The Moon has apparently had some major visitors, like this one: http://www.bbc.com/news/science-environment-27688511
I read the article. That is my interpretation of it. It is, of course, one of the theories about how the current Earth-Moon system came about. A similar theory says a large body impacted the Earth, ripping part of the ocean floor from it, to form the Moon. I don't really know if Theia was a planet or an asteroid. But, it does seem to explain a few things.
You mean it's the same theory. Not getting where you think something "visited the moon"? Thea didn't visit the moon. It helped create it when it impacted Earth.
When I said "visited," I was being facetious. One theory is that Theia (or whatever body) may only have struck a glancing blow on the Earth or Moon, but the evidence seems to discount this possibility. The fission theory here suggests the Moon may have come from what is now the Pacific Ocean. http://en.wikipedia.org/wiki/Origin_of_the_Moon
If you had said the Earth was "visited", that would have been facetious. Saying the moon was visited was just incorrect. And?