Were planetesimals formed by dust accretion in the solar nebula?

The growth of meter-sized bodies in the solar nebula by dust accretion is examined. The meter-sized bodies have velocity about 50 m/s relative to the gas and small dust aggregates. When a small dust aggregate hits a meter-sized body, the aggregate breaks into dust monomers. These monomers accrete onto the body after several bouncing as proposed by Wurm et al., Icarus (2001), if the mean free path of the gas molecules is larger than the radius of the body. On the other hand, the monomers never hit the surface of the body again, if the body is much larger than the mean free path of the molecules. The sizes of bodies would be limited to the order of 10 times the mean free path. Kilometer-sized planetesimals were hardly formed by dust accretion in the region within 5 AU from the sun where the mean free path is less than 1 m. The planetesimals were probably formed by the gravitational instabilities in this region.