Planetesimals of km-size are supposed to be formed by mutual collisions of smaller bodies in protoplanetary disks. In this growth phase only the surface forces between dust particles provide internal strength of the pre-planetesimal bodies.Collision experiments in the low velocity range up to m/s with (sub)-mm size dust aggregates impacting a larger body show a transition from sticking to rebound and fragmentation. Recent experiments showed that these results cannot be scaled to tens of m/s impacts. Between 13 m/s and 25 m/s a dm-size compact dust body (micron-size SiO2) accretes 50% of the mass of a 1 cm dust projectile. Obviously, after the transition from sticking to rebound and fragmentation another transition from fragmentation to partial accretion occurs for larger velocities. The fragmentation of the projectile dissipates a large fraction of the kinetic energy and part of the projectile is able to stick. Experiments so far had an upper limit of 25 m/s for technical reasons. Thus, we constructed a setup which allows the acceleration of cm-size projectiles up to 100 m/s. Currently, collision experiments are performed with 1 cm dust projectiles impacting a 10 cm dust target at velocities between 25 m/s and 50 m/s. Recent experiments suggest that there is another transition from accretion to mass loss at higher velocities. We will present and discuss recent developments and first results at the conference. The threshold velocity for growth of dusty bodies might be close to the maximum velocities expected in protoplanetary disks. This work is part of the Research-Group No 759 funded by the DFG.
AAS/Division for Planetary Sciences Meeting Abstracts #39
- Pub Date:
- October 2007