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Each day, as the sun sets, the moon rises. And as the sun rises to peer over city skylines, country fields, mountain peaks and ocean views, the moon sets. In this predictable pattern, the moon always returns. It is our planet’s loyal and constant companion. But do you know why Earth has a moon? Nature.com helps us explain.
This icon of the night’s sky plays an important role in our everyday life. Not only does the moon control daily tides, but because it is large enough to stabilize our planet's rotation, it also is responsible for Earth’s climate.
Understanding how something so critical to the human race came to be is an important mystery planetary scientists are trying to solve.
Currently, the leading theory for why the moon exists is that a Mars-sized planet collided with Earth in its infancy. This giant crash caused Earth to begin rotating at an extremely fast rate and eject debris into orbit. The orbiting material eventually melded together to form our moon.
This theory places enough material into orbit that we know it would be possible to form a moon, and it also explains why Earth contains at least 20 percent more iron than the moon. But unfortunately, while the math is correct in explaining our 24-hour day, planetary scientists still disagree over the size of the impactor and the effect it had on the Earth’s rotation.
So while planetary scientist can’t yet agree on one theory, we’re sure we can all agree that when the moon sets, the sun will always rise, and when the sun sets, the moon will always rise.
Looking for more Never Stop Asking "Why?" questions? Catch up on all of the past "Whys" on Pinterest or on the blog!
