This paper reviews some modern applications of the platinum group elements, mainly Ir and Os, in identifying and studying extraterrestrial materials, e.g. study of impact events resulting in biological mass extinctions in the earth's evolution, identification of cosmic dust, tracing of parent body of meteoritic craters on the earth's surface, searching for extrasolar components in the solar system, estimation of fluxes of extraterrestrial matters, etc. Also various representative neutron activation analysis methods developed for these purposes are summarized.