The moon is our closest celestial neighbor. It controls the movement of the tides on Earth and its phases have inspired and guided humanity for millennia — but we still don’t know exactly how it got here.
There are many existing theories. In 1898, George Darwin, son of Charles, proposed that the moon was formed when a large molten mass was ejected by a young, fast-spinning Earth — also known as fission theory.
Capture theory, which was popular throughout the 1960s, proposed that the moon was actually a traveler from another galaxy that managed to become trapped by Earth's gravitational pull.
The moon's size compared to Earth's helped propel the concept — it is the largest satellite by comparison in our solar system. It is also in tidal lock, meaning we only see one side of it at all times.
But ever since the first manned mission to the moon in 1969, the analysis of moon rocks has mostly debunked these theories.
That is, until 1975, when the giant impact theory was reintroduced — and it describes the most dramatic scenario of all.
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