"Wobble" of Planetary Core Friend of mine was asking about the Earth-Moon system, and he brought up an interesting question. As the Moon orbits the Earth, it imparts a slight wobble to the planet, much like the wobble used to infer the presence of planets aroubd distant stars. So he was wondering about the solid metal at the Earth's core, which is sarounded by the fluid mantle. Does the core wobble withtin the planet, going slightly off-center in a little circle once a month? I told him I thought that the wobble of the core caused by the Moon would be exactly the same as the wobble of the rest of the planet, and so the core remains stationary relative to the outside of the globe. Is this correct?