Discovery of Nuclear Tracks in Interplanetary Dust

Nuclear tracks have been identified in interplanetary dust particles (IDP's) collected from the stratosphere. The presence of tracks unambiguously confirms the extraterrestrial nature of IDP's, and the high track densities (10¹⁰ to 10¹¹ per square centimeter) suggest an exposure age of approximately 10⁴ years within the inner solar system. Tracks also provide an upper temperature limit for the heating of IDP's during atmospheric entry, thereby making it possible to distinguish between pristine and thermally modified micrometeorites.