A small team of planetary scientists from the California Institute of Technology, Université Côte d'Azur and Southwest Research Institute reports possible new evidence of Planet 9. They have published their paper on the arXiv preprint server, and it has been accepted for publication in The Astrophysical Journal Letters.
But then why isn‘t Ceres also a Planet? Or Eris? Or Quaoar? Or any of the other objects classified as dwarf planets
The answer is easy: Besides their size, they all behave very differently from the actual Planets. Doesn’t mean they’re any less important, they’re just something slightly different.