On August 24th, 2006, Pluto was officially demoted from being a planet, which apparently caused some people to be outraged.
Pluto didn’t meet the final rule, as Britannica writes:
So, what was the IAU’s reason for demoting Pluto when it did? Why is Pluto no longer a planet?
The main event of the 2006 General Assembly of the IAU, the proposal that would come to demote Pluto, was a defining moment for the rest of the solar system as well. Fiercely debated by the members of the union, the resolution that was passed officially defined the term planet. What was once a loose word used to describe a large object within the solar system was now specific: planets are celestial objects large enough to be made rounded by their gravitational orbit around the Sun and to have shooed away neighboring planetary objects and debris. Pluto is now classified as a dwarf planet because, while it is large enough to have become spherical, it is not big enough to exert its orbital dominance and clear the neighborhood surrounding its orbit.
Now that the controversy of Pluto has been cleared up, open thread.
I hear Trump may reclassify it as a planet and rename it “Planet Trumpo.”