Nibiru

A planet called Nibiru, which orbits the Sun every 3,600 years on an extended elliptical orbit akin to a comet, and passes between the orbits of Mars and Jupiter during its perihelion, according to author Zecharia Sitchin's assertion in The 12th Planet (1976). The Annunaki, who lived on Nibiru, traveled to Earth three hundred thousand years ago to mine gold to restore the planet's depleting atmosphere. When the miners rose up in revolt, the Annunaki turned to Homo sapiens, a mixture of the Annunaki and Homo erectus, to work as slaves in the mines.

Nancy Lieder, who claimed to be in mental contact with aliens who warned her that a planet will soon pass close to Earth, took this idea of a planet moving through the solar system to the heart. Some people called that planet Nibiru. (However, Sitchin mocked this and said that Nibiru's last encounter with the inner solar system was in 556 BCE, putting its return in the vicinity of 2900 CE.) Nibiru became the subject of a popular Internet conspiracy theory were images of other astronomical objects were used to support claims that NASA was concealing proof that Nibiru was approaching. Nibiru then was conflated with the end of the Mayan Long Count on December 21, 2012, which passed without the destruction of all things—but not before astronomers tired of pointing out that, if Nibiru actually existed, it would have been seen already and that any planet with such an orbit would have likely been ejected from the solar system.