Well, it’s official: Pluto is no longer classified as a sovereign planet. Lots of people who don’t get out much are arguing and foaming over the mouth right about now over an issue that really boils down to one thing: semantics.
The whole question is really a matter of opinion rather than science.
Folks who call Pluto a planet do so because
- it orbits the Sun independently,
- it has an atmosphere, albeit a tenuous one,
- it has a moon (actually, three), and of course,
- it’d be a real pain to rewrite all those textbooks.
They’re not wrong. However, there are many cogent arguments against it:
- its orbit is off the main ecliptic (ie. slanted in relation to the plane on which the others orbit)
- its orbit carries it through that of Neptune, and if anything, said orbit resembles that of an object captured by the Sun rather than something formed out of the initial nova (compare it to a cometary orbit)
- its composition and nature more closely resemble that of asteroids and Kuiper Belt objects than a planet formed independently.
Continued...