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An Experimental Approach to Understanding the Optical Effects of Space WeatheringThe creation and accumulation of nanophase iron (npFe(sup 0)) is the primary mechanism by which spectra of materials exposed to the space environment incur systematic changes referred to as "space weathering." The optical effects of this npFe(sup 0) on lunar soils are well documented. Space weathering though, should occur on the surface of any planetary body that is not protected by an atmosphere. There is no reason to assume that cumulative space weathering products throughout the solar system will be the same as those found in lunar soils. In fact, these products are likely to be very dependent on the specific environmental conditions under which they were produced. We have prepared a suite of analog soils to explore the optical effects of npFe(sup 0). By varying the size and concentration of npFe(sup 0) in the analogs we found significant systematic changes in the Vis/NIR spectral properties of the materials. Smaller npFe(sup 0) (<10 nm in diameter) dramatically reddens spectra in the visible wavelengths while leaving the infrared region largely unaffected. Larger npFe(sup 0) (>40 nm in diameter) lowers the albedo across the Vis/NIR range with little change in the overall shape of the continuum. Intermediate npFe(sup 0) sizes impact the spectra in a distinct pattern that changes with concentration. The products of these controlled experiments have implications for space-weathered material throughout the inner solar system. Our results indicate that the lunar soil continuum is best modeled by npFe(sup 0) particles with bulk properties in the approx.15-25 nm size range. Larger npFe0 grains result in spectra that are similar in shape to the Mercury continuum. The continuum of S-type asteroid spectra appear to be best represented by small amounts of npFe(sup 0) that is similar to, but slightly smaller on average, than the npFe(sup 0) in lunar soils (approx.10-15 nm).
Document ID
20070019675
Acquisition Source
Johnson Space Center
Document Type
Preprint (Draft being sent to journal)
Authors
Noble, Sarah K. (NASA Johnson Space Center Houston, TX, United States)
Keller, Lindsay P. (NASA Johnson Space Center Houston, TX, United States)
Pieters, Carle M. (Brown Univ. Providence, RI, United States)
Date Acquired
August 23, 2013
Publication Date
January 1, 2007
Subject Category
Space Sciences (General)
Funding Number(s)
CONTRACT_GRANT: NAG5-11763
CONTRACT_GRANT: NAG5-13609
CONTRACT_GRANT: NGT9-66
PROJECT: RTOP 344-31-40-07
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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