The Chemical Evolution of Chondrite Components: Implications for Mixing in the Solar Nebula

点击翻译按钮获取中文摘要

A crucial period during the history of any solar system is the first ~5 Myr following the ignition of the host star. Within this short time, the solar system transitions from a protoplanetary disk of dust and gas into a organised collection of orbiting planetary bodies. Within our solar system, a large number of meteorites formed during this early time and, as such, can act as a unique window into the processes that occurred during this transitionary period. One class of meteorite - called chondrites - are aggregates of millions of millimetre-sized solids that formed directly from our protoplanetary disk. As such, these meteorites can provide insight into the formation mechanisms and histories of the earliest solids in the solar system, and the processes by which these objects accumulated to form the first asteroid-sized bodies. The isotopic compositions of individual chondrite components (chondrules, refractory inclusions and matrix) suggest that the some of these solids are composed of mixtures of material that originates from different locations within the protoplanetary disk. For example, the titanium isotopic compositions of individual chondrules from carbonaceous chondrites argue that these objects contain remnants of refractory solids that are believed to have formed very close to Sun immediately following its ignition (Gerber et al, 2017). Moreover, the oxygen isotopic composition of the matrix of these meteorites has been used to argue that this component contains material that originates from the far reaches of the solar system (Bryson et al., 2019; under review). Together, these observations support the migration of primitive solids throughout the protoplanetary disk and suggest that the chemical composition of chondrites evolved through the incorporation of these different objects. Because large planetary bodies formed through the agglomeration of numerous asteroid-sized bodies, this migration and mixing could ultimately have played a significant role in generating the chemical composition of the different planetary bodies in our solar system. For instance, the inward flux of distal material has been proposed to be the source of water in hydrated asteroids and possibly the terrestrial planets (Gomes et al, 2005).Such mixing events in the early solar system will have imparted specific chemical signatures onto the individual components of chondrites. Importantly, these signatures will still exist in components that could be mixtures of materials with relatively similar isotopic compositions. As such, detailed measurements of the chemical compositions of individual chondrite components could be used to both explore previously proposed mixing trends as well as potentially identify new mixtures. The aim of this project is to conduct these measurements and use these compositions to constrain the mixing of different reservoirs within the early solar system. The results of these measurements will be used to investigate the extent to which the compositions of different planetary bodies evolved through the addition of material that originates from different regions of the solar system. As such, this project could uncover novel insight into the dynamics of solids throughout the solar system, the addition of dust and gas to the early solar nebula, and the origin and evolution of the chemical composition of a range of planetary bodies.