Abstract
It is controversial whether the planetesimals are formed through continuous dust sticking due to non-gravitational forces, or they are formed by the gravitational instability of the dust layer in a protoplanetary disk. We examined the former process taking account of the gas flow around a dust aggregate. The results are as follows: (a) A small dust aggregate collides once with a large aggregate. The collision velocity is about 50m/s. (b) The small dust aggregate breaks into monomers by the collision. (c) The monomers never collide with the large dust aggregate due to the gas drag of the flow around the large aggregate. Thus, the planetesimal formation through dust sticking seems difficult to occur.
