the neck region but not in other regions of the comet. COOH in carboxylic acids is the only chemical group that encompasses the broad width of this feature. It appears as a highly plausible candidate along with the NH4+ ion. (iii) Photolytic/thermal residues, produced in the laboratory from interstellar ice analogs, are potentially good spectral analogs. (iv) No hydrated minerals were identified and our data support the lack of genetic links with the CI, CR and CM primitive chondrites. This concerns in particular the Orgueil chondrite, previously suspected to have been of cometary origin. (v) The comparison between fresh and aged terrains revealed no effect of solar wind irradiation on the 3.2 mu m band. This is consistent with the presence of efficient resurfacing processes such as dust transport from the interior to the surface, as revealed by the OSIRIS camera. (C) 2016 Elsevier Inc. All rights reserved.}, language = {en} }