On this day in 2006, the International Astronomical Union made one of the most controversial decisions in modern science: stripping Pluto of its planetary status and reclassifying it as a "dwarf planet." After 76 years as the ninth planet in our solar system, Pluto was effectively demoted, leaving astronomers, space enthusiasts, and heartbroken schoolchildren worldwide divided.
The story begins in 1930, when astronomer Clyde Tombaugh discovered Pluto at the Lowell Observatory in Arizona. For decades, it proudly completed the planetary lineup on classroom posters and science textbooks everywhere. However, the discovery of other similarly sized objects in the Kuiper Belt - including Eris, which is actually slightly more massive than Pluto - forced scientists to reconsider exactly what qualifies as a planet.
The IAU established three criteria a celestial body must meet to earn full planetary status. Pluto failed the third requirement: clearing the neighborhood around its orbit. And just like that, the solar system officially had eight planets.
Celebrated informally around the world, the occasion invites stargazers and science lovers to revisit the debate, dust off telescopes, and perhaps feel a twinge of nostalgia for the little world that lost its title. NASA's New Horizons mission in 2015 revealed Pluto to be surprisingly complex, featuring mountains, plains, and a heart-shaped nitrogen glacier. Demoted or not, Pluto clearly still has personality. Some astronomers continue arguing for its reinstatement - the debate, much like Pluto itself, refuses to disappear quietly.