Planet formation in binary star systems.

Nearly all previous theoretical studies of planet formation have examined the growth of planets around a single star. Several lines of evidence, however, suggest that planet formation may be common within binary star systems. More than half of all main-sequence stars, and nearly all pre-main sequence stars, reside in binary/multiple star systems. Further, at least 19 extrasolar planets orbit one member of a binary system, and numerous disks of gas and dust have been observed around one or both components of a binary system. Herein, the formation and long-term stability of terrestrial-mass planets in binary star systems is explored. More than 200 numerical simulations have been performed with two symplectic algorithms that have been designed to examine accretion around one or both stars of a binary system. Simulations of accretion in the alpha Centauri AB binary system show that terrestrial planets may have formed around alpha Cen A and/or alpha Cen B provided that an accretion disk began at a low inclination ( ≲ 30°) relative to the stellar orbit. Terrestrial planets may also form around close-binary stars with stellar apastron distances (the largest separation of the stars) QB ≲ 0.4 AU, which includes ∼10% of all main-sequence binary systems. Terrestrial planets similar to those in the Solar System may form around one component of a wide-binary system if the stellar periastron (the closest approach of the stars) qB ≳ 7 AU, and approximately 50% of binary systems fall within this range. Given that the galaxy contains more than 100 billion star systems, and that ∼60% remain viable for the formation and maintenance of Earth-like planets, a large number of systems remain potentially habitable based on the dynamic considerations of this dissertation.Ph.D.AstronomyPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/124296/2/3137926.pd