Once a leading theory of the origin of the Earth-Moon system, the Capture Theory is simple and intuitively plausible. The numerous instances of moons with retrograde orbits support it. The lunar orbit’s three moments of inertia are consistent with a past very eccentric orbit, which fit a capture1. However, the Moon would have to come from a different part of the solar system to account for its very depleted iron compared to the Earth’s iron, which means that it would approach the Earth at a high velocity that would prevent capture. Researchers have searched in vain for a braking mechanism that would slow it down so it could be captured. Still, the accumulated evidence and arguments make the Capture Theory a viable one.
But