Ask A Scientist© Astronomy Archive

Question:  Can a habitable planet or planets exist in a star system with more than one
star in it?
Theoretically speaking of course...
timothy a pecoraro

Answer 1:  Yes. But with some important restrictions. The orbits of the planets
must be far from the orbit of any of the multiple stars or the system
won't be gravitationally stable. This comes from the famous "three-
body problem" of orbital mechanics. If the system is a "close binary"
then planets could be orbiting both stars as if the stars were a single
"sun." Another possible stable configuration would be for planets orbiting
star A while star B was far enough away not to affect the planets. The
"in between" case of star B and planets all orbiting star A at the usual
planetary distances is only possible if star B is very small, not much
bigger than a large gas giant planet like Jupiter. In fact, if Jupiter
was 2 or 3 times more massive, it *would* be a small star!
Addendum: most (over half) stellar systems in our galaxy are binaries.
hawley