The reason why there was debate over whether Pluto constitutes a planet or not is due to the fact that in previous times, there wasn't a good definition to what a "planet" was. Scientists just found 9 of these objects that were large enough to see through telescopes that orbit our sun. And frequently the smaller things that we couldn't see we would call "asteroids" or something like that (much like the asteroid belt in our solar system). However, with the advent of better telescopes, we noticed that there were lots of things that were bigger than Pluto that orbited our sun as well. So instead of adding lots of new planets, scientists finally decided to define what "planet" was. The definition that scientists settled on is any object that has sufficient gravity to make it round-ish, orbits the sun, and has cleared its specific orbit of smaller objects (which Pluto has not done).

Pluto is not considered a planet anymore because The International Astronomical Union (IAU) voted on their first official definition of a planet, and this definition does not fit for Pluto. Scientists recognized that Pluto was really one of many dwarf planets from the Kuiper Belt.In terms of its or composition and its orbit, Pluto is unlike the other planets. There is still some controversy and disagreement amongst astronomers about the new definition of a "planet". We will have to wait and see whether the new definition "sticks" or not. For now, there are three official classes of objects in our Solar System: planets, dwarf planets, and small solar system bodies. Planets include the eight traditional planets from Mercury to Neptune, but no longer Pluto. Pluto is joined amongst the dwarf planets.

If you want to know more about Pluto, please go to the next link:

I will admit I was a little surprised when Pluto was reclassified--my bike was named Pluto! But I think it's the right thing. It's better to describe things the way they are than the way we thought they were.

That's the fundamental thing about science:
Scientists have to be willing to admit when they were wrong, so that our understanding of the universe can improve.

Here's what Bill Nye the Science Guy has to say

Here's a poem my friend wrote about the reclassification:

Number Nine

My favorite sphere they did remove
From line after the water god.
The IAU did not approve
The only orb named for a dog.