The moon is Earth's only natural satellite, a rocky celestial body that orbits our planet at an average distance of about 384,000 kilometers. The most widely accepted scientific explanation for the moon's origin is the "giant impact," a high-energy collision between a Mars-sized proto-planet named Theia with the young "proto-Earth" about 4.5 billion years ago. As the newly formed moon cooled down from a hot magma ocean, layers with varying iron-content and mineral compositions crystallized to form the moon's structure that we know today.