As I'm sure most of you know, in 2006 the International Astronomical Union (IAU) demoted Pluto to the status of dwarf planet. That is unless you live in Illinois, where in 2009 the government decided to legally classify Pluto as a planet and make March 13 Pluto day. (And guess where the guy who discovered Pluto was from…. Illinois!)
To be a planet, the object must fit three criteria:
- The object must orbit the Sun (Pluto does this)
- The object must have enough gravity to pull it into a spherical shape (Pluto looks round, so that's ok)
- The object must clear out the area immediately surrounding it (yeah… not so much)
Number 3 is the kicker. Pluto is part of what we call the Kuiper Belt; a collection of tens of thousands of small objects that orbit the outermost part of our solar system. All the other planets have nothing (except maybe some moons) near them. Pluto, on the other hand, has thousands of objects, some smaller some bigger, in its near vicinity. So this put the IAU in a tough spot. They either had to demote Pluto, or name and classify thousands of other round objects in the Kuiper belt as planets. I don’t know about you, but I'd prefer not to have to memorize a thousand planet names! But I still feel bad for Pluto.
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