Evolution of decimeter bodies - The missing link in planetesimal formation

行星是由千米大小的原行星体（即所谓的星子）的吸积形成的，这些原行星体是从尘埃颗粒中生长出来的。根据模型的不同，尘埃团块的凝聚直接导致原行星盘中固体的引力聚集形成千米大小的天体或星子。在这两种情况下，分米大小的天体对原行星盘中固体颗粒的演化起着至关重要的作用。它们是米大小的天体的直接前体，因此了解分米大小的尘埃团块的碰撞动力学和性质至关重要。部分和/或全部破碎的阈值条件是凝固模型的关键参数，因为颗粒大小分布强烈影响原行星盘的演化。目前关于引力不稳定性的增长模型是基于原行星盘内的所有固体物质已经被分米大小的物体捕获的假设。因此，了解以10米/秒左右的撞击速度在分米物体之间碰撞的动力学对于引力驱动的星子生长至关重要。尽管它们很重要，但到目前为止，无论是理论还是实验，都没有这种大小范围内尘埃团块之间碰撞的数据。在提议的工作范围内，将进行分米大小的粉尘团块碰撞实验。碎裂的阈值速度将在低速实验中确定。此外，还研究了高速（10 ~ 10 m/s）碰撞动力学和碎片分布。这些结果将为凝聚模型以及描述引力驱动增长的模型提供重要的输入。

Planets form by accretion of km-size protoplanetary bodies, so-called planetesimals, which grow from dust particles. Depending on the model, coagulation of dust agglomerates directly leads to km-sized bodies or planetesimals form by gravitational clumping of solids within protoplanetary disks. For both scenarios decimeter size bodies play a crucial role for the evolution of solid particles in protoplanetary disks. They are the direct precursors of meter-sized bodies, so it is crucial to understand the collision dynamics and the properties of decimeter size dust agglomerates. The threshold conditions for partial and/or total fragmentation are crucial parameters for coagulation models, as the particle size distributions strongly influence the evolution of protoplanetary disks. Current models on growth via gravitational instabilities are based on the assumption that all solid material within protoplanetary disks is already captured within decimeter sized bodies. The understanding of the dynamics of collisions between decimeter bodies at impact velocities of about 10 m/s is therefore crucial for gravitation driven growth of planetesimals. Despite of their importance, no data for collisions between dust agglomerates in this size range, neither theoretical nor experimental, exist so far. Within the proposed work collision experiments with decimeter sized dust agglomerates will be carried out. The threshold velocities for fragmentation will be determined in low velocity experiments. Additionally, the collision dynamics for high velocities (> 10 m/s) and the fragment distribution will be studied. The results will add crucial input for coagulation models and also for models describing gravitation driven growth.