In January 2015, Caltech (California Institute of Technology) astronomers Konstantin Batygin and Michael E. Brown published an article titled Evidence For A Distant Giant Planet In The Solar System, and announced calculation-based evidence of a massive ninth planet. Despite they have had started their research to demonstrate that there’s no ninth planet, they reached the exact opposite result: there must be a ninth planet beyond Pluto, and it’s probably 10 times the mass of Earth (for comparison, Neptune has 17 times as much mass compared to the Earth).
In an effort to state Planet Nine’s exact location, a team of French scientists used the data from the Cassini–Huygens (an unmanned spacecraft orbiting Saturn, launched on October 15, 1997). They couldn’t able to find the exact location of the giant planet, but they narrowed down the “possible areas”.
In an article titled “Constraints on the location of a possible 9th planet derived from the Cassini data“, scientists published their result. In the image below, the green zone is the most probable zone for the new member of our Solar System.
Planet Nine does not have an official name, and it won’t until its existence is confirmed, typically through optical imaging. Once confirmed, the IAU will certify a name, with priority typically given to a name proposed by its discoverers. It will likely be a name chosen from Roman or Greek mythology.
In their original paper, Brown and Batygin simply referred to the object as “perturber“, and only in later press releases did they use the nickname “Planet Nine“.
Brown and Batygin have also used the names “Jehoshaphat” (this expression frequently used by Isaac Asimov’s science-fiction character Elijah Baley, so I really wonder if the suggested name is coming from Asimov’s novels – the Robot and the Foundation series) and “George” for Planet Nine. Brown has stated: “We actually call it [‘Phattie’][A] when we’re just talking to each other.”