Most people alive now spent the vast majority of their lives thinking of Pluto as the 9th planet in our solar system, but all that changed in 2006 when the tiniest planet orbiting our sun was demoted to a “dwarf planet.” Yet, nine years later, people still talk about the issue, and there are even t-shirts and other memorabilia sporting phrases like, “When I was a kid, we had 9 planets.”

Some of this is just people reminiscing and having fun, but there’s also a certain amount of confusion surrounding the issue. Put simply, people don’t understand why the International Astronomical Union (IAU) declared Pluto a dwarf planet in 2006.

The most common misconception is that Pluto is no longer a planet simply because it is so small (which is not true). In reality, Pluto’s status as a planet was relatively secure until 2003 when astronomers discovered another celestial body orbiting beyond the then-planet.

It was named Eris, and it is bigger than Pluto.

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