Why Nibiru is impossible
An orbit like that of Niburu is inconsistent with modern astronomy. David Morrison, NASA space scientist explains that after just one previous flyby of Earth, such as they claim happened in Sumerian times, Earth itself would no longer be in its current near circular orbit and would be likely to have lost its Moon. A brown dwarf has even worse effects, being much heavier. He also points out that it would be one of the brightest naked eye objects in the night sky months before a flyby. Everyone would see it. And any planet sized object would be an easy target for an amateur astronomer, well beyond Pluto.
Here is David Morrison explaining this. He is senior NASA space scientist and astrobiologist, known for his work on asteroid impacts and he headed the Sagan Institute at SETI until 2014, he also used to answer questions from the public for NASA’s “Ask an Astrobiologist” which is how he came across the ‘Nibiru’ myth. This is for 2012 but it is the same for any of these dates.
In more detail have a listen to this podcast from the SETI institute with David Morrison on it with others:
Also it doesn’t matter what you call it, Nibiru, or Wormwood, or a “Dark star”. Any planet or star in such an orbit is impossible and absurd.
These “apocalyptic fables” as NASA calls them often claim that NASA has confirmed that ‘Nibiru’ exists, but without giving a link to any NASA page. For what NASA themselves say, see Why the world didn't end in 2012 [http://www.nasa.gov/topics/earth/features/2012.html). On Nibiru they have this update in 2017:
"Editor's update, Sept. 20, 2017: Various people are "predicting" that world will end Sept. 23 when another planet collides with Earth. The planet in question, Niburu, doesn't exist, so there will be no collision. As you can see from the Q&A below, the story of Niburu has been around for years (as has the "days of darkness" tale) and is periodically recycled into new apocalyptic fables.
See also Phil Plait’s