Protostars and Planets VI, Heidelberg, July 15-20, 2013
Collision Dynamics of Decimeter Dust
Deckers, Johannes (Fakultšt Physik, Universitšt Duisburg-Essen)
Teiser, Jens (Fakultšt Physik, Universitšt Duisburg-Essen)
De Beule, Caroline (Fakultšt Physik, Universitšt Duisburg-Essen)
Wurm, Gerhard (Fakultšt Physik, Universitšt Duisburg-Essen)
Planets are formed by accretion of protoplanetary bodies. The collision dynamics of decimetre bodies are important for the formation of these planetesimals, as they play a crucial role in the different formation models. As direct precursors to metre size bodies they are of importance for coagulation models. In particular, the threshold between bouncing and fragmentation is significant here. But they are also interesting for models that describe planetesimal formation by gravitational collapse, as decimetre bodies can easily be trapped in vortices where critical particle densities can lead to gravitational instability.
Collisions of decimetre size dust agglomerates have not been studied experimentally yet, especially because these agglomerates are difficult to handle. We carried out collision experiments of equally sized dust agglomerates under microgravity conditions in the Bremen drop tower. The agglomerates are pressed using quartz powder, which consists of irregular grains mainly in the size range between 1 and 5 μm. The cylindrical agglomerates have a height and diameter of 12 cm, a mean volume filling factor of about 0.44 and a mass of little over 1.5 kg.
The collisions at velocities between 0.8 and 25.7 cm/s were observed by two high-speed cameras positioned perpendicular to one another. At low collision velocities the agglomerates bounce of each other. The coefficient of restitution decreases for an increasing collision velocity. For collisions beyond the threshold velocity of 16.2 cm/s one or both agglomerates fragment. This velocity corresponds to a specific kinetic energy of Q = 5 mJ/kg.
In addition to planetesimal formation, the collision dynamics of decimetre dust agglomerates are also relevant for planetary ring systems. The collision velocities are of the order of a few cm/s. With the dust agglomerates used here we can simulate the collision dynamics of regolith covered ice particles, which are common in these ring systems.
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