| Popis: |
Meteoroid entry physics remain poorly understood, owing to the extreme conditions experienced by the meteoroid during hypervelocity atmospheric passage, which are not reproducible in ground-test facilities. Therefore, much of our knowledge of fundamental processes is based on bolide lightcurve inference and a posteriori analysis of recovered meteorites. Here, novel in situ microtomography experiments at entry-relevant temperatures were performed on samples of two ordinary chondrites: Tamdakht (H5) and Tenham (L6). The two meteorites were imaged while undergoing a temperature ramp from room temperature to 1200°C. A machine-learning mediated analysis of the microstructural evolution reveals incongruent melting of the meteorite, initiated by the meteoritic iron and iron sulfide grains, and subsequent flow through microcracks that leads to the evolution of large voids. This behavior is correlated to a broad, high-temperature endotherm, noted from differential scanning calorimetry analysis, indicative of the heat of fusion of the melting grains. Correspondingly, a surface elemental analysis indicates that the sulfur species in iron sulfide are highly mobile, which can result in the formation of nonstoichiometric iron–sulfur compounds with melting points that span the temperature range of the observed endotherm. The implications for entry phenomena, in particular meteoroid ablation, are discussed. |
