Gravoturbulent Planetesimal Formation in the Early Solar System

早期太阳系中的重力湍流小行星形成

• 批准号: 146496795
• 负责人: Professor Dr. H. Hubertus Klahr
• 金额: --
• 依托单位: Max-Planck-Institut für Astronomie (MPIA)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2010
• 资助国家: 德国
• 起止时间: 2009-12-31 至 2017-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/146496795?language=en
• 关键词: Gravoturbulent; Planetesimal; Formation; Early; Solar

We investigate the formation of planetesimals from a gravitationally unstable cloud of chondrules and matrix material embedded in the early solar nebula. The planetesimal precursor material (chondrules or chondrule-sized grains plus matrix material) evolves due to coagulation, fragmentation, and drift in the early solar nebula. In our project we connect predictions on the abundance of precursor material to the composition of primitive chondrites in the framework of gravoturbulent formation scenario of planetesimals. In this scenario precursor material from a range of feeding zones gets concentrated in non-laminar gas structures of the solar nebula (zonal flows, vortices, and streaming instability) to gravitational unstable densities, e.g., exceeding the local Roche density. In the new funding period we will study the final collapse and possible fragmentation of these material concentrations to connect our models of precursor material evolution to the physical and chemical properties of primitive chondrites, asteroids, and cometesimals. Based on our simulations of gas and dust material evolution inside the solar nebula, we derive a time-dependent local abundance and size distribution of precursor material. We know from our magnetohydrodynamical simulations of zonal flows, vortices, and the streaming instability how strong this precursor material gets concentrated and what size segregation will occur in the overdensities. We use these overdense clouds and simulate their gravitational collapse in local high resolution hydro and dust simulations basically down to the solid density (which is only 2-3 orders of magnitude in spatial resolution), i.e., we can spatially resolve the forming planetesimals by up to 1000 grid cells in volume. Thus, we can measure, for instance, the fraction of chondrules vs. the mass fraction in matrix material. Chondrules will in this process be the most mobile particles, driving the dynamics of the collapse, whereas the matrix material is passively dragged along by the gas, and will only at a so far unpredicted level get incorporated into the planetesimal. By varying the initial mass, volume, and size distribution within the precursor cloud we can find the sweet spot that produces a certain kind of chondritic material. We can link the properties of a chondrite to its precursor properties and its formation time and location inside the nebula. One can already speculate that during the evolution of the nebula different locations and times will produce different sized chondrites with varying internal size distributions. By testing the properties of our artificial population of planetesimals to the observed data on size distributions of the material in chondrites, its chemical variations, and size distributions of asteroid belt and Kuiper belt objects and their observed binarity, we can improve our model of precursor evolution of planetesimal building material and also test the physical conditions for planetesimal formation.

我们研究了从早期太阳星云中嵌入的球粒和基质物质的引力不稳定云的星子的形成。微行星的前体物质（球粒或球粒大小的颗粒加上基质物质）由于早期太阳星云中的凝结、碎裂和漂移而演化。在我们的项目中，我们连接的预测丰富的前体物质的组成的原始陨石的框架gravoturbulent的形成方案的星子。在这种情况下，来自一系列馈送区的前体材料集中在太阳星云的非层流气体结构中（纬向流，涡旋和流动不稳定性），达到重力不稳定密度，例如，超过了当地的罗氏密度在新的资助期内，我们将研究这些物质集中的最终崩溃和可能的碎片化，以将我们的前体物质演化模型与原始陨石，小行星和彗星的物理和化学性质联系起来。基于我们对太阳星云内部气体和尘埃物质演化的模拟，我们得到了一个随时间变化的局部丰度和前体物质的尺寸分布。我们知道从我们的磁流体动力学模拟的纬向流，涡，和流动的不稳定性有多强，这种前体材料得到集中，什么尺寸的偏析将发生在超密度。我们使用这些过密的云，并在局部高分辨率的水和尘埃模拟中模拟它们的引力坍缩，基本上达到固体密度（空间分辨率只有2-3个数量级），即，我们可以通过多达1000个体积的网格单元来空间分辨形成中的微行星。因此，我们可以测量，例如，球粒的分数与基质材料的质量分数。在这个过程中，球粒将是最移动的粒子，驱动坍缩的动力学，而基质材料则被气体被动地沿着，并且只会在迄今为止无法预测的水平上被纳入微行星。通过改变初始质量、体积和前体云中的尺寸分布，我们可以找到产生某种物质的最佳点。我们可以将球粒陨石的性质与其前身的性质及其形成时间和星云内的位置联系起来。人们已经可以推测，在星云演化的过程中，不同的位置和时间将产生不同大小的星云，内部大小分布也不同。通过测试我们的人工种群的性质，对观测数据的大小分布的材料在陨石，其化学变化，小行星带和柯伊伯带的对象和它们的观测双星的大小分布，我们可以改进我们的模型的先驱演变的星子建筑材料，并测试的物理条件的星子形成。