Mars-Sized Crash Forged Earth's Unusually Large Moon
A Mars-sized world named Theia struck the young Earth, vaporizing rock and throwing debris into orbit that quickly coalesced into Earth's Moon, explaining why the Moon is so large relative to Earth. Apollo-rock chemistry shows the Moon is Earth-like, ruling out capture or co-formation theories. Simulations indicate the debris formed a Moon within hours, and tidal forces have since raised the length of day and pushed the Moon outward at about 3.8 cm/year, altering future solar eclipses over hundreds of millions of years.