"�This is about the fifth or 10th prediction like this. � Not one has panned out,� said Alan Stern, a planetary scientist at the Southwest Research Institute who is the principal investigator for NASA�s New Horizons mission to Pluto and beyond." <a href="http://www.geekwire.com/2016/planet-nine-astronomers-boost-the-case-for-seeking-a-large-planet-x/"></a>
See also:
1)
Tyche
2)
1983 - The Search For Planet X
The big question mark: The entire mass of the entire Kuiper belt is about the mass of Earth's moon.
Doesn't seem likely a giant planet would be able to form so far away, which is fine if the planet was ejected from the solar system somehow.
If they find such a planet it would be awesome (but quite unusual, according to astronomers).
They did some extensive scanning around for Tyche and came up with nothing and pretty much ruled that hypothetical planet out.
"They argued that evidence of Tyche's existence could be seen in a supposed bias in the points of origin for long-period comets."
" In 2014, NASA announced that the WISE survey had ruled out any object with Tyche's characteristics, indicating that Tyche as hypothesized by Matese, Whitman, and Whitmire does not exist."
Tyche isn't the same as this "Planet Nine". Tyche would have been Saturn or Jupiter sized (larger).