Title:

  A World with Two Suns




Nader Haghighipour
Institute for Astronomy/
  NASA Astrobiology Institute




Abstract:

Current models of planet formation explain how planets are formed
around single stars. However, binary stars are the most common outcome
of the star formation process. There is considerable evidence for
protoplanetary disks in young multiple star systems, and observations
show that initial conditions for planet formation exist in binary
systems, as well. A survey of all currently known extrasolar planets
indicates that close to 25% of their hosting stars are members of binary
systems. Almost all of these binaries are wide with separations ranging
from 250 to 1000 AU. At these separations, the effect of the binary
companion on the formation and dynamical evolution of planets around the
other star is negligible. However, in close binary systems, such as
Gamma Cephei (separation of 21 AU) where a Jupiter-like planet revolves
the primary at a distance of 2.13 AU, the gravitational perturbation of
the companion can have considerable effects on the structure of the
circumstellar disk, formation of planetesimals and protoplanets,
and ultimately on the formation of habitable planets. In this paper, I
will discuss effects of the companion on the formation of Earth-like
planets in binary systems, and will present the results of a large
survey of the parameter space of the system in search of regions where
Earth-like planets can have long-term stable orbits.