After Pluto's demotion as a planet, we have currently eight planets in our solar system. But Sun's gravitational pull can be felt well beyond Pluto, so is it possible to have a ninth planet beyond Pluto? I asked this question because we have Kuiper belt beyond Pluto, so there might be some Kuiper belt object which may qualified to be a ninth planet, isn't it possible?
There could well be, since when we had nine planets we were looking for planet X (planet number 10). However, the modern day designation of a planet is: "is massive enough for its own gravity to make it roughly spherical (slight "oblate-ness"), and has "cleared its neighbourhood" of smaller objects around its orbit". Hence, we would more than likely discard anything far out such as Pluto because it would belong to either the Kuiper belt or the Oort cloud. Anything further out than Neptune would likely be considered a Dwarf planet or proto-planet.