<Hmm. I just realized that this post would be better suited for the "Celestial Mechanics" forum. Would you mind moving this post, since it appears that I am unable to do so myself without posting twice?> To begin with, does anyone know of the confirmed existence of or believe in the possibility of binary planetary systems in which two say, earth sized or larger bodies of equal mass or of nearly equal mass are orbiting around each other while orbiting around a star in a stable orbit? The image I think of when picturing such a system is that of a rope with two balls attached on either end moving forward (or in circular motion) while the balls rotate around a central point, essentially "falling" over one another, independant of the system's outside movement. My fascination lies within the axis of rotation between these two bodies, particularly because of the unique gravitational state which would exist within such a region of space (between the two planets). Would gravity (within the aforementioned planetary system) cancel out locally if one where to enter the region (axis) central to the binary planets rotational motion? How might this change depending on the distance between these two planets? I suppose that if they were too close together, they would simply collide due to the overwhelming gravitational attration drawing one to the other. But with enough rotational velocity around a fixed point, could earth-sized or larger bodies still remain apart at relatively close distances like say, two-thirds that of the distance between the earth and the moon? I am not much of a physisist, so I haven't been able to do the math for myself... Oh, I should also add that the orbital motion of the binary planets in this instance would be arbitrarily close to uniform circular motion and non-elliptical. This is just to simplify the problem a little bit.