Many exoplanets in close-in orbits are observed to have relatively high eccentricities andfangu large stellar obliquities .
We explore the possibility that these result from planet-planet scattering by studying the dynamical outcomes from a large number of orbit integrations in systems with two and three gas-giant planets in close-in orbits ( 0.05 AU < a < 0.15 AU ) .
We find that at these orbital separations , unstable systems starting with low eccentricities and mutual inclinations ( e \lesssim 0.1 , i \lesssim 0.1 ) generally lead to planet-planet collisions in which the collision product is a planet on a low-eccentricity , low-inclination orbit .
This result is inconsistent with the observations .
We conclude that eccentricity and inclination excitation from planet-planet scattering must precede migration of planets into short-period orbits .
This result constrains theories of planet migration : the semi-major axis must shrink by 1-2 orders of magnitude without damping the eccentricity and inclination .