Solar-wind derived light noble gases in micrometeorites collected at the Dome Fuji Station: Characterization by stepped pyrolysis

摘要

Noble gases in micrometeorite-bearing particles were characterized by the total-melting and stepped-heating analyses, in order to determine average compositions of light noble gases of micrometeorites collected at the Dome Fuji Station. He and Ne are dominated by solar-wind derived noble gases and the concentrations are comparable to the highest ones detected so far in carbonaceous chondrites. Cosmogenic gases are a very minor component in micrometeorites, suggesting short exposure to solar and galactic cosmic rays. The high ratio of solar to cosmogenic gases suggests that the micrometeorites had been small particles in the interplanetary space to have large surface areas to be exposed to solar winds. The micrometeorites are supposed to have fallen on Antarctica in the recent fifty years with snow around the Dome Fuji Station (T. Nakamura et al., Antarct. Meteorite Res., 12,183,1999a), and hence they are particles generated in the modern solar system and came to the Earth after short periods of exposure to solar winds and galactic cosmic rays.