Proto-Earth, Theia, and How the Moon Lost Its Iron Core

The formation mechanism of the Moon, specifically addressing why the lunar body possesses a disproportionately smaller iron core compared to Earth, is the central topic. The prevailing scientific hypothesis involves a colossal impact event between the early planet, often termed Proto-Earth, and a Mars-sized protoplanet named Theia. This ancient collision is theorized to have ejected significant material into orbit, which eventually accreted to form the Moon.

The resulting structure of the Moon reflects the energetics and mechanics of this impact. The majority of the Earth's original iron core remained with the larger planet, while the ejected material, primarily derived from the mantle regions of both impactors, constituted the bulk of the subsequent lunar body. This process explains the Moon's lower overall density and less metallic core relative to Earth's proportions.