Crystal Morphology of Antarctic Micrometeorites Based on Melting–Cooling Processes During Atmospheric Entry

Micrometeorites (MMs), which are cosmic dust grains ranging from 10 microns to 2 mm in size, can reach the Earth’s surface through collisions with asteroids or by fragmentation of comets in space. When MMs enter the atmosphere, they are heated to varying degrees depending on their size, mass, speed, and angle of entry. As a result of friction during atmospheric entry, MMs undergo partial melting and subsequently recrystallize during undercooling. In this study, we focused on molten micrometeorites and identified four main types: silicate, glassy, ferruginous, and intermediate forms. The mineralogical compositions of MMs were determined using Raman spectroscopy, while their chemical compositions and phase changes were analyzed using SEM-EDX and LA-ICP-MS methods. The primary silicate phases include olivine, pyroxene, and plagioclase, whereas the opaque mineral phases comprise magnetite, troilite, and kamacite (Fe-Ni alloys). Olivine exhibits Fo values ranging from 41 to 96 mol%, and the pyroxenes consist of enstatite and pigeonite compositions (Wo3–8En79–97Fs2–19). Olivine and magnetite display dendritic and skeletal crystal morphologies due to melting and undercooling during atmospheric entry.