08/26/2026
For 76 years, Pluto was the ninth planet. Then in 2006, astronomers did something that had never been done before: they sat down and officially defined what a "planet" actually is.
They landed on three rules. A planet must orbit its star, be rounded by its own gravity, and be massive enough to have cleared its orbital path of other debris.
Pluto passes the first two easily. But that third one is where it falls apart — Pluto shares its orbit with countless other icy objects in the Kuiper Belt, and it simply isn't massive enough to sweep them out of the way like Earth or Jupiter do in their own orbits.
So Pluto wasn't demoted because it changed. It was demoted because for the first time, we finally wrote down the rules of the club it had been sitting in for 76 years — and it didn't quite meet all of them.
It's now classified as a "dwarf planet," alongside similar bodies like Eris, Haumea, and Makemake.
Do you think Pluto should still count as a planet? 🪐