I think Alan Stern is behind the persistent use of the term "planet". He's kind of been in a perpetual hissy fit about it since the IAU ruling, even though the ruling is very much in line with a paper he co-authored on the definition of planets a few years ago.

Just my opinion. He made some really unhinged comments after the ruling and insisted that he would defy the ruling and continue to use the term 'planet' in regards to Pluto.

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"Barbarism is the natural state of mankind. Civilization is unnatural. It is a whim of circumstance. And barbarism must always ultimately triumph" -- Conan