Insights into the early Solar System: Ba isotope composition of meteorites and their components

Date & time

4–5pm 17 January 2013

Location

Jaeger Seminar Room, 1st Floor Jaeger 1 RSES

Speakers

Katherine R. Bermingham, University of Maryland

Event series

The origin and degree of isotopic heterogeneity in the early Solar System is a major unknown in planetary science. In this study, the distribution of Ba isotopes in refractory inclusions and whole rock meteorites (eucrites, diogenites, ordinary chondrites, Martian meteorites, enstatite chondrites and carbonaceous chondrites) was determined to constrain the levels of Ba isotope heterogeneity in the Solar System. Our results show that Ba isotopes, and thus their carrier phases, were homogeneously distributed throughout the feeding zones for all meteorite types analyzed. Moreover, there appears to be a correlation among the number of nucleosynthetic processes that contributed to an element, the relative contribution of the different nucleosynthetic processes to a specific element, and the presence of nucleosynthetic isotopic anomalies in bulk meteorite samples. The observation that some elements show homogeneous and others heterogeneous isotope distribution on the regional scale, therefore, may be in part due to the nucleosynthetic processes that produced these isotopes and the mixing rates of the different elements into the disk. Three of the studied Allende CAIs display excesses 135Ba that are not accompanied by 137Ba anomalies, the absence of which is here interpreted to indicate that the 135Ba anomaly is not nucleosynthetic in origin but rather developed from the decay of short-lived 135Cs. It is unlikely that this contribution to 135Ba occurred via in situ decay of live 135Cs because there is no correlation between 135Ba excess and a superchondritic Cs/Ba. Rather, it may be evidence that a transient, high Cs/Ba (> CI) reservoir existed in the early Solar System when 135Cs was extant and some early condensates record the former presence of live 135Cs as a 135Ba excess.

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