Amorphous Silicates and Organic Matter within Cometary Interplanetary Dust Particles – Clues to early Solar Nebula Processes

在太阳星云演化的最初一百万年里，发生了诸如凝结、吸积、分化或小行星修饰等复杂的过程。理解这些最初的情节是一项重要但具有挑战性的任务。在这些早期阶段形成的大多数物质随后在太阳系演化过程中被修改或破坏，因此不适合。然而，一些原始的样本，如碳质球粒陨石或彗星尘埃，已经记录了这些主要的太阳星云事件的快照，可以用地球上今天的现代技术来分析，以解开它们复杂的指纹。无定形硅酸盐和有机物是来自彗星的球粒状多孔行星际尘埃粒子的重要组成部分。到目前为止，关于这些颗粒的玻璃状部分及其有机成分的功能化学的化学和物理信息很少。越来越多的证据表明，这两种成分可能在星际介质、太阳星云和陨石/彗星母体中，即分数凝结、离子辐照和流体反应中，对各种过程作出反应。最先进的透射电子显微镜，如麻省理工学院的Themis显微镜或达斯伯里大学的SuperSTEM显微镜，使人们能够以前所未有的规模获得这些极其复杂材料的化学和结构信息。因此，这项提议的重点是研究彗星样本中最原始的成分，即无定形硅酸盐和有机物，目的是解开非常早期的太阳星云或可能的星际过程，如冷凝或流体反应。我们提出的化学研究包括通过STEM-EDX在纳米尺度上获得的主要元素化学，以及通过STEM-EELS获得的这些颗粒的Fe氧化态。此外，通过NanoSIMS对这些IDP进行H-C-N同位素分析将测试IDP成分是否同位素异常。我们还将通过低剂量（60 kV） UltraSTEM EELS研究彗星有机物的功能化学和组成。这些研究将有助于了解在彗星体中形成GEMS颗粒的过程，以及彗星有机物与陨石相比较的分子构成。如果我们了解了这些成分的合成和修饰，我们也将对形成太阳系内较大天体（如彗星、小行星和岩石行星）的原始物质有更广泛的了解。

During the first million years of Solar Nebula evolution, complex processes such as condensation, accretion, differentiation, or asteroidal modification occurred. Understanding these very first episodes is an important, but challenging task. Most materials that formed during these early stages were subsequently modified or destroyed during Solar System evolution and are therefore not suitable. However, some pristine samples such as carbonaceous chondrites or cometary dust have recorded snapshots of these primary solar nebular events, which can be analyzed by modern techniques on Earth today to disentangle their complex fingerprints. Amorphous silicates and organic matter are specifically important components of chondritic-porous interplanetary dust particles derived from comets. Up to now, only little chemical and physical information is available on the glassy fraction of these grains and the functional chemistry of its organic constituents. There is growing evidence that these two components evolve in response to a variety of processes, possibly in the interstellar medium, the Solar Nebula, and on meteorite/cometary parent bodies, i.e., fractional condensation, ion irradiation, and fluid reactions. The most modern transmission electron microscopes, such as the Themis in Münster or the SuperSTEM microscopes in Daresbury, make it possible to obtain chemical and textural information on these extremely complex materials on a scale not previously accessible. The focus of this proposal is therefore to study the most pristine components within cometary samples, i.e., amorphous silicates and organic matter, with the aim to disentangle very early solar nebular or possibly interstellar processes such as condensation or fluid reactions. Our proposed chemical investigations include both the major element chemistry obtained by STEM-EDX on a nanometer scale as well as the Fe oxidation state of these grains by STEM-EELS. Furthermore, H-C-N isotopic analyses of these IDPs by NanoSIMS will test whether IDP constituents are isotopically anomalous. We will also investigate the functional chemistry and constitution of cometary organic matter by low-dose (60 kV) UltraSTEM EELS investigations. These investigations will help to understand the processes that formed GEMS grains in cometary bodies as well as the molecular constitution of cometary organic matter in comparison with their meteoritic counterparts. If we understand the synthesis and modification of these components, we will also gain a broader understanding of the primitive materials that contributed to larger objects within the Solar System such as comets, asteroids, and rocky planets.