Expert: Courtney Seligman - 6/28/2009

Question
            hello

  It's well known that the Moon is going away from the Earth at few centimers per years; but will it keep on doing so in order to eventually escape from Earth's attraction? If it will, then in how many years?


                      thank you  

Answer
The Moon's retreat is caused by the tidal interaction of the Earth and Moon. This interaction transfers rotational energy from the body of the Earth to the orbit of the Moon, slowing our rotation and enlarging the Moon's orbit. The eventual result will be to cause the Earth to always keep one face to the Moon, the same way the Moon always keeps one face to the Earth. At that time, if memory serves correctly, the Moon will orbit the Earth, and the Earth will rotate on its axis, once every forty (current-length) days. That would correspond to an Earth-Moon distance about 30% larger than now, or about 325,000 miles.

So no, the Moon will not move away indefinitely. In fact, it may not even get to the distance stated above, as it would take tens of billions of years for this to happen, and the death of the Sun, about seven billion years hence, may put an end to the Earth-Moon system.