Termination of planetary accretion due to gap formation

The process of gap formation by a growing planetary embryo embedded in a pl anetesimal disk is considered. It is shown that there exists a single param eter characterizing this process, which represents the competition between the gravitational influence of the embryo and planetesimal-planetesimal sca ttering. For realistic assumptions about the properties of the planetesimal disk and the planetary embryo, a gap is opened long before the embryo can accrete all the bodies within its region of influence. The implication of t his result is that the embryo slows its growth considerably and, thus, larg e bodies formed during the coagulation stage should be less massive than is usually assumed. For conditions expected at 1 AU in the solar protoplaneta ry disk, gap formation is expected to occur around bodies of mass less than or similar to 10(24) g. The effect of protoplanetary radial migration is a lso discussed.