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Published 1979 | Published
Book Section - Chapter Open

Isotopic Heterogeneities in the Solar System


The nature of isotopic anomalies in solar system material is discussed with emphasis on correlated anomalies in refractory elements. Evidence for the existence of short-lived radioactive nuclides in the early solar system is given and is used to estimate the time scale for the last injection of freshly synthesized nuclear material. It is shown that the early solar nebula was incompletely mixed and contained debris which was injected from a stellar source at most a few million years prior to the formation of the solar system. It appears that the average solar system material is made up of ambient interstellar material which was deficient in certain nuclear species to which was added a small fraction of freshly synthesized material. It is this mixture which now makes up the bulk solar system. At the present time there may still remain both substantial and subtle isotopic differences between the sun, the terrestrial planets, and volatile-rich planetary bodies including comets. The isotopic variations which are observed reflect slightly different proportions of nuclei from different stellar sources which were locally well mixed and homogenized prior to or during the formation of the early solar nebula condensates. The process of local homogenization apparently destroyed most pre-solar dust grains but preserved the distinctive average isotopic character of the local regions. Substantial isotopic differences existed between the cool gas and some condensed matter. This is manifest in major chemical and some associated isotopic alteration of the early condensates.

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© 1979 Universite de Liege. This work was supported by grants from the National Science Foundation and the National Aeronautics and Space Administration. Without this ongoing support the precise data summarized in this work could not have been obtained. The contributions of Malcom McCulloch to part of the data summarized here merit special mention. Discussion with and stimulation from our colleagues in the Kellogg Radiation Laboratory is gratefully acknowledged. In this report we have omitted a general discussion of the rare gases and, in particular, xenon and krypton anomalies. These observations and ideas are of great importance and have been the subject of extensive investigation and discussion over the past two decades. It is hoped that our noble colleagues with affection for atomic numbers 36-10-54 will recognize the limited nature of this report.

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