Sticking of Fine Particles in High-velocity Impact: Application to Size Distribution of Dust Grains in a Debris Disk

Impact experiments were conducted at a velocity of similar to 0.2-1.0 km s-1 using fine particles with several microns or submicrons in size. For metal (Cu) plate targets, as observed in previous impact experiments using projectiles with sizes larger than tens of micron, our experiments with the fine particles also show that projectile materials can remain in the crater. For brittle (SiO2 glass) plate targets, though previous impact experiments using projectiles with sizes larger than tens of microns have shown the spallation and ejection of projectile materials, our experiments with the fine particles show that irreversible inelastic deformation of targets occurred and that projectile materials can remain in the crater. This is explained by the absorption of impact energy determined via the competition between deformation and crack propagation. The deformation thus contributes to the energy absorption even for brittle materials at small sizes. Compiling our results and previous data, we found that sticking can occur in collisions with particles up to at least 1 cm for ductile (metal) targets and 10 mu m for brittle targets at several hundred meters per second. As an application, we evaluated the size distribution of dust grains in a debris disk where the sticking of fine particles is assumed to occur. We demonstrated that the collisional sticking modified the size distribution, resulting in the decrease of spectral energy distribution at millimeter wavelengths, consistent with the photometry data of this debris disk. This suggests that the sticking of fine particles occurs in this debris disk.