Terrestrial Planet Formation in Binary Star Systems

More than half of all main sequence stars, and an even larger fraction of pre-main sequence stars, reside in binary/multiple star systems [1, 2]. Numerical simulations of the collapse of molecular cloud cores to form binary stars suggest that disks form within binary star systems [3]. The presence of disk material has been indirectly observed around one or both components of some young binary star systems [2]. Terrestrial planets and the cores of giant planets are thought to form by an accretion process within a disk of dust and gas [4, 5], and therefore may be common in binary star systems. A lower limit of 30 (Jupiter mass) extrasolar planets have been detected in so-called S-type orbits which encircle one member of a binary star system. Most of these extrasolar planets orbit stars whose stellar companion is quite far away, but 3 are in systems with stellar semimajor axes, aB, of only ∼ 20 AU. The effect of the stellar companion on the formation of these planets remains uncertain. Terrestrial planets have yet to be detected in P-type orbits (which encircle both components) of a main-sequence binary star system, but close binaries are not included in precise Doppler radial velocity search programs because of their complex and varying spectra. The presence of Earth-like exoplanets in main sequence single or binary star systems has yet to be determined, though projects that focus on searching for extrasolar terrestrial planets are currently in development and could begin to provide insight within the next few years. We have numerically simulated the final stages of terrestrial planet formation in both S-type and P-type orbits within main-sequence binary star systems using two symplectic integration algorithms that we developed for this purpose [6]. Runs are performed using various values for the stellar masses and orbital parameters in order to determine whether/where terrestrial planets can form. Multiple simulations are performed of each binary star system