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H. Levison, L. Dones, C. Agnor, R. Canup (SwRI), M. Duncan (Queen's U)
The dynamical structure of the giant planets can play an important role in determining the sizes, numbers, and general habitability of the terrestrial planets. Here we present a progress report of a continuing study of the coupling between outer planetary system architecture and inner planetary system formation. We have studied the growth of terrestrial planets in 6 different outer planetary systems: i) no giant planets, ii) the Solar System's outer planets, iii) a system with giant planets more massive than the Solar System, iv) a system with 7 Uranus-mass planets, v) a system with three Saturn-mass objects on orbits with eccentricities between 0.1 and 0.25, and vi) a system with one Jupiter with an eccentricity of 0.8. The last four systems are taken from our synthetic giant planet systems in Levison et al.~(1998; AJ, 116, 1998).
We find that the structure of the resulting terrestrial planet system is usually the result of how effectively the terrestrial planet embryos are dynamically excited. The more excited the embryos become, the fewer terrestrial planets form, the more massive these planets are, and the closer they are to the central star. In highly-perturbed systems, we typically find that one ~2 M\oplus terrestrial planet forms, which is probably too close to the star to be habitable. (Note that we did not include fragmentation in these simulations, which could be important in these extreme cases.) However, in many of the systems we studied, including our own giant planet system, the principal cause of excitation at 1AU was the self-gravity of the embryos rather than outer planet excitation. In these cases, the giant planets do not seem to play an important role in the formation of terrestrial planets in the habitable zone.
This research is supported by NASA's Exobiology Program.