Why does Earth have one moon?
Show answer & explanation
Answer: Giant impact formed it
Gravity allows only one — Wrong. Gravity doesn't limit moon number—Mars has two, Jupiter has 95! Earth has one because of how it formed—giant impact hypothesis.
Giant impact formed it ✓ — Correct! Giant Impact Hypothesis: ~4.5 billion years ago, Mars-sized object (Theia) collided with proto-Earth. Impact ejected massive debris into orbit. This debris coalesced into the Moon. Evidence: Moon's composition matches Earth's mantle, low iron content, Earth-Moon system angular momentum. This explains Moon's unusual size relative to Earth (largest moon-to-planet ratio for rocky planets). Dramatic formation!
Earth captured it passing by — Wrong. Capture is possible (Neptune's Triton), but our Moon formed from debris after a giant impact, not capture.
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