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Formation Timescales of Amosphous Rims on Lunar Grains Derived from ARTEMIS ObservationsThe weathering of airless bodies exposed to space is a fundamental process in the formation and evolution of planetary surfaces. At the Moon, space weathering induces a variety of physical, chemical, and optical changes including the formation of nanometer-sized amorphous rims on individual lunar grains. These rims are formed by vapor redeposition from micrometeoroid impacts and ion irradiation-induced amorphization of the crystalline matrix. For ion irradiation-induced rims, however, laboratory experiments of the depth and formation timescales of these rims stand in stark disagreement with observations of lunar soil grains. We use observations by the Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) spacecraft in orbit around the Moon to compute the mean ion flux to the lunar surface between 10 eV and 5 MeV and convolve this flux with ion irradiation-induced vacancy production rates as a function of depth calculated using the Stopping Range of Ions in Matter model. By combining these results with laboratory measurements of the critical fluence for charged-particle amorphization in olivine, we can predict the formation timescale of amorphous rims as a function of depth in olivinic grains. This analysis resolves two outstanding issues: (1) the provenance of >100 nm amorphous rims on lunar grains and (2) the nature of the depth-age relationship for amorphous rims on lunar grains.
Document ID
20180002879
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Poppe, A. R. (California Univ. Berkeley, CA, United States)
Farrell, W. M. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Halekas, Jasper S. (Iowa Univ. Iowa City, IA, United States)
Date Acquired
May 16, 2018
Publication Date
January 9, 2018
Publication Information
Publication: Journal of Geophysical Research: Planets
Volume: 123
Issue: 1
ISSN: 2169-9097
Subject Category
Lunar and Planetary Science and Exploration
Report/Patent Number
GSFC-E-DAA-TN55598
Funding Number(s)
CONTRACT_GRANT: NNH10CC04C
Distribution Limits
Public
Copyright
Other
Keywords
Amorphous Rims
Space Weathering