In 1970, Michael Vasin and Alexander Shcherbakov of the Soviet Academy of Sciences published a shocking article in Sputnik magazine titled "Is the Moon the Creation of Alien Intelligence?" They argued that the Moon’s physical anomalies could only be explained if it were an artificial biosphere. They hypothesized that the Moon has a massive, hollow interior protected by a double-walled shell: an outer layer of meteoric rock and a thick, internal metallic hull engineered to withstand extreme temperatures and cosmic radiation.
While mainstream science rejected the alien part, the math behind the Soviets' paper was incredibly sound. The Moon possesses a major mass paradox: it is roughly 3.7 times less dense than Earth. If it formed naturally from the same material as Earth (the leading "Giant Impact" theory), their densities should be highly similar. The Moon's low density proves that it either lacks a heavy iron core like Earth, or it has a massive amount of empty, hollow space inside it.