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answers:
Raymond say: There are many instances of "planet X".
For example, Pluto was discovered during an official search for a "missing planet". During the search, the hypothetical object was called "planet X" (x was for "unknown"). When the "thing" was found, it was thought to be a planet, and given the name Pluto.
In 2006, astronomers found a body a bit further out than Pluto (which, at the time, was still the 9th planet). It was also slightly bigger than Pluto. They were sure they had found the 10th planet, and temporarily called it "Planet X" (with X being the Roman numeral for 10); they even gave it the name Xena (begins with X).
However, this body is now known as dwarf planet Eris.
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A fake "Planet X" was invented for a hoax: the end of the world of May 2003. It was supposed to be a rogue planet (not in orbit around our Sun) that was going to pass too close to Earth and cause all kinds of problems. Roland Emmerich's movie "2012" is based on that hoax.
Not to be confused with Nibiru, which is a fictitious planet (invented for a fiction story, the same way Tatooine was invented for the Star Wars story). The English version of the book came out in 1971. In the story, Nibiru is in orbit around our Sun and comes close to Earth every 3600 or 3700 years (without hurting us). In the story, Nibiru's next passage close to Earth cannot come before the year 2085.
For the Big 2012 Hoax (the so-called Mayan end-of-the-world), the fake Planet X and the fictitious planet Nibiru were combined into an even-more-fake Planet X that was going to kill us all on December 21 2012 (or December 23 in the first version of the hoax).
After the 2012 end-of-the-world, Planet X has been hitting us every year. It will be that same faker-than-fake planet that will hit us again, killing us all over again, in October 2017, and again in 2018, and so on, until people understand that it is a hoax.
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