  A binary star system is the most common result of the star formation process,
and binary companions can disrupt both the formation of terrestrial planets and
their long term prospects for stability. We present results from a large set of
numerical simulations of the final stages of terrestrial planet formation -
from Moon- to Mars-sized planetary embryos to planets - in main-sequence binary
star systems. We examine planetary accretion around both stars ('P-type'
circumbinary orbits) or individual stars ('S-type' orbits) in binary systems,
including terrestrial planet formation around each star in Alpha Centauri AB,
the closest binary star system to the Sun. For comparison, we also simulate
planetary growth from the same initial disk placed in the Sun-Jupiter-Saturn
system and also around the Sun with neither giant planets nor a stellar
companion perturbing the system. Our simulations show that giant and stellar
companions not only truncate the disk, but hasten the accretion process by
stirring up the planetary embryos to higher eccentricities and inclinations.
Terrestrial planets similar to those in our Solar System formed around
individual stars in simulations with the binary periastron (closest approach)
greater than about 5 AU. Terrestrial planet growth within circumbinary disks
was uninhibited around inner binary star systems with binary apastrons (maximum
separation) less than ~0.2 AU. Results from our simulations can be scaled for
different stellar and disk parameters. Approximately 50 - 60% of binary star
systems - from contact binaries to separations of nearly a parsec - satisfy
these constraints. Given that the galaxy contains more than 100 billion star
systems, a large number of systems remain habitable based on the dynamic
considerations of this research.
