On the presolar origin of the “normal planetary” noble gas component in meteorites

Abstract

Several components of planetary noble gases, including CCFXe (Xe‐X), s‐process Kr and Xe, and Ne‐E, are now thought to have had a presolar origin. We propose that the “normal planetary” noble gas component, which contains most of the planetary Ar, Kr, and Xe, is also presolar. This component was trapped in carbonaceous mantles as the mantles formed on grain surfaces in the molecular cloud. The presolar dust grains and their carbonaceous mantles were then incorporated into primitive meteorites. This model naturally explains: (1) the affinity of “normal planetary” noble gases for carbonaceous material in primitive chondrites; (2) the near absence of He and Ne in the “normal planetary” component; (3) the elemental fractionation patterns of the “exotic” and “normal planetary” components; (4) the similarity of the isotopic compositions of “normal planetary” and trapped solar Ar, Kr, and Xe; (5) the high noble gas content of the “normal planetary” gas carrier; (6) several aspects of the chemistry of the “normal planetary” gas carrier; (7) the correlation of planetary noble gases with the fine‐grained material in primitive chondrites; and (8) the widespread occurrence of the planetary fractionation pattern throughout the solar system.