Recently in 2008, Japanese Astronomers at Kobe University lead by Dr. Mukai have plotted a planet with a diameter at least the size of earth should exist in our solar system on a highly elliptical orbit. This planet is normally referred to as Planet X, but sometimes also called Nibiru, which is referred to in ancient Sumerian tablets. They also talk of an alternate beginning to humans evolution. Below is a radio interview that explains this theory in depth. Very, very cool stuff.