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

在任何太阳系的历史中，一个关键时期是主恒星着火后的第一个~ 5myr。在这么短的时间内，太阳系从一个由尘埃和气体组成的原行星盘转变为一个有组织的轨道行星体的集合。在我们的太阳系中，大量的陨石形成于这个早期时期，因此，可以作为一个独特的窗口，了解在这个过渡时期发生的过程。其中一类陨石——球粒陨石——是由数百万毫米大小的固体组成的集合体，直接形成于我们的原行星盘。因此，这些陨石可以让我们深入了解太阳系最早固体的形成机制和历史，以及这些物体积聚形成第一个小行星大小的天体的过程。单个球粒陨石成分（球粒、难熔包裹体和基质）的同位素组成表明，其中一些固体是由来自原行星盘中不同位置的物质混合物组成的。例如，来自碳质球粒陨石的单个球粒的钛同位素组成认为，这些物体含有耐火固体的残留物，据信这些固体是在太阳着火后非常靠近太阳的地方立即形成的（Gerber et al, 2017）。此外，这些陨石基质的氧同位素组成已被用来证明该成分含有来自太阳系远端的物质（Bryson et al., 2019；正在审查中）。总之，这些观测结果支持原始固体在原行星盘中的迁移，并表明球粒陨石的化学成分是通过这些不同物体的结合而进化的。由于大型行星体是由许多小行星大小的天体聚集形成的，因此这种迁移和混合最终可能在形成太阳系中不同行星体的化学成分方面发挥了重要作用。例如，有人提出，远端物质向内流动是含水小行星的水源，也可能是类地行星的水源（Gomes et al, 2005）。早期太阳系的这种混合事件将赋予球粒陨石的各个组成部分特定的化学特征。重要的是，这些特征仍然存在于同位素组成相对相似的材料混合物中。因此，对单个球粒陨石组成的化学成分的详细测量可以用来探索先前提出的混合趋势，也可以用来潜在地识别新的混合物。这个项目的目的是进行这些测量，并利用这些成分来限制早期太阳系中不同储层的混合。这些测量的结果将用于研究不同行星体的组成在多大程度上是通过添加来自太阳系不同区域的物质而演变的。因此，这个项目可以揭示对整个太阳系固体动力学的新见解，早期太阳星云中尘埃和气体的添加，以及一系列行星体化学成分的起源和演化。

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.