The definition of planet the IAU came up with in 2006 was shortsighted. It was crafted to make sure that only bodies that formed from the accretion disk are planets, hence the third definition part. (By the third part, Neptune is not a planet since it has not finished clearing Pluto out of its path.)
Their whole definition falls apart when applying it to the almost weekly announcement of new planets orbiting other stars (which also violates the first part.) Do we know if those new planets have cleared their paths? Do we know if they are all in their ecliptic planes? We don't even know if they are spherical (although I don't know how they couldn't be for the size we have been finding.)
Why should it matter how a body got into orbit around a star? If we have a huge round ball orbiting, it is a planet. Doesn't matter if it is in the ecliptic or 90 degrees off. Doesn't matter if it was born there or left on the doorstep from a close stellar encounter. Should we do the same for moons? Jupiter has four moons and umpteen dwarf moons? Mars has no moons?
I would rather say we have dozens of planets orbiting the sun than the current artificial distinction. Modify the definition above to replace sun with star in the first part and get rid of the third part completely. Then just live with the idea that there are still planets orbiting the sun waiting to be discovered.
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