No joke. Up until just a few years ago, we thought Pluto was a planet. Apparently, we can't even decide what a planet is. We also can't even find Planet X in our own solar system. We can find planet in other galaxies, but not our own solar system. This is what passes for science these days? Sheesh! /s
Pluto is just a matter of semantics.
Planet X is merely fantasy at this point.
Depends on what you mean by Planet X. There's a legit search for another large ice giant in the far reaches of the outer solar system.