| MadSci Network: Astronomy |
Planets can evolve in a binary star system but only for certain configurations. Most configurations are unstable, meaning a planet cannot exist and will be flung out of the solar system, or sucked into one of the stars.
One of the new planets in another solar system, 16 Cyg b, is a planet orbiting a star where the star is part of a very wide binary system. The second star is 1000 AU away (1 AU = distance between the Earth and the Sun = 150 million km) from the parent star and so it has almost no gravitational effect on the planet.
The other case where a planet can evolve in a binary star system is when the binary stars are very close together and the planet is orbiting both stars at a large distance.
Recent calculations show that stable orbits can exist for the above 2 cases for the distance ratio of sun-planet/sun-2nd star to be 1/7 or 7/1. In other words either the 2nd star has to be 7 times farther away than the planet, or the planet has to be 7 times away than the 2nd binary star and orbit around both stars. Otherwise the gravitational forces are disruptive.
Binary star formation isn't yet well understood. Planets arise out of the dust and gas of the circumstellar disk, and some scientists think they have observations of separate circumstellar disks for binary stars evolving together.
Try the links in the MadSci Library for more information on Astronomy.