Supposedly discovered by the Sumerians and photographed by Russian scientists, Planet X, alternately known as Nibiru, is believed by some to be on a head-on collision with the Earth. The time of impact, according to conspiracy theorists? Dec. 21, 2012.
If you've heard of Planet X before, it might be because you're familiar with the hypothetical planet astronomers were looking for during much of the 20th century. Because scientists couldn't account for slight discrepancies in the orbits of Uranus and Neptune, some believed that an undiscovered planet existed somewhere in our solar system. It turns out, however, that astronomers had been overestimating Neptune's mass, and most experts dismiss the existence of a mysterious Planet X.
But that didn't stop Nancy Lieder, founder of the Web site ZetaTalk, from making doomsday predictions involving a Planet X collision. Her first prediction initially didn't involve 2012, though -- according to Lieder, the moment of impact was supposed to have been May 2003. When that didn't happen, the date was moved forward to match up with the Mayan calendar and Dec. 21, 2012.
Countless Web sites have spawned from Lieder's theories, only adding to the speculation. But officials at NASA deny the existence of Planet X or Nibiru, and denounce the idea of a massive planetary collision as an Internet hoax.