Nibiru is a mythical planet that was supposed to have close enough to the Earth to cause The End Of The World As We Know It. This even has been predicted by people that have no credentials in astronomy, and who get most of their information regarding Nibiru from obscure Babylonian myths and gossip rags like the National Enquirer. Not one bit of direct observational evidence for the existence of Nibiru has been presented, and those pictures that have been given as such are mere photoshopped random images of Mars and Io.
No claimant has ever given any valid orbital elements or any consistent physical characteristics of Nibiru. With the correct orbital elements, I could point my Celestron CPC 925 Series 9.25" Schmidt-Cassegrain reflecting telescope in the right place and get my own images. From thos images, I could verify the physical characteristics.
But this belief in Nibiru is just like any other cult or religion - it's based solely upon faith in unprovable myths and intangible ideas, and can not be verified by simple observation merely because there is nothing out there to observe. Thus, belief in Nibiru is yet another shared delusion.
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The mere fact that science may not yet adequately explain an object, event, or experience does not mean the immediate explanation should automatically default to a conspiratorial, extraterrestrial, paranormal, or supernatural cause.