Here's why:

* Planets orbit stars and have cleared their orbital path of other objects. Pluto shares its orbit with other objects in the Kuiper Belt.

* Stars are massive balls of hot gas that produce their own light and heat through nuclear fusion. Pluto is a cold, rocky body that does not produce its own light.

So, while Pluto is a fascinating celestial object, it doesn't fit the definition of either a planet or a star.