[Previous] | [Session 44] | [Next]
D.S. McNeil, M.J. Duncan (Queen's University), H.F. Levison (Southwest Research Institute)
Planetary embryos embedded in a gas disk suffer a decay in semimajor axis -- type I migration -- due to the asymmetric torques produced by the interior and exterior wakes raised by the body (Goldreich and Tremaine 1980; Ward 1986). This presents a challenge for standard oligarchic approaches to forming the terrestrial planets (Kokubo and Ida 1998) as the timescale to grow the progenitor objects near 1 AU is longer than that for them to decay into the Sun. Using both semianalytic methods (based upon Thommes et al 2003) and large N-body integrations using a parallel implementation of the symplectic integrator SyMBA (Duncan, Levison, and Lee 1998) we investigate this problem by varying gas properties such as dissipation timescale in different models of the protoplanetary disk. We conclude that even for near-nominal migration efficiencies and dissipation timescales of ~1 Myr it is possible to maintain sufficient mass in the terrestrial region to form Earth and Venus if the disk mass is substantially enhanced over the minimum mass model. The resulting configurations differ in several ways from the initial conditions used in previous simulations of the final stages of terrestrial accretion (e.g. Chambers 2001), chiefly in (1) larger interembryo spacings, (2) somewhat larger embryo masses, and (3) up to ~1 Earth mass of material left in the form of planetesimals when the gas vanishes. The systems we produce are reasonably stable for ~100 Myr and therefore require an external source to stir up the embryos sufficiently to produce final systems resembling the terrestrial planets. In an example following Kominami and Ida (2004), we consider the effects on the evolution of our configurations of the formation of Jupiter and Saturn. Recent results and plans for future work are discussed.
[Previous] | [Session 44] | [Next]
Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.