4 ms·

Isn't the moon already tidally locked?

• marcosdumay 6y ago
  Its rotation is locked to its translation. Its translation isn't locked to Earth's rotation (that's why we have tides). It will eventually become, but I think the Sun will burn everything up earlier.
  • DubiousPusher 6y ago
    Oh, I didn't even realize that was possible. So the moon would only ever be visible from the same half of Earth?
    • marcosdumay 6y ago
      Sure they tend to get in sync, they are interacting, aren't they? Due to conservation of momentum, tides can't just change the Moon's orbit without affecting something else. That something else is Earth's rotation. And the only way to take energy out of the system while still conserving momentum is for the Moon to move into a higher orbit while the Earth rotation slows (because the Earth rotation is faster). That can lead to either the Moon being ejected from orbit or to its rotation being locked with the Earth day (that gets very long). Our current configuration leads to the later. But none of those will actually happen. The Earth tides from the Moon rotation are just not relevant enough for them locking on a Sun-like star lifetime.