Today is Pluto Demoted Day. On August 24, 2006, at a meeting in Prague, Czech Republic, 424 members of the International Astronomical Union (IAU) voted to enact new rules governing the classification of planets.
The IAU narrowed the definition of a planet after the discovery of several worlds at the edge of our solar system. Pluto meets three of the requirements: It orbits the sun; has sufficient mass that its gravitational forces pull it into a round, or nearly round shape; and is not a satellite, or moon, of another object.
Pluto falls short due to its inability to “clear the neighborhood” by subsuming or slinging away debris in its path. After 76 years as a planet, Pluto was demoted to the newly-created status of dwarf planet. The IAU originally intended to include dwarf planets as a subcategory of planets but scrapped the plan because of the potential addition of dozens of planets to our solar system.
The move is still debated by scientists. Some say the definition is so vague that Earth could be called a dwarf planet, too. All we know for sure is that generations of kids lost their second favorite planet.*
Have a happy Pluto Demoted Day!
*#1: Uranus, of course!