The scientists agreed that for a celestial body to qualify as a planet:
- it must be in orbit around the Sun
- it must be large enough that it takes on a nearly round shape
- it has cleared its orbit of other objects
Pluto was automatically disqualified because its highly elliptical orbit overlaps with that of Neptune. It will now join a new category of dwarf planets.
Of course when they say "Sun" I take it they mean Star and by clearing its orbit of other objects they dont count moons or Earths moon would disqualify it as well.
Basically what it all boils down to is that Pluto is now too small for scientists to call it a planet and that is because there are other items in the solar system that are of a similar size, or bigger. Therefore astronomers created a measurement and stated that Pluto was now too small to be a planet, regardless of any attachment others may have to the idea. There are now 8 planets not 9.
Just be thankful that these astronomers are not politicians. "We're sorry Ireland, your land mass is too small to qualify for nation status, please hand in your passports and pick up your new French ones". Or vets, "We're sorry miss, your pet is too small to qualify as a dog, we have reclassified it a gerbil."
I do have to wonder what will happen when they go home to their wives tonight, "Hi honey, how was the conference. Oh by the way while you were away I reclassified some of your vital parts...."