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，从尘埃颗粒中生长出来的。根据不同的模型，尘埃团块的凝聚直接导致公里大小的物体或微行星的形式，通过重力凝聚的固体在原行星盘。在这两种情况下，分米大小的物体对原行星盘中固体粒子的演化起着至关重要的作用。它们是米级物体的直接前驱体，因此了解分米级粉尘团聚体的碰撞动力学和性质至关重要。部分和/或全部碎裂的阈值条件是凝聚模型的关键参数，因为颗粒尺寸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这样的假设，即原行星盘中的所有固体物质都已经被分米大小的物体捕获。因此，了解分米物体以约10 m/s的撞击速度碰撞的动力学对于引力驱动的微行星生长至关重要。尽管它们的重要性，没有数据之间的碰撞在这个尺寸范围内的尘埃团聚体，无论是理论还是实验，存在至今。在拟议的工作中，将进行分米级粉尘团块的碰撞实验。碎裂的临界速度将在低速实验中确定。此外，还将研究高速（> 10米/秒）碰撞动力学和碎片分布。研究结果将为凝结模型和描述引力驱动生长的模型增加关键的输入。

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.