TY - JOUR A1 - Helber, Bernd A1 - Dias, Bruno A1 - Bariselli, Federico A1 - Zavalan, Luiza F. A1 - Pittarello, Lidia A1 - Goderis, Steven A1 - Soens, Bastien A1 - McKibbin, Seann J. A1 - Claeys, Philippe A1 - Magin, Thierry E. T1 - Analysis of meteoroid ablation based on plasma wind-tunnel experiments, surface characterization, and numerical simulations JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - Meteoroids largely disintegrate during their entry into the atmosphere, contributing significantly to the input of cosmic material to Earth. Yet, their atmospheric entry is not well understood. Experimental studies on meteoroid material degradation in high-enthalpy facilities are scarce and when the material is recovered after testing, it rarely provides sufficient quantitative data for the validation of simulation tools. In this work, we investigate the thermochemical degradation mechanism of a meteorite in a high-enthalpy ground facility able to reproduce atmospheric entry conditions. A testing methodology involving measurement techniques previously used for the characterization of thermal protection systems for spacecraft is adapted for the investigation of ablation of alkali basalt (employed here as meteorite analog) and ordinary chondrite samples. Both materials are exposed to a cold-wall stagnation point heat flux of 1.2 MW m(-2). Numerous local pockets that formed on the surface of the samples by the emergence of gas bubbles reveal the frothing phenomenon characteristic of material degradation. Time-resolved optical emission spectroscopy data of ablated species allow us to identify the main radiating atoms and ions of potassium, calcium, magnesium, and iron. Surface temperature measurements provide maximum values of 2280 K for the basalt and 2360 K for the chondrite samples. We also develop a material response model by solving the heat conduction equation and accounting for evaporation and oxidation reaction processes in a 1D Cartesian domain. The simulation results are in good agreement with the data collected during the experiments, highlighting the importance of iron oxidation to the material degradation. KW - meteorites, meteors, meteoroids KW - plasmas KW - techniques: spectroscopic Y1 - 2019 U6 - https://doi.org/10.3847/1538-4357/ab16f0 SN - 0004-637X SN - 1538-4357 VL - 876 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Pittarello, Lidia A1 - Goderis, Steven A1 - Soens, Bastien A1 - McKibbin, Seann J. A1 - Giuli, Gabriele A1 - Bariselli, Federico A1 - Dias, Bruno A1 - Helber, Bernd A1 - Lepore, Giovanni Orazio A1 - Vanhaecke, Frank A1 - Köberl, Christian A1 - Magin, Thierry E. A1 - Claeys, Philippe T1 - Meteoroid atmospheric entry investigated with plasma flow experiments: Petrography and geochemistry of the recovered material JF - Icarus : international journal of solar system studies N2 - 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. KW - Melting experiments KW - Atmospheric entry KW - Meteorites KW - Fusion crust KW - Redox Y1 - 2019 U6 - https://doi.org/10.1016/j.icarus.2019.04.033 SN - 0019-1035 SN - 1090-2643 VL - 331 SP - 170 EP - 178 PB - Elsevier CY - San Diego ER - TY - JOUR A1 - McKibbin, Seann J. A1 - Pittarello, Lidia A1 - Makarona, Christina A1 - Hamann, Christopher A1 - Hecht, Lutz A1 - Chernonozhkin, Stepan M. A1 - Goderis, Steven A1 - Claeys, Philippe T1 - Petrogenesis of main group pallasite meteorites based on relationships among texture, mineralogy, and geochemistry JF - Meteoritics & planetary science : journal of the Meteoritical Society N2 - Main group pallasite meteorites are samples of a single early magmatic planetesimal, dominated by metal and olivine but containing accessory chromite, sulfide, phosphide, phosphates, and rare phosphoran olivine. They represent mixtures of core and mantle materials, but the environment of formation is poorly understood, with a quiescent core-mantle boundary, violent core-mantle mixture, or surface mixture all recently suggested. Here, we review main group pallasite data sets and petrologic characteristics, and present new observations on the low-MnO pallasite Brahin that contains abundant fragmental olivine, but also rounded and angular olivine and potential evidence of sulfide-phosphide liquid immiscibility. A reassessment of the literature shows that low-MnO and high-FeO subgroups preferentially host rounded olivine and low-temperature P2O5-rich phases such as the Mg-phosphate farringtonite and phosphoran olivine. These phases form after metal and silicate reservoirs back-react during decreasing temperature after initial separation, resulting in oxidation of phosphorus and chromium. Farringtonite and phosphoran olivine have not been found in the common subgroup PMG, which are mechanical mixtures of olivine, chromite with moderate Al2O3 contents, primitive solid metal, and evolved liquid metal. Lower concentrations of Mn in olivine of the low-MnO PMG subgroup, and high concentrations of Mn in low-Al2O3 chromites, trace the development and escape of sulfide-rich melt in pallasites and the partially chalcophile behavior for Mn in this environment. Pallasites with rounded olivine indicate that the core-mantle boundary of their planetesimal may not be a simple interface but rather a volume in which interactions between metal, silicate, and other components occur. Y1 - 2019 U6 - https://doi.org/10.1111/maps.13392 SN - 1086-9379 SN - 1945-5100 VL - 54 IS - 11 SP - 2814 EP - 2844 PB - Wiley CY - Hoboken ER -