Unlocking the isotopic evolution of the early Solar System: evidence from chondrules

Solar systems, including our own, form from the collapse of clouds of dust and gas which has been processed by previous generations of stars. This collapsing cloud, the ‘early Solar System’, set the stage for the subsequent formation and evolution of the collection of planets and asteroids we know today. We can examine the sources and processes of the early Solar System, e.g. inner Solar System volatile delivery, by looking at variations in the isotope compositions between different meteorites. These variations result from incomplete mixing of material from different stellar sources. Stars produce elements, and their isotopes, in dramatically different abundances and release them during their last stages of evolution (e.g. supernovae). Meteorites formed in the early Solar System and sampled these different pre-solar signatures to varying degrees. Therefore, by measuring the isotopic compositions of materials from the early Solar System we can trace the mixing of material during the collapse of the cloud of dust and gas.
 
Over the past 20 years the isotopic variations of a wide range of elements have been measured in meteorites. This has painted a picture of characteristic isotope compositions for the inner and outer Solar System. Using these isotopic variations, the origins of meteorites can be classified and their relationships examined. However, despite the apparent systematic patterns in these isotopic variations their origin remains uncertain. Recently, several models have been proposed to explain how these variations were produced.  In one family of models, the systematic differences between the inner and outer Solar System were inherited from stratification in the parent molecular cloud. In another set of models, the different stellar sources were progressively unmixed (e.g. by thermal processes) from a previously physically homogeneous parent molecular cloud. These two models predict similar isotopic variations through the resulting Solar System...