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Why did the fission theory of lunar formation lose support?
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Moon
(Left) Near side of Earth's Moon, photographed by the Galileo spacecraft on its way to Jupiter. (Right) Far side of the Moon with some of the near side visible (upper right), photographed by the Apollo 16 spacecraft.
The fission theory, which proposed that the Moon formed from material flung off a rapidly spinning proto-Earth, lost support because it failed to withstand rigorous scientific scrutiny.12
Specifically, the theory faced the following challenges:
- Mechanical Implausibility: Scientists were unable to identify a combination of physical properties for a spinning proto-Earth that would successfully eject the necessary amount of material to form the Moon.12
- Lack of Evidence: There is no evidence to suggest that Earth ever rotated at the extreme speeds required to throw off such large chunks of its own mass.1
- Dynamic Constraints: Detailed analysis of the Earth-Moon system revealed that the required conditions for such an event were not supported by the laws of celestial mechanics.2
While the theory was initially considered persuasive due to the geological similarities between Earthās mantle and the Moon, these flaws led researchers to abandon it in favor of other models, such as the giant-impact hypothesis.12