* Similar Composition: Samples brought back by the Apollo missions showed that the Moon's composition was remarkably similar to Earth's mantle, particularly in terms of oxygen isotopes. This similarity suggested that the Moon originated from material that was part of the early Earth.
* Low Iron Content: The Moon's iron core is significantly smaller than Earth's, indicating that the impactor that formed the Moon was likely a Mars-sized object rich in volatiles (elements that easily evaporate), which would have been lost during the impact.
* Angular Momentum: The Earth-Moon system has a surprisingly high angular momentum (a measure of an object's tendency to rotate). The giant-impact hypothesis explained this by suggesting that the impact imparted a significant amount of angular momentum to the Earth-Moon system.
Other theories that were less supported by Apollo mission findings:
* Capture theory: This theory proposed that the Moon was formed elsewhere in the solar system and was later captured by Earth's gravity. However, the Apollo missions found that the Moon's composition was too similar to Earth's for this to be likely.
* Co-accretion theory: This theory proposed that the Moon formed at the same time as Earth from the same disk of material. However, the Moon's relatively low density and different composition compared to Earth's core made this theory less plausible.
While the giant-impact hypothesis remains the most widely accepted theory, it's important to note that there are still some unanswered questions about the Moon's formation. Further research and analysis of lunar samples will continue to refine our understanding of this important event.
