MACROSCOPIC DUST IN PROTOPLANETARY DISKS-FROM GROWTH TO DESTRUCTION

The collision dynamics of dusty bodies are crucial for planetesimal formation. Decimeter agglomerates are especially important in the different formation models. Therefore, in continuation of our experiments on mutual decimeter collisions, we investigate collisions of centimeter onto decimeter dust agglomerates in a small drop tower under vacuum conditions ( p less than or similar to 5 x 10(-1) mbar) at a mean collision velocity of 6.68 +/- 0.67 ms(-1). We use quartz dust with irregularly shaped micrometer grains. Centimeter projectiles with different diameters, masses, and heights are used, their typical volume filling factor is Phi(p,m) = 0.466 +/- 0.02. The decimeter agglomerates have a mass of about 1.5 kg, a diameter and height of 12 cm, and a mean filling factor of Phi(t,m) = 0.44 +/- 0.004. At lower collision energies, only the projectile gets destroyed and mass is transferred to the target. The accretion efficiency decreases with increasing obliquity and increasing difference in filling factor, if the projectile is more compact than the target. The accretion efficiency increases with increasing collision energy for collision energies under a certain threshold. Beyond this threshold at 298 +/- 25 mJ, catastrophic disruption of the target can be observed. This corresponds to a critical fragmentation strength Q* = 190 +/- 16 mJ kg(-1), which is a factor of four larger than expected. Analyses of the projectile fragments show a power-law size distribution with an average exponent of -3.8 +/- 0.3. The mass distributions suggest that the fraction of smallest fragments increases for higher collision energies. This is interesting for impacts of small particles on large target bodies within protoplanetary disks, as smaller fragments couple better to the surrounding gas and re-accretion by gas drag is more likely.