Only 76 years after its discovery, on August 24, 2006, during the General Assembly of the International Astronomical Union (IAU), the ninth planet was officially removed from the list of known planets.
What’s even stranger is that astronomers, not planetary scientists, were the ones to vote to have it removed. The International Astronomical Union (IAU) redefined what a planet is without considering any geophysical qualities, with Pluto failing not due to its small size (it’s no bigger than the continental U.S.), but because it hasn’t “cleared the neighbourhood around its orbit.” This is a contentious topic of discussion; the previous administrator of NASA said that asteroids approach every “planet” in the solar system.
The International Astronomical Union also coined a brand-new phrase: “Pluto-class object.” Astronomers and cosmologists have never used this phrase.
The demotion of Plutoo obviously affected the IAU’s credibility.
The term “world” has replaced “planet” when referring to objects in the solar system. Instead of “dwarf planets” and “moons,” we hear phrases like “icy worlds,” “ocean worlds,” and “volcanic worlds.”
Most people don’t recall that in 2006, we had to rethink what a planet actually is. The true cause was the freshly discovered object 2003 UB313, which was initially designated Xena and eventually renamed Eris.
Eris is just slightly smaller than Pluto, but it is normally three times farther from the Sun due to its eccentric orbit around the Sun. In 2006, it was believed that Eris was bigger than Pluto, and some even predicted that it would be granted planet status at the next Congress of the International Astronomical Union.
However, the IAU began to have doubts when, in the early 21st century, numerous other candidate objects were discovered that were almost the same size as Pluto and were given new names such Makemake, Haumea, and Sedna. Eris and all these additional objects would also be planets if Pluto was one.