Influence of Protoplanetary Disks and Orbital Resonances on the Formation of Super Earths via Giant Impacts

Our current picture of the latest stages of terrestrial planet formation includes a final phase of giant impacts, during which proto-planets can undergo their final mass-doubling growth. Given the large population of super-Earths with large envelopes, the giant impacts phase for those systems must have taken place while the gaseous disk was still present. Nevertheless, it is generally believed that the disk tends to stabilize the planetary systems, preventing the collisions. In this work, we run N-body simulations including the eccentricity damping effects from a gaseous disk and study, for the first time, its influence on the dynamical evolution and stability of the system. Initially, we analyze the effect that eccentricity damping has over the relation between planetary spacing and a system’s instability time. We find that systems experience an increase in their instability times at smaller critical spacings as we decrease the eccentricity damping timescale. Then, we study the effect of eccentricity damping over the instability time distribution for a fixed spacing in a co-planar system with three super-Earth mass planets (~ 5 Earth Masses) orbiting a Sun-like star. We find that the disk can act as a double-edged sword: in some cases it stabilizes the system by damping the eccentricities, while in others it may reduce a system’s lifetime by forcing a divergent passage through nearby mean motion resonances, exciting the eccentricities and leading the system to instability. Finally, we study the divergent crossing of mean motion resonances and its impact on the system’s eccentricities for a simpler model of only two planets, in order to further understand the mechanism that leads some systems to become unstable at long timescales.