The moon is Earth's natural satellite, located about 380,000 kilometers from Earth and weighing about 1/80 of Earth's mass. Why does Earth have the moon as its companion? This question stems from the origin of the moon. The earliest theory of the moon's formation was the Earth-splitting hypothesis, which proposed that the moon was ejected from Earth due to its rapid rotation, eventually forming the current Earth-Moon system. Subsequently, scientists proposed the Earth-capturing theory, which suggested that the moon formed elsewhere in the solar system and later moved to Earth's vicinity, where it was "captured" by Earth and began orbiting it. Some believe that Earth and the moon formed at the same time, known as the co-formation theory. However, none of these three theories are fully convincing.
At present, the most popular and widely accepted theory among astronomers is the giant impact theory. It combines the advantages of the above three theories. According to this theory, in the early stages of the solar system, when the primitive Earth was just formed, a celestial body the size of Mars collided with Earth. The violent impact caused the Earth's axis to tilt, and the heat generated by the collision melted and evaporated the shell and mantle of the celestial body, carrying some small fragments and dust away from Earth. These fragments orbited Earth and gradually aggregated under the force of gravity, eventually forming the current moon. The metallic core of the extraterrestrial body was slowed down by the evaporated gases and quickly fell to Earth's surface, merging with Earth. The giant impact theory has been supported by evidence from chemistry and geology, and is now considered the most convincing theory of the moon's formation.
With the advancement of technology, our understanding of the moon will become increasingly comprehensive, and the details of the moon's origin will eventually be fully revealed.