We once considered Pluto the ninth planet in our Solar System, but that changed in 2006.

Discovered in 1930 by astronomer Clyde Tombaugh at the Lowell Observatory in Arizona, Pluto was long accepted as a full-fledged planet.

However, as technology advanced, we started uncovering more icy bodies beyond Neptune, raising questions about whether Pluto should still be classified as a planet.

The Kuiper Belt and Pluto's Identity Crisis

The debate about Pluto's status intensified after 1992, when astronomers detected the first Kuiper Belt Object (KBO). The Kuiper Belt is a vast region beyond Neptune, filled with icy bodies similar to Pluto. The discovery of objects like Quaoar in 2002, Sedna in 2003, and especially Eris in 2005—which appeared to be larger than Pluto—forced scientists to rethink their definition of a planet.

The Decision to Change Pluto's Status

With more objects like Pluto being found, astronomers needed a clear definition of what makes a planet. In 2006, the International Astronomical Union (IAU) held a meeting in Prague to settle the matter.

After much debate, they voted on a new definition, stating that a planet must:

1. Orbit the Sun.

2. Be large enough for gravity to shape it into a sphere.

3. Clear its orbit of other debris.

Pluto met the first two conditions but failed the third. Because it shares its orbital path with other Kuiper Belt Objects, Pluto was officially reclassified as a dwarf planet. This decision meant that our Solar System now had only eight official planets.

The Ongoing Debate

Although the IAU made its decision, many scientists disagreed. Some argued that even Earth and Jupiter share their orbits with other objects, so the definition might not be fair. Alan Stern, the lead scientist of NASA's New Horizons mission, called the reclassification an awful decision and continues to advocate for Pluto's reinstatement as a planet.

The vote itself also sparked controversy. Only about 10% of the 2,700 astronomers who attended the Prague meeting were present for the final decision. Since then, the debate has continued in books, public discussions, and even TV shows.

Will Pluto Ever Become a Planet Again?

As our knowledge of the universe grows, definitions may change again. For now, Pluto remains a fascinating world—dwarf planet or not—worthy of exploration. The 2015 flyby of Pluto by NASA's New Horizons mission revealed stunning details about its surface, proving that Pluto still holds many secrets.

Who knows? One day, we might revisit the question of whether Pluto should be considered a planet again!

That's Why Pluto Is Not a Planet Anymore

Video by BRIGHT SIDE