Not a joke. Pluto was an American discovery and it was declassified as a planet through corruption in 2006 by the International Astronomical Union. Further, the definition currently used by the IAU is unsupportable.
First, only 5% of astronomers got to vote on this definition. There was not much debate on the matter before it was determined. And subsequently, the IAU refuses to revisit the decision.
Second, the definition the IAU is using is irrational. It is as follows:
- is in orbit around the Sun,
- has sufficient mass to assume hydro static equilibrium (a nearly round shape), and
- has “cleared the neighborhood” around its orbit.
By this logic, many planets in our solar system would also not be planets. For example, Earth itself arguably has not “cleared the neighborhood” as evidenced by asteroids smacking into the moon or the planet Earth itself now and again. The definition is further vague and frankly entirely undefined. There is no criteria presented for it.
There are many astronomers that have taken issue with this classification. I would like the US government to put pressure on IAU to revisit this question, open the discussion up to debate, and demand that they have concrete and non-contradictory definitions of what is a planet.
Low priority, but this is another example of corruption in science by various unaccountable elites that are perverting science by exploiting institutional corruption.