The Sun has already exhausted its hydrogen reserves and will enter the red giant phase in around 5 billion years.
The red giant phase of the sun will have a deep impact on the Earth-Moon system and it is almost sure that the moon will disintegrate in future.
The space through which the Earth and the moon orbit will be crowded with more molecules. Our Moon is continuously moving away from the Earth at a rate of 4cm per year and during the time of the Red Giant its orbit will be 40% more than it is today.
Our Earth is also slowing down its rotation speed. This will continue till the time the moon takes 47 days to complete one revolution around Earth. At that time Earth will also be slowed and will take 47 days for a single rotation. That means that the moon and the Earth will continuously stare each other at the same point.
But under the Sun’s influence the moon will disintegrate and form a ring around Earth. This ring will not be permanent and the pieces will eventually fall back to the Earth. That means that if Earth is lucky enough and survives the attack by the sun it will get lonely and will get even more slow in completing the rotation.
Possible Natural Alternatives
There is a natural phenomenon that can prevent the moon from ever disintegrating. If the Sun looses 20% of its mass prior to reaching us then both Earth and Moon could be spared and will remain together facing each other for eternity. The outcome of the Red Giant phase remains a theoretical uncertainty because the astronomers have never observed a red giant star during this crucial phase.
Via: space
