Space Weathering on Meteorite Parent Bodies: Issues Raised by New Lunar Soil Analyses

Details Space Weathering on Meteorite Parent Bodies: Issues Raised by New Lunar Soil Analyses Space Weathering on Meteorite Parent Bodies: Issues Raised by New Lunar Soil Analyses

Jul 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28r.419p&link_type=abstract

Meteoritics, vol. 28, no. 3, volume 28, page 419

Computer Science

Agglutinates, Gaspra, Space Weathering

Scientific paper

The optical properties of lunar soils are different than the rocks from which they are derived. As a consequence of lunar space weathering, soils are darker and exhibit a distinctive red-sloped continuum and weaker mineral absorption bands. The accumulation of dark glass-welded agglutinates has been thought to account for these optical effects of space weathering on lunar soils. Spectroscopic analyses of agglutinate separates and size fractions for a suite of lunar soils indicate that the agglutinate paradigm is insufficient to fully account for lunar optieal alteration [1]. It is the finest fraction of lunar soils (~25 wt%) that dominates the optical properties of the bulk soil. Unlike size fractions of most silicates, for which the finest fraction is the brightest, lunar soil size fractions all have comparable albedos in the short-wavelength visible. In the near-infrared, however, it is the finest fraction that exhibits the steep red continuum and weak absorption bands. The properties of the naturally occurring finest fraction eannot be duplicated by preparing a fine fraction from a larger particle size fraction of mature soil. These results suggest that the optical effects of space weathering on airless bodies is dominated by surface-correlated processes (perhaps associated with the development of fine-grained Fe^o on or near the surface of grains). Furthermore, the accumulation of the larger agglutinates is not necessarily required to account for lunar optical alteration. Recent multispectral images of the asteroid Gaspra obtained with the Galileo SSI camera [2] show spectral variations across the surface. Specifically, several small craters exhibit a higher 0.40/0.56-micrometer ratio (are bluer) and a stronger 1-micrometer absorption strength relative to the surrounding material. Although the spectral differences are small (~10%), this association is highly suggestive of space weathering similar to that occurring on the Moon, but different in magnitude. References: [1] Pieters et al. (1993) JGR, submitted. [2] Belton et al. (1992) Science, 257, 1647.

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