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E. W. Thommes, M. J. Duncan (Queen's University, Kingston, ON), H. F. Levison (SwRI, Boulder, CO)
Plantesimal accretion models of planet formation have been quite successful at reproducing the terrestrial region of the Solar System. However, in the outer Solar System these models run into problems, and it becomes very difficult to grow bodies to the current mass of the ``ice giants," Uranus and Neptune. Here we present an alternative scenario to in-situ formation of the ice giants. In addition to the Jupiter and Saturn solid cores, several more bodies of mass ~10 MEarth or more are likely to have formed in the region between 4 and 10 AU. As Jupiter's core, and perhaps Saturn's, accreted nebular gas, the other nearby bodies must have been scattered outward. Dynamical friction with the trans-Saturnian part of the planetesimal disk would have acted to decouple these ``failed cores" from their scatterer, and to circularize their orbits. Numerical simulations presented here show that systems very similar to our outer Solar System (including Uranus, Neptune, the Kuiper belt, and the scattered disk) are a natural product of this process.