Stable Isotope Studies of Meteorites with Applications to Terrestrial Planet Formation and Evolution

Author(s): Jordan, Michelle | Advisor(s): Young, Edward D | Abstract: Stable isotopes serve as tracers of processes. Through analysis of the stable isotope compositions of meteorites, we can look back in time and learn about the conditions present in our nascent Solar System as well as the processes that were occurring. Here we characterize aspects of terrestrial planet formation and evolution using stable isotopes as our tool.To understand how the first rocky material in our Solar System formed, we measure the isotopic compositions of several major rock-forming elements in the oldest surviving solids that formed in the Solar System (calcium-aluminum-rich inclusions). Measurements of 25Mg, 29Si, 44Ca, 49Ti, and anomalous 50Ti in these refractory inclusions indicate that CAIs are not primary condensates, but instead, aggregates of pre-existing materials. Furthermore, they display signs of heterogeneity, which are echoes of larger scale heterogeneity that existed in the precursor material from which they formed. The compositions of CAIs are consistent with averaging of the precursor material; this averaging has the effect of dampening the heterogeneity exhibited by the precursor material. We also use stable isotopes to understand the nature of core formation in planetesimals. Measurements of the iron isotopic composition, 57Fe, of differentiated aubrite, iron, and chondrite meteorites allow us to form a more complete picture of core formation. The 57Fe of the metal and silicate phases in aubrite meteorites indicate that the metallic phase is enriched in 57Fe/54Fe. The magnitude of this fractionation cannot explain the observed difference in the compositions of iron meteorites and chondrites. Instead, the elevated 57Fe/54Fe of iron meteorites relative to chondrites, is likely due to evaporation and not core-mantle differentiation.