Effects of planetary radius contraction on scattering

Sammanfattning: The observed high orbital eccentricities of many giant exoplanets is thought to be the result of gravitational scattering between planets. Outcomes of planet-planet scattering can result in some planets being lost by ejections into interstellar space, or collisions between planets or with the star. The likelihood of collisions for a planet with a certain mass, increases with larger radii. After planets have been formed they will then cool and contract, which probably affects the rate of collisions and the evolution of planetary orbits. The purpose of this thesis is to examine how planetary contraction affects the outcomes of planet-planet scattering. By the use of numerical simulations I analyze of the outcomes of three 1 M_J planet systems with fixed 1 R_J, 1.5 R_J, 2 R_J radii, as well as a changing radii that follows a contraction curve from a cooling model for giant planets based on general cooling theory of Brown Dwarfs. The results show that larger planetary radii indeed lead to more collisions, which in turn produces lower final eccentricity distributions. While the timescales for collisions remained the same as for the fixed radii, more collisions occurred earlier within that time-frame for the changing radii systems. The use of present-day radii underestimates the rate of collisions, which planetary systems with contracting radii giants otherwise experience. The cumulative eccentricity distribution for simulations with changing radii also showed lower final eccentricities, as expected from the increased collision rate. Although the 2 R_J set showed similar amounts of collisions and ejections as the changing radii simulation, the final eccentricity distribution differed significantly. Perhaps suggesting that the time dependence of the collision rate has an effect on planetary orbital evolution.