How our Moon was formed is still up for heavy debate. One of the leading theories is the Giant-impact hypothesis. The theory follows that during our solar system’s early stages, a Mars sized object that astronomers call “Theia” collided with the Earth. This collision caused a large amount of rocky debris to form around the Earth. About half of the rocky material left over from this collision eventually was brought back together by gravity to become the Moon, while the rest had enough velocity to escape the Earth’s gravity and orbit the Sun as asteroids. Simulations suggest that the debris that formed the Moon combined together in less than 100 years. This would have definitely been quite the sight!
The Moon was originally much closer to the Earth when it formed. Using complex simulations, astronomers have calculated that the Moon was actually about 15 times closer. The Moon has slowly moved away from the Earth over time because its orbit is actually losing energy. The Moon transfers its orbital energy to Earth’s tides by its gravitational pull. You can almost think of the tides as acting like friction on the Moon’s orbit. On average, the Moon is moving away from the Earth at about 2 centimeters per year.
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