Most of us carry a few “facts” around for years without ever stopping to inspect them. They came from school posters, old television specials, family conversations, trivia books, or that one teacher who explained something so confidently that it stayed with us for life. After a while, those little pieces of information stop feeling like things we learned and start feeling like common sense. The trouble is, common sense sometimes has a long memory and a poor filing system. Science changes, old explanations get corrected, and simple classroom versions are replaced by more accurate ones. Some of these myths are harmless. Some are funny. A few are surprisingly stubborn. What they all have in common is that the real story is more interesting than the version many of us grew up repeating.
#1: Pluto Is Not One of the Nine Major Planets
Pluto still has a loyal fan club, especially among people who grew up memorizing the old nine-planet solar system in school. Its status changed in 2006, when the International Astronomical Union redefined what qualifies as a major planet. Pluto orbits the Sun and has enough gravity to be rounded, but it does not clear its orbital neighborhood of debris, which is one of the requirements under the modern definition. That placed it in the category of a dwarf planet rather than a major planet.
