Earth Planets Space, Vol. 54 (No. 12), pp. e5-e7, 2002E-LETTER
Erika Kurahashi1, Chihiro Yamanaka2, Keiko Nakamura3, and Sho Sasaki1
1Department of Earth and Planetary Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
2Department of Earth and Space Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
3Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501, Japan
(Received July 19, 2002; Revised November 8, 2002; Accepted November 14, 2002)
S-type asteroids are believed to be parent bodies of ordinary chondrites. However, the reflectancespectra of S-type asteroids are different from those of ordinary chondrites. This spectral mismatch is strongly considered as a result of space weathering, where high-velocity dust particle impacts should change the optical properties of the uppermost regolith surface of asteroids. To simulate space weathering by impact heating of dust particles, we irradiated nanosecond pulse laser beam onto planetary surface materials, whose pulse duration and energy rate are comparable with those of real dust impacts. The laser-irradiated samples show optical changes similar to that by space weathering, and contain nanophase metallic iron particles considered as the essential cause of space weathering. After laser-irradiations, we observed the samples by an Electron Spin Resonance (ESR) to perform quantitative analysis of nanophase metallic iron particles. We report the first description that the quantities of nanophase metallic iron particles in olivine samples increase at higher space weathering degree.
key words: Space weathering, electron spin resonance, nanophase metallic iron, laser irradiation, reflectance change.