High-temperature events in the protoplanetary disk: Formation conditions of chondrules and refractory inclusions

球粒陨石包含了太阳系形成的古老记录。陨石的两个重要组成部分，球粒和耐火包裹体，在太阳系历史的最早阶段形成于原行星盘环境。球粒和一些耐火夹杂物经历了短暂的高温加热事件，导致熔融，然后迅速冷却。热历史是从天然样品的化学和同位素研究，以及模拟成分的实验室研究中解释的：典型的峰值温度约为1500 ℃，典型的冷却速率在每小时几十到几百度的范围内。尽管很明显这些高温事件影响了大量的盘状物质，但关于加热机制仍有很多争论。存在几种不同的模型，包括来自原太阳的直接辐射加热，在盘内的各种设置中产生的激波前沿加热，以及微行星之间的碰撞。为了完善和评估不同的模型，我们需要确定来自球粒和耐火夹杂物本身的加热过程的鲁棒约束。对太阳系外行星和原行星盘（如HL金牛座）的新天文观测（见下文）给了我们对行星系统形成的令人兴奋的新见解，对陨石的研究提供了这些环境的直接样本。本博士项目将联合收割机对陨石中球粒和耐火夹杂物的观测与旨在再现纹理、矿物组合、矿物成分和同位素效应的实验研究相结合。我们的目标是确定约束的chondruleformingmechanism，可用作输入参数的球粒形成模型。以前的实验对加热过程有广泛的限制，但仍然有许多未解的问题。从亚毫米尺度的观测中，我们可以对数千公里尺度的过程进行推断（见图）。实验将在可编程温度控制的单气氛炉中进行。对天然样品和实验运行产品的研究将使用微束分析技术，包括扫描电子显微镜、电子微探针分析、拉曼光谱和二次离子质谱。

Chondrite meteorites contain an ancient record of the formation of the solar system. Two importantcomponents of chondrites, chondrules and refractory inclusions, were formed in the protoplanetarydisk environment in the earliest stages of solar system history. Chondrules and some refractoryinclusions underwent brief high-temperature heating episodes that resulted in melting followed byrapid cooling. Thermal histories are interpreted from chemical and isotopic studies of naturalsamples, as well as laboratory studies of analog compositions: typical peak temperatures are around1500 C and typical cooling rates are in the range of tens to hundreds of degrees per hour. Eventhough it is clear that these high-temperature events affected large volumes of disk material, thereis much debate about the heating mechanism. Several different models exist, including heating bydirect radiation from the protosun, heating in shock fronts produced in a variety of settings withinthe disk, and impacts between planetesimals. In order to refine and assess the different models, weneed to determine robust constraints on the heating process from chondrules and refractoryinclusions themselves. New astronomical observations of extrasolar planets and protoplanetarydisks such as HLTauri (see reference below) are giving us exciting new insights into the formation ofplanetary systems, and studies of chondrites provide direct samples of these environments.This PhD project will combine observations of chondrules and refractory inclusions in chondriteswith experimental studies designed to reproduce textures, mineral assemblages, mineralcompositions and isotopic effects. The objective is to determine constraints on the chondruleformingmechanism that can be used as input parameters for chondrule formation models. Previousexperiments have placed broad constraints on the heating process, but there are still manyunanswered questions. From observations at the sub-millimetre scale, we can make inferencesabout processes that operated on a scale of thousands of kilometres (see figure). Experiments willbe carried out in a one-atmosphere furnace with programmable temperature control. Studies of natural samples and experimental run products will use microbeam analytical techniques includingscanning electron microscopy, electron microprobe analysis, Raman spectroscopy and secondary ionmass spectrometry.