Pd-Ag chronometry of iron meteorites and the accretion and thermal history of differentiated protoplanets

短寿命放射性核素在理解太阳系早期历史方面发挥着关键作用。它们提供了关于几个关键事件的顺序的信息，包括第一批固体凝结的时间尺度以及行星体的吸积和分化。这种年龄限制对于理解行星的形成和限制控制行星体随后演化的参数至关重要。例如，铁陨石的HF-W测年显示，它们的母体在球粒陨石母体之前就已经聚积了很久，这一结果导致了对太阳系早期发展的几乎所有模型的修正。HF-W的结果表明，铁陨石是太阳系内部形成的一些最古老的原行星体的遗迹，因此它们在理解行星形成的最早阶段发挥着关键作用。这项提议旨在对这些分化的原行星的年代学提供新的和坚定的限制。我们将重点研究铁陨石母体的热历史，并旨在利用短寿命的107Pd-107Ag计时器来约束主要岩浆铁组的冷却历史。这项研究的主要预期结果之一将是对其中一些早期分化的原行星的分化和冷却历史进行精细的时间刻度。Pd-Ag同位素研究将与Pd-Ag关闭温度的详细和定量评估相结合。此外，还将精确测定Pd和Ag的初始同位素组成，这两个同位素都没有很好地确定。这种综合方法将对一些最古老的原行星体的大小、内部结构和早期历史提供重要的新限制。

Short-lived radionuclides play a pivotal role in understanding the early history of the solar system. They provide information on the sequence of several key events, including the time-scales of the condensation of the first solids and the accretion and differentiation of planetary bodies. Such age constraints are essential for understanding planet formation and for constraining the parameters that controlled the subsequent evolution of planetary bodies. For example, Hf-W dating of iron meteorites revealed that their parent bodies accreted well before the chondrite parent bodies, a result that has led to revision of almost all models of early solar system development. The Hf-W results demonstrate that iron meteorites are remnants of some of the oldest protoplanetary bodies formed in the inner solar system and as such they play a pivotal role in the understanding of the earliest stage of planet formation. This proposal aims at providing new and firm constraints on the chronology of these differentiated protoplanets. We will focus on the thermal history of iron meteorite parent bodies and aim to constrain the cooling history of the major groups of magmatic irons using the short-lived 107Pd-107Ag chronometer. One of the major expected outcomes of this study will be a refined time scale for the differentiation and cooling history of some of these early-differentiated protoplanets. The Pd-Ag isotopic study will be combined with a detailed and quantitative assessment of the Pd-Ag closure temperature. Furthermore, the initial Pd and Ag isotopic compositions, both of which are not well defined, will be determined precisely. This integrated approach will provide important new constraints on the sizes, internal structure and early history of some of the oldest protoplanetary bodies.