Comment by p-e-w
7 hours ago
> Our view of the universe we live in changes over time as we get more information about it.
But that’s not what happened here. The definition was changed. We didn’t learn anything new about Pluto that made us say “ah, we thought Pluto had a solid core but apparently it doesn’t, so it’s not a planet”. All the relevant facts about Pluto remained the same. The reason why it’s no longer considered a planet is because of the term ‘planet’, not because of Pluto.
We didn't learn much more about Pluto, other than it wasn't as unique as we once thought. We learned a lot more about other bodies in the Kuiper belt though. By our old classification, suddenly it looked like there could be hundreds of "planets" in our solar system. Our improved understanding of the nature of the Kuiper belt and its inhabitants caused us to reassess which types of features were useful to distinguish a planet from the vast number of smaller objects in our solar system.