Okay... I had an idea for my "Shades of Gray" story, that I thought would be cool, and also amusing, but I'd like to know if it's scientifically possible, before I go ahead and use it. In the story, a human asks one of the Grays if their world (Orvan) has a moon. The Gray responds, by saying "Sometimes", to a puzzled human. My thought was this... That since the Gray's homeworld is in the Zeta Reticuli system, which is a binary, and orbits the second star, that perhaps orbiting the FIRST star, is a small planetoid, maybe like Phobos or Charon, that has such an elliptical orbit, that once every one hundred thousand years or so, that small planetoid gets close enough to Orvan, to be temporarily captured by its gravity, and orbits it as a moon, until the next interval, when Orvan's gravity again flings it back into its old orbit, around the FIRST star. I was wondering if this concept is at all doable?