The size difference betwwen Earth and Jupiter Is greater than between Earth and Pluto. By the nature of planetary formation there will be a continuous stream of sizes with smaller being more common. You can draw an arbitrary line on size, but it is just that. You can accept every solid body orbiting the sun as a planet, but we long ago decided against that. The current definition is garbage. There is less mass in a 1AU radius around Pluto's orbit than Earth's. Contrary to the misleading statements from those supporting the current definition, Neptune in 3D never comes within 1 AU of Pluto's orbit. Jupiter would not have counted as a planet until it "cleared" it's orbit. The only definition that makes rational sense is one that represents a phase change from the bodies that formed planets and their leftovers. The original proposal had that (gravitational collapse) but many European astronomers who don't actually study planets had a problem with having to count past ten when it came to planets. That a grade school attitude could drive a swap from a rational definition to a silly one represents a low point in modern scientific reasoning to me. Especially given that the new definition is woefully inadequate based on what extrasolar planets have been showing us. How does the current definition make any sense when gas giants can swap orbits? Most of the people who actually studying planets are not accepting the IAU definition and have decided the whole process was too flawed to bother revisiting since it came up with such an idiotic definition.

I have yet to have the challenge answered as to what other scientific term has been defined based on setting an arbitrary limit to the number of items.

Regards,
Mark