The titanium isotopic composition of stardust and other meteoritic components

Abstract

Our Solar System is a coagulation of stardust that has been processed and reprocessed by generations of stars. The majority of this stardust, or presolar grains as they are also known, reflects the isotopic compositions of the bulk Solar System, but some presolar grains in meteorites show large deviations from this composition that can only be explained by different nucleosynthetic origins. The isotopic composition of the Solar System is not uniform. Primitive and differentiated meteorites show variations in nucleosynthetic isotope compositions, across many elements, caused by the variable distribution of the presolar grains carrying these anomalies in the material from which meteorites formed. One such element is titanium, which exhibits some of the largest isotopic differences, specifically in ⁴⁶Ti and ⁵⁰Ti. The differences are most prominent between meteorites that formed in the inner Solar System and meteorites that formed in the outer Solar System. However, from previous isotopic studies of presolar grains, no obvious presolar carrier/s which can explain the isotopic variation of Ti in meteorites has been identified by current techniques. Using a novel mass-spectrometer developed at the University of Bristol, we have produced a new technique able to measure Ti isotopes of presolar grains in situ within the host meteorite. The technique has resulted in the discovery of presolar grains that have not been previously identified, such as the most abundant “high-50” grains that possess large positive isotopic anomalies only in the ⁵⁰Ti isotope. The nucleosynthetic origins of the grains within this study are most likely supernovae, both core-collapse and type-1a, which are understood to produce the large abundance of elements in the Solar System around the nuclear statistical peak of iron. Furthermore, there is a large difference in the abundances of “high-50” presolar grains between meteorites from the inner and outer Solar System, which can explain the isotopic variations in bulk Solar System materials. The processes in the early Solar nebula that caused the heterogeneous distribution in presolar grains are debated, but we suggest that the variations were caused by thermal or size discrimination processes that unmixed the presolar grains during the formation of the Solar System.

Date of Award	6 Dec 2022
Original language	English
Awarding Institution	University of Bristol
Supervisor	Tim Elliott (Supervisor) & Ian J Parkinson (Supervisor)