February 18th, 1930 - August 24th, 2006
On the 24th of August in 2006 Pluto was demoted from "Planet" to "Dwarf Planet" because of a re-definition of what a "Planet" is by the IAU. A planet has to pretty much fullfill 3 things (I've generalized these quite a bit):
- Its gotta be large enough so that its round.
- Its gotta have a stable orbit around the sun.
- Its gotta have its region of space cleared of any debris.
Pluto failed on the 3rd criteria. There is still a lot of asteroids floating around out in that neck-of-the-woods. But hey, Pluto is out there all alone, its small, and it takes longer for it to go around the sun. So of course there is other debris! Hell, just a few billion years ago earth would have failed on that point too!
Also, I don't think its fair that just _one_ planet decided on such a matter for _all_ planets in the solar system.
But I do think that the IAU's method for determining planethood is sound. Therefore, I think that Pluto should be Grandfathered in as a planet.