It was the discovery of "Eris" (originally nicknamed "Xena").
Pluto was regarded as the ninth planet, from it's discovery in 1930, until it's reclassification as a dwarf planet in 2006.
Observations of Pluto's orbit and size did not provide enough evidence to change its status from a planet. Astronomers cited factors such as its small size and irregular orbit as reasons for excluding it from the planetary classification.
Pluto lost it's "planet" status and now is called a dwarf planet.
because it is way to small for the other planets
Pluto was recently reclassified as a dwarf planet after being considered the 9th planet for over 80 years. This was due to the discovery of several Pluto-sized objects is similar orbits to Pluto, and the suspected existence of hundreds or thousands more.
Pluto lost its status as a planet in 2006 when the International Astronomical Union redefined the criteria for what constitutes a planet. Pluto was reclassified as a dwarf planet due to its size and location in the Kuiper Belt.
Dr. Tyson suggests that Pluto's status as America's favorite planet stems from its unique story and the emotional connection people have with it. He highlights how Pluto embodies the spirit of exploration and discovery, capturing the public's imagination when it was reclassified as a "dwarf planet." This narrative resonates with many, as it reflects a sense of nostalgia and attachment to the idea of Pluto as a former planet in our solar system.
Pluto is designated as a minor planet (134340 Pluto).
In 2006 Pluto was degraded to the status of dwarf planet(there is another dwarf planet, Eris, that is more massive than Pluto).
Pluto recently lost its status as a planet and is now a dwarf planet.
Pluto
In 2011, Pluto was classified as a "dwarf planet" by the International Astronomical Union. This decision downgraded Pluto from its previous status as the ninth planet in our solar system.