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 show that capture is fairly common. The lunar orbit’s three moments of inertia are consistent with a past very eccentric orbit, suggestive of 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
A new theory of the origin of the terrestrial planets—that Jupiter’s gravity pulled them inward from the outer solar system—solves longstanding scientific riddles and offers a rich agenda for further investigation.