The barycenter is the center of mass of a system of objects moving under the influence of their mutual gravity. In a system of bodies with identical masses, the barycenter lies directly in the center of the two bodies. For the Earth-Moon system, the barycenter is lies 1,710 km below Earth's surface. This is because Earth is far more massive than the Moon and it is this common center of mass around which Earth and the Moon seem to go around.