This is a response I sent to the one-sided article "Searching for Planet 9" published April 19, 2022, in Big Think by writer Tom Hartsfield along with a request that I or another writer be given the chance to write a response presenting the other side of this ongoing debate.
At the Lunar and Planetary Sciences Conference in 2017, planetary scientist Kirby Runyon introduced the geophysical planet definition, which rejects the notion that an object has to clear its orbit to be a planet. Unlike the IAU definition, the geophysical definition focuses on objects' intrinsic properties rather than their location and deems any object that is not a star but is large enough and massive enough to be rounded by its own gravity a planet.
Because so many planetary scientists prefer the geophysical definition, they object to the term "Planet 9" for the hypothetical but as yet undiscovered planet in the outer solar system. Advocates of the geophysical definition count dwarf planets as full planets, so they view the solar system as already having a minimum of 13 planets and counting. In the August 5, 2018, edition of Planetary Exploration Newsletter, a publication of the Planetary Science Institute, a group of planetary scientists objected to the insensitive, one-sided use of the term "Planet 9," noting the IAU planet definition is "far from universally accepted."
This sentence contains multiple problems. There is no "we" that kicked Pluto out of the club. The sentence assumes a level of consent that never existed, especially among planetary scientists. It does not even acknowledge the fact that most planetary scientists reject the IAU definition and have done so for over 15 years.
Furthermore, Pluto is far from a "Kuiper Belt speck" or even an object between a planet and a speck. Such a statement totally ignores the New Horizons findings, which found Pluto to have planetary processes such as geology and weather, likely geological layering, floating glaciers, a layered atmosphere, interaction between its surface and atmosphere, varied terrains, windswept dunes, cryovolcanism, and a likely subsurface ocean. No Kuiper Belt "speck" has these features; such specks, like asteroids, are simply loosely held together by their chemical bonds.