Although this is the most popular theory for the formation of our moon, it is not the only one. Many believe the Moon was captured by the Earth after forming elsewhere. It could even be a Kuiper belt object as many of the other planets' moon may be. When we look up at the Moon at night it is difficult to imagine the Earth without it. But one day in the future, there may be no moon.
Moons are by no means permanent.
By making precise measurements with laser beams, astronomers have discovered that our moon is actually moving away from the Earth at the rate of about two inches per year. Millions of years ago, it was much closer than it is today. In fact, during the days when dinosaurs walked the planet, the Moon appeared several times larger in the sky than it does today. Astronomers believe that the Moon could one day break free of the earth's gravity and wander off into the cosmos. Other moons face similar fates.