Arlin Crotts
Astronomy Professor
Columbia University
In many places in a two-star system, planetary orbits will be unstable, but not all places. If the planet orbits at a large distance compared to the distance between the stars, it will remain in orbit for a very long time and will be essentially stable. Also, if the planet orbits with the same period of revolution as the stars around each other, it may be possible to find closer stable orbits. (If stars' orbits are circular, these planetary orbits would occur at the "Lagrangian points".) It is also possible to have planets orbiting close to one star in an essentially stable orbit if the second star is much farther away than the planet is from the first star.

Don Brownlee
Astronomer
University of Washington
Sure - if they are close a distant planet can orbit both for a while.

Prof. David Helfand
Professor of Astronomy
Columbia University
Yes, as long as the planet's orbit is sufficiently far away from both members of the binary star pair. The planet would then see a single point of attraction (the combined masses of the two stars) and orbit normally. If the star is too close, however, its orbit will be unstable, making it an unlikely place for life to develop because the conditions would be changing drastically over time.

Douglas Scott
Professor
University of British Columbia
If you mean in a "figure 8' pattern, this is very unlikely. That's not a stable situation. But if the two stars are close together, then the planet could orbit around both of them at some greater distance.

Dr. Michael M. Davis
Astronomer
SETI Institute
Wow! I think the answer is yes, at least for a while, but I'm no expert on this. One trivial way to do it is to have the two stars very close together, with a planet far away, but I think you want to know if there are stable orbits where the planet wanders back and forth between the two stars. Wish I knew the answer!

Yervant Terzian
Professor
Cornell University
Yes, but the orbit will be very irregular.

Mordecai-Mark Mac Low
Curator/Professor of Astrophysics
American Museum Natural History
Yes, if it is sufficiently distant and they are sufficiently close together.

Prof. Wayne G. Roberge
Theoretical Astrophysicist
Rensselaer Polytechnic Inst.
Yes, but the planet would have to be very far from both stars (much farther than the distance between the 2 stars). This is because closer planetary orbits are unstable. A lot of sci fi movies get this wrong!

Astronomer*
Yes - especially if the stars are close together and the planet is more distant. Actually, the planet will orbit the center of mass of the system. (Our planets orbit the center of mass of our solar system; this point is not exactly the center of the sun.)

Andrew Liddle
Astronomer
University of Sussex, UK
I believe so, but the orbit may be chaotic so the planet might not be suitable for life.

Karen Vanlandingham
Assistant Professor
Columbia University's Biosphere 2 Center
Possibly. Most computer simulations have shown that it would be difficult for a planet to find a stable orbit in a binary system, either around one of the stars or both of them. But I'm sure there's a few possibilities, however rare.

Astronomer*
Yes, at a large enough distance the gravitational field of a double star can be approximated as a single mass. At smaller distances, orbits are not stable over long periods of time.

Eilat Glikman
Graduate Student
Columbia University
Yes it can. The planet would have to be at a pretty precise distance from the center of mass of the two stars, but it can happen. This distance is mathematically determined from 3 pieces of information:

1. The masses of the 2 stars.
2. The distance between the two stars.
3. The mass of the planet (ie it has to be much much less massive than the stars.

In fact, it is possible to put a satellite in orbit around the earth-moon system,
though it would be very hard top do so. I believe the successor
to the Hubble space telescope will be in an orbit kind of like that one.

Professor*
Sure. No problem ... as long as the system is set up carefully. The most stable way to do it is to let the stars be very close together and the planet be much farther out than the separation of the stars. Then the planet orbits both stars almost as if they were one.

Orbits in which the planet sometimes passes close to one star and sometimes passes close to the other tend to be unstable. It is not impossible to make such an orbit survive for a longish time, but it is not easy. Much depends on whether there are other planets in the system. even small perturbations would tend to grow catastrophically.

Walter Harris
Astronomer
University of Wisconsin-Madison
Yes. There are special configurations that would allow this called Lagrange orbits. These
are orbital positions between two points where an object would hold position relative to both. Such a point orbits at the same rate as the two objects. This works for planets around 2 stars, but it's also a general rule that we use for satellites (the SOHO spacecraft is in a Lagrange orbit) and asteroids. There is a group of asteroids in our solar system called the Trojans that occupy two Lagrange points between the Sun and Jupiter.

Graduate Student*
Yes, but it's really tricky. The easiest way to do this is if the two stars are close together and the planet is far away. Then the planet can go in a circle around both stars as though it were orbiting only one star. Other situations may be possible, such as getting a planet to make a figure 8 around two stars, but that would be much harder.

Ed Churchwell
Professor/Astronomer
University of Wisconsin
This is possible if the two stars are very close together and the planet is very far away from the center of mass of the two stars.

Graduate Student*
Stars in a binary system are in orbit around their common center of mass. For a planet to
be stable in a binary system, the planet would (most likely) need to exist outside the common orbit of the stars. Any type of "figure-8" orbit which takes the planet around one star, then the other would not be able to last very long. However, if the planet were far away from both stars, it could revolve around the common center of mass of the two without much difficulty. In that case, the system could be long-lived.

Astronomer*
Yes. This happens quite frequently with multiple star systems. A simple example would be a pair of stars orbiting each other and then a single star (or planet), which is further out, orbiting the pair.

James Pantaleone
Professor of Physics
University of Alaska Anchorage
Possibly, but not likely. Computer models of planetary motion indicate that the motion of three bodies is chaotic. It is most likely that the plant would collide with one of the stars
after a short time (a few million years).

Martin Duncan
Professor of Physics
Queen's University, Canada
Yes, if the planet is on an orbit that keeps it sufficiently far from both (ie it goes around the center of mass of both of them). There are some orbits that do 'loop-de-loops" around first one then the other, but they tend to be unstable (ie at some point the planet is flung out from the system.

Steven Balbus
Astronomy Professor
University of Virginia
Yes. Or even another star can orbit them both.

Professor Rex A. Saffer
Physicist, Astronomer, Educator
Dept. of Astronomy & Astrophysics, Villanova University
Yes, if the two stars are very close together, and the planet is very far from both of them, the planet feels the gravity of both stars but responds to them almost as if there were just one star in the middle having the mass of both stars combined.

Bob Mathieu
Professor of Astronomy
Department of Astronomy, University of Wisconsin - Madison
Yes, we think so, although such a planetary system hasn't been found yet. (Only because
its difficult to find such a planet with present techniques, not because they are rare.)

Steven Novotny
Air Force Officer/Graduate Student
University of Florida Astronomy Department
If the stars are fairly close together compared to the planet, the planet should orbit their center of mass - i.e. a point somewhere between the two stars.

David Batuski
Astronomer
University of Maine
Yes, if the two stars are close together, and the planet is far from both.

Eric McKenzie
Graduate student
University of Florida
Yes, this is possible, as some binary stars are so close that they are practically touching, and they whip around each other faster than once a day. On the other hand, lots of multiple star systems (some have more than two stars) are extremely spread out, where the stars are much farther apart than Pluto is from the Sun. Systems like this could easily have different planetary systems around each of the stars.

Astronomy Professor*
Yes, this is certainly possible but one would have to worry about the gravitational stability of a planet in such an orbit, particularly over long time periods.

John Huchra
Astronomer/Professor
Harvard-Smithsonian
Yes. Put the two stars in orbit close to each other and the planet far away.

*Respondents opted for anonymity and we respect their wishes.