For years it was thought that binary stars were incapable of holding planets with stable orbits. However in 1978, high speed computer studies were conducted at the U.S. naval Observatory by Robert S. Harrington. He noted that if a planet was orbiting a binary system at three and a half times the distance of the two stars from their centre of gravity, this planet would have a stable orbit. An inner system was also predicted to be possible. Harrington discovered that if a planet a ecosphere distance was orbiting one component of a binary system of equal size i.e. path stars of the same mass and if the outer star was at least three and a half times the distance from it’s stellar neighbour then that planet would have a stable orbit. The Alpha Centauri system is one example of this concept. Alpha Centauri A an B are about twenty four astronomical units apart. However their orbits around one another are of an elliptical shape. This would cause oscillating gravitational variations that would probably not allow a planet to stay in a stable orbit for billions of years (Dickinson, T The Universe and Beyond p67-69 Camden House Publishing). In addition, the heat from Alpha Centauri B might overwhelm the planet’s ability to remain habitable.
Perhaps a better example is that of 61 Cygni A and B. An inner solar system could possibly exist between these two stars which are 84 astronomical units apart. An earth-like planet orbiting one of these stars would not be affected by the other’s gravity or radiation. Russian astronomers in St. Petersburg in 1977 claim to have detected a wobble in both of the binaries. They claim that a large Jovian planet with with ten to twelve times Jupiter’s mass is orbiting the A binary and one with seven to eight times Jupiter’s mass is orbiting the B binary(Asimov p 129). Earth-Like planets could exist in such a system. This is a very important discovery because judging from the ratio of visible star it would appear that almost seventy percent of all stars are binaries.
