I went to a talk at the air and space Smithsonian museum in DC where Mike Brown talked about his hypothesis that "Planet X" is out there. Hes done some brilliant math and research and can show that a planet should be there, he just has to find it.
This was years ago and I haven't kept up with it but I know he was trying to get time on the Subaru telescope in Hawaii to try and find it.
This sounds like very similar hypothesis-es? (Hypothesii ?)
https://solarsystem.nasa.gov/planets/hypothetical-planet-x/in-depth/