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Project Progress

Mayer and Quinn have continued performing simulations of giant planet formation by fragmentation of a gaseous disk. This work is being extended on several fronts. We are studying the fragmentation scenario in binary star systems. This is clearly important since a majority of stars are in binaries. We conclude that if a binary companion is sufficiently close, planet formation in either the fragmentation model or the planetesimal model is completely suppressed. We are also investigating the quality of our simulations on several fronts. First, with Mejia, we are comparing the results of Lagrangian simulations with Eulerian simulations of the same system. Second, with Lufkin , we are incorporating radiative transfer into the simulations in the flux-limited diffusion approximation. With Mejia, we are also incorporating solids into our gas dynamical simulations.

Lufkin and Quinn have published their work on planet migration in gaseous disks, where they demonstrate that the standard picture of a smooth migration inward is probably incorrect, and that the process is rather chaotic involving close encounters and collisions of giant planets. A more complete survey of migration parameters is now underway as part of Lufkin ‘s Ph.D. thesis.

Barnes and Quinn, in collaboration with Lissauer ( Ames ), continue their simulations of planetesimal accretion in the terrestrial region. The simulations are reaching the point where the timescales for run-away growth can be seen. The aim is to determine the mass spectrum of planetesimals coming out of the middle stage of planet formation as a function of distance from the Sun.

Barnes, Quinn and Raymond continue to investigate the stability of extra-solar planetary systems as they are being discovered. They continue to find that most planetary systems, including our own, are on the edge of being unstable. If this is a general principle of planet formation, then predictions can be made about unseen planets in existing extrasolar planetary systems. We are investigating this possibility and have submitted several papers with our predictions.