Formation of icy planetesimals
Zusammenfassung der Projektergebnisse
Due to technical reasons it was not possible to cover the complete velocity and particle size range as planned. Instead, with CO2-ice and mixed agglomerates the parameter range was extended to another material species, which is as crucial in the outer solar system as water ice. Surface forces dominate the result of collisions of small particles, so that the particle compositions play a crucial role. For the first time CO2-ice, water ice and a mixture of both has been analyzed with respect of pre-planetary coagulation. The major results of the project can be summarized as follows: • Threshold conditions for sticking and bouncing were determined experimentally for three different materials (pure CO2, pure water ice and mixture). • An analytical model has been developed to describe the coefficient of restitution for ice agglomerates. • An analytical model has been developed to describe the fragmentation strength for small agglomerates. • The critical pull-off force for small water ice grains has been measured and its dependency on the reduced radius. The results are in clear contradiction to previous theoretical studies (Kumm). Future work should extend the experimental data on coagulation of mixed agglomerates. Although the first experiments for mixtures of water and CO2 were successful, a more detailed analysis especially regarding the mass fraction of the components is still missing. The work on the contact forces between ice grains should also be extended, as the scaling laws have to be modified for small particles.
