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proto-Moon
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proto-Moon

astronomy
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Quick Summary

The proto-Moon is a hypothetical early stage of the Moon's formation. While the exact origin is still debated, the most widely supported theory is the giant-impact hypothesis.

This theory suggests that about 4.6 billion years ago, a Mars-sized body named Theia collided with the proto-Earth. The immense impact ejected a massive cloud of debris, primarily composed of mantle material from both bodies. This debris then coalesced to form the proto-Moon.

Older theories, now largely discounted, included coaccretion (Earth and Moon forming together), fission (the Moon breaking off from a rapidly spinning Earth), and capture (Earth capturing a pre-formed Moon). These were challenged by observations, such as the Moon's lower density and similar chemical composition to Earth's mantle, which the giant-impact hypothesis better explains.12

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
3 Britannica Sources
  1. Where Did the Moon Come From?
  2. Moon - Origin and evolution
  3. How Big Was the Asteroid That Contributed to Dinosaur Extinction?

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