The IAU's recent expulsion
of Pluto from the Planets rests on some highly dubious reasoning: Pluto is no longer a planet because it can't keep its orbit clean. Even leaving aside the considerable fudging to exclude the rubbish at the Trojan Points
for example, the criterion is biased in favour of planets with smaller orbits.
Take, for example, Mercury. Mercury has an orbital period of 88 days as opposed to Pluto's 248 years. In the time it takes for Pluto to orbit the sun once, Mercury has zipped around the sun over a thousand times. Guess which orbit is more likely to be cleaned up, all other things being equal? It gets worse. Mercury lives in a nice tidy orbital zone while Pluto lives in the Kuiper Belt that is so rough that even a gas giant would be hard-pressed to clear it up.
Hence in my opinion, Pluto remains a planet no matter what four hundred odd astronomers on a drinking binge in Prague think.