Earth, Planets and Space

, Volume 53, Issue 11, pp 1071–1075 | Cite as

The mystery of 506.5 nm feature of reflectance spectra of Vesta and Vestoids: Evidence for space weathering?

  • Takahiro Hiroi
  • Carlé M Pieters
  • Faith Vilas
  • Sho Sasaki
  • Yoshimi Hamabe
  • Erika Kurahashi
Open Access
Article

Abstract

Although asteroid 4 Vesta and Vestoids have been believed to be the source of a group of basaltic meteorites called HEDs, there have been detailed spectral analyses on the spectral redness and the 506.5 nm absorption band, suggesting controversy on their space weathering processes and origins. In order to evaluate a possibility that such an apparent inconsistency may be explained by the space weathering, the 506.5 nm spectral feature and reddening trend are examined for Vesta and Vestoids, HED meteorites, lunar soils, and laser irradiated pyroxene samples in this paper. Our results indicate that all fresh HED meteorites have the 506.5 nm band at different wavelengths according to their classes, lunar soils seem to lose the 506.5 nm band as they mature, and pulse laser irradiation on the pyroxene sample seems to reduce the 506.5 nm band. Therefore, absence of the 506.5 nm band on some Vestoids can be due to space weathering although the relationship between the visible redness and presence/absence of the 506.5 nm band of Vesta and Vestoids is inconsistent with the assumed HED-lunar space weathering trend based on the above laboratory results. Other possible explanations are that some Vestoids experienced shock heavy enough to erase the 506.5 nm band and that pyroxenes on some Vestoids are not similar to those in HED meteorites. Even if the latter case is true and some Vestoids are not made of HED materials, HED meteorites could still come from Vesta unless we assume all Vestoids have to be fragments of Vesta.

Keywords

Space Weathering Pulse Laser Irradiation Lunar Soil Lunar Planet Lunar Sample 

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Copyright information

© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. 2001

Authors and Affiliations

  • Takahiro Hiroi
    • 1
  • Carlé M Pieters
    • 1
  • Faith Vilas
    • 2
  • Sho Sasaki
    • 3
  • Yoshimi Hamabe
    • 3
  • Erika Kurahashi
    • 3
  1. 1.Department of Geological SciencesBrown UniversityProvidenceUSA
  2. 2.SN3NASA Johnson Space CenterHoustonUSA
  3. 3.Department of Earth and Planetary ScienceThe University of TokyoTokyoJapan

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