Evolution of decimeter bodies - The missing link in planetesimal formation

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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.