240-11 Iron Whiskers Associated with Micrometeoroid Impact Craters on Lunar Ilmenite

Session: From Atoms to Asteroids and Habitable Planets: Coordinated Analysis of Planetary Samples and Their Terrestrial Analogues

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Abstract:

The total flux of solar system meteoroids is dominated by objects less than 1 mm in diameter whose impact effects play a major role in modifying the surfaces of airless bodies. A portion of this alteration is simple grain size reduction through mechanical fracturing, but many small-scale impact events are driven by micrometeoroids traveling at speeds fast enough to locally melt and vaporize the target materials. Metallic iron nanoparticles are a well-known constituent of lunar regolith and are a product of impact melting and/or solar wind ion irradiation of Fe-bearing minerals on the Moon. These Fe nanoparticles range from less than 5 nm in diameter up to a few hundred nanometers in diameter and play a major role in the optical properties of the lunar surface. Metallic iron whiskers have been observed growing on the surfaces of iron sulfides from the Moon and asteroid Itokawa. These whisker structures are quite different from the Fe nanoparticles; nevertheless, their characteristics strongly link them to surface alteration processes like space weathering, the broader term encompassing agents like micrometeoroid impacts and solar wind ion irradiation. Recent experimental work has more specifically linked metallic Fe whisker development to micrometeoroid impact of sulfides. We previously reported metallic Fe whiskers erupting from the wall of a 15-µm crater on the surface of an ilmenite grain in lunar rock 71055. This finding supports the experimental work done on sulfides, but additional data is required to further validate and constrain the nature of this process. Here, we have performed electron energy loss spectroscopy spectrum imaging (EELS-SI) on the interface of Fe whiskers in the crater we previously described to detail the distribution of different oxidation states of Fe. We also will share data on additional ilmenite microcraters to provide further insight on how Fe whisker development may vary with respect to crater size and other relevant properties.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7806

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