Where did the moon come from?

I've never really thought about where the moon came from. It has just always been there. After the discovery of water in moon samples, it threw off all the scientists. I guess that scientists have believed that the moon was formed 4.5 billion years ago. A planet the size of Mars supposedly smashed into the Earth & molten pieces were torn off which became the moon.

With the new discovery this means that either A. The Moon held onto the water when it was created or B. The water was gathered from somewhere within 100 million years as the moon solidified. Basically, the scientists are saying that they don't know a whole lot, maybe less than they used to think they knew, but how cool is that?