"Now scientists say Pluto isn't a planet. It isn't big enough. It's something, but not a planet exactly.
My attitude is: Who says?
It's been a planet my entire life. I learned that in the third grade. Might be the only thing I remember from the third grade.
It's the cold one, the farthest from the sun and, yes, it's the small one."
A view to which I have some degree of sympathy. I like Pluto. I even like it as a planet. But science isn't about what we like to be true, it's about what actually is true. The International Astronomical Union didn't arrive at the definition of planet capriciously, it built the definition around the physical characteristics of the phenomenae - that is, they insisted the definition of a planet mean something.
And so we now have 8 planets. Four gas giants, Neptune, Uranus, Saturn and Jupiter, and four rocky; Mars, Earth, Venus and Mercury.
Pluto is now (correctly) regarded as not being a planet because its gravity hasn't pulled it into a round shape.
Instead, it becomes the nearest of the Kuiper belt object,s a halo of fragments, that orbits our sun at a great distance and outside of the solar plane.
The fact is, this is not only a fair definition of planet, its a meaningful one. Delineating the difference between a moon (orbiting a body other than the parent star), as well as an asteroid (like Ceres), meant that we also had to let go of Pluto.
Fair enough I say. The IAU's definition of planet is reasonable, and coherent.
There are 8 planets.
Science. It rolls over our third grade educations every time.