You're asking about the farthest planet from the sun. There are two possible answers, depending on how you define "planet":

* Neptune: If we're talking about the traditional eight planets in our solar system, Neptune is the farthest.

* Pluto: While Pluto is now classified as a dwarf planet, it's still farther from the sun than Neptune at times due to its elliptical orbit.

So, the answer really depends on whether you're considering Pluto as a planet or not.