Indeed, Pluto is an interesting one for a number of reasons. One is that much of the commotion came from the fact that the word planet is very much a cultural c

Indeed, Pluto is an interesting one for a number of reasons. One is that much of the commotion came from the fact that the word planet is very much a cultural concept, and a scientific body was attempting to redefine the word for everyone. No one would have cared if it was simply a scientific term - if Pluto was now classified as a spacial object type C instead of a spacial object type B. Another is that the reason why the IAU decided to change the definition appears to have been for cultural reasons as well. Astronomers discovered other Kuiper belt objects. This included Eris, which was more massive than Pluto. They'd either have to tell people "There are more than 9 planets, and we don't know how many there are," or kick Pluto out and continue the myth of the simple solar system (with one fewer planet now). So they went with the more conservative option, by creating a new definition of planet that still isn't formally defined, and by explicitly saying dwarf planets aren't planets. Eris was discovered in 2005, the new IAU definition of planet was agreed upon in 2006. It's worth noting that prior to this, the IAU didn't even define the word "planet," it was a popularly defined term. So there's an element of asserting control over something outside of their purview simply because they objected to the cultural connotations. Here's an interesting article from the time that shows some of the thought that went into this[1]. [1] https://www.nature.com/articles/news050801-2 https://www.nature.com/articles/news050801-2