The search for Planet X was a historical endeavor to explain deviations in Neptune's orbit that ultimately failed because the original observations of Neptune were based on flawed data.

“Planet X died in 1993 a paper published by mil SSH Jr that's the same name of one of the names that came over on the Mayflower Planet X no dynamical evidence from the optical observation here's what he noticed that the orbit for Neptune was obtained from many different observatories”