In situ experimental formation and growth of Fe nanoparticles and vesicles in lunar soil

1,2Michelle S. Thompson,1Thomas J. Zega,3,4Jane Y. Howe
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12798]
1Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
2NASA Johnson Space Center, Houston, Texas, USA
3Hitachi High-Technologies Canada Inc., Rexdale, Ontario, Canada
4Department of Materials Science and Engineering, University of Toronto, Toronto, Ontario, Canada
Published by arrangement with John Wiley & Sons

We report the results of the first dynamic, in situ heating of lunar soils to simulate micrometeorite impacts on the lunar surface. We performed slow- and rapid-heating experiments inside the transmission electron microscope to understand the chemical and microstructural changes in surface soils resulting from space-weathering processes. Our slow-heating experiments show that the formation of Fe nanoparticles begins at ~575 °C. These nanoparticles also form as a result of rapid-heating experiments, and electron energy-loss spectroscopy measurements indicate the Fe nanoparticles are composed entirely of Fe0, suggesting this simulation accurately mimics micrometeorite space-weathering processes occurring on airless body surfaces. In addition to Fe nanoparticles, rapid-heating experiments also formed vesiculated textures in the samples. Several grains were subjected to repeated thermal shocks, and the measured size distribution and number of Fe nanoparticles evolved with each subsequent heating event. These results provide insight into the formation and growth mechanisms for Fe nanoparticles in space-weathered soils and could provide a new methodology for relative age dating of individual soil grains from within a sample population.

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