Large scattering events and the formation of planetary systems
  In the nucleated instability picture of gas giant formation, the final stage is the rapid accretion of a massive gas envelope by a solid core, bringing about a tenfold or more increase in mass. This tends to trigger the scattering of any nearby bodies, including other would-be giant planet cores; it has been shown in past work that the typical outcome is an outer planetary system very similar to our own. Here, we show that the gravitational scattering accompanying the formation of gas giant planets can also produce, in some cases, outer planets with semimajor axes much larger than those in the Solar System, and eccentricities which remain high for tens of millions of years. Rings, gaps and asymmetries detected in a number of circumstellar dust disks, which hint at the presence of embedded planets at stellocentric distances far beyond where planet formation is expected to occur, may be connected to such a scenario. 
Edward W. Thommes