The role of planetesimal fragmentation on giant planet formation

In the standard scenario of planet formation, terrestrial planets and the cores of the giant planets are formed by accretion of planetesimals. As planetary embryos grow the planetesimal velocity dispersion increases due to gravitational excitations produced by embryos. The increase of planetesimal relative velocities causes the fragmentation of them due to mutual collisions. We study the role of planetesimal fragmentation on giant planet formation. We analyze how planetesimal fragmentation modifies the growth of giant planet's cores for a wide range of planetesimal sizes and disk masses. We incorporate a model of planetesimal fragmentation into our model of in situ giant planet formation. We calculate the evolution of the solid surface density (planetesimals plus fragments) due to the accretion by the planet, migration and fragmentation. The incorporation of planetesimal fragmentation significantly modifies the process of planetary formation. If most of the mass loss in planetesimal collisions is distributed in the smaller fragments, planetesimal fragmentation inhibits the growth of the embryo for initial planetesimals of radii lower than 10 km. Only for initial planetesimals of 100 km of radius, and disks greater than 0.06 Msun, embryos achieve masses greater than the mass of the Earth. However, even for such big planetesimals and massive disks, planetesimal fragmentation induces the quickly formation of massive cores only if most of the mass loss in planetesimal collisions is distributed in the bigger fragments. Planetesimal fragmentation seems to play an important role in giant planet formation. The way in which the mass loss in planetesimal collisions is distributed leads to different results, inhibiting or favoring the formation of massive cores.