- The ‘giant impact’ hypothesis, first proposed in the 1970s, suggests that the Moon was formed from the debris scattered when a Mars-sized planet slammed into the early Earth some 4.5 billion years ago. This fits well with what we know about the Moon, including its mass and lack of any significant iron core.
- Since lunar and Earth rocks have such similar compositions, this suggests that Earth and the planet that smacked into it resembled each other too. They would have needed to be sister planets, with a relationship much closer than that of any other planetary bodies we have studied in our Solar System. The odds of this being possible were thought to be around a 1% chance.
- Now it seems that the scenario is not so far-fetched. He and his colleagues performed simulations of the Solar System’s formation, to investigate how similar planets tend to be to their last giant impactor. They estimated that for 20% to 40% of collisions, the two bodies would be sufficiently similar to explain the Moon’s composition.
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