SEARCHING FOR EVIDENCE OF ATMOSPHERIC ENTRY HEATING IN A COLLECTION OF ANTARCTIC MICROMETEORITES

Micrometeorites (MMs) represent a distinct collection of cosmic dust (micrometre-sized extra-terrestrial grains) with a typical size range of 100-200 µm. MMs are thought to be derived primarily from asteroidal material (Genge et al., 1997), compared to interplanetary dust particles (IDPs), which are usually smaller (5-50 µm) and contain cometary-derived material (Bradley, 1994). While these collections are different, they both experience similar processes related to their interaction with the atmosphere. Any differences observed between these materials may therefore have important implications for the processes affecting cosmic dust on atmospheric entry. Previous studies have suggested metrics for atmospheric entry heating, including sulphur (S) and zinc (Zn) depletions and the presence of magnetite rims (e.g., Greshake et al., 1998). Studying MMs in detail may thus help to determine the extent of heating of these materials.

Here, we present the analysis of 10 particles from a collection of over 65 MMs from Cap Prud’homme, Antarctica, recovered in 1994 (Maurette et al., 1992). Backscattered electron (BSE) imaging with a field emission-scanning electron microscope (FE-SEM) reveals distinct compositional layers, with energy-dispersive spectroscopy (EDS) giving qualitative elemental distributions. Some particles show distinct core and rim regions, with EDS data highlighting possible partitioning of elements between these areas, particularly in iron (Fe) and oxygen (O). Particles show spatial variations in texture: fractures and porous regions are present within some core regions, whilst bubbly textures are observed on the outer rim of other particles, similar to textures seen in some meteorite fusion crusts. Three particles show localised elemental ‘hotspots’, in silicon (Si), aluminium (Al) and Fe. With further analyses on selected regions of interest (ROI) up to nanometre scales, we plan to better characterise elemental distributions within these materials. This may reveal 3D chemical trends previously unseen at lower resolutions.

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