I just made the following statement regarding two masses, M and m, in orbit about each other. "Btw, IIRC [and I may not be... I will check], as the potential energy of the gravitational field of M, wrt to m, is converted to kinetic energy in m, the mass of M decreases according Einstein's mass/energy relationship. As m loses kinetic energy to potential energy the mass M increases. This accounts for the energy storage and exchange. Am I screwing this up or does memory serve correctly? It makes sense but that is usually a bad sign.