Abstract
We consider the restricted circular three-body problem in which the main bodies have variable masses but the sum of their masses always remains constant. For this problem, we have obtained the possible regions of motions of the small body and the previously unknown surfaces of minimum energy that bound them using the Jacobi quasi-integral. For constant masses, these surfaces transform into the well-known surfaces of zero velocity. We consider the applications of our results to close binary star systems with conservative mass transfer.