  Recent exoplanet observations have revealed a diversity of exoplanetary
systems, which suggests the ubiquity of radial planetary migration. One
powerful known mechanism of planetary migration is planetesimal-driven
migration (PDM), which makes planets undergo significant migration through
gravitational scattering with planetesimals. Here, we present the results of
our high-resolution self-consistent $N$-body simulations of PDM, in which
gravitational interactions among planetesimals, the gas drag, and Type-I
migration are all taken into account. Our results show that even small
protoplanets can actively migrate through PDM. Moreover, a fair fraction of
them migrate outward. This outward migration can give a solution for the
''planet migration problem'' caused by Type-I migration and explain the origin
of Jovian planets.
