Scientists Renew Calls to Restore Pluto’s Planet Status: “A Mistake Was Made”

Twenty years after Pluto lost its place as the solar system’s ninth planet, the argument over its status remains active. Supporters continue to say the 2006 decision represented a major scientific mistake.

The dispute intensified after astronomers discovered Eris, a distant Kuiper Belt object roughly the size of Pluto. If Pluto qualified as a planet, advocates asked, why should Eris not receive the same status? Other similar bodies, including Haumea and Makemake, added to the problem.

The International Astronomical Union responded by defining a planet through three conditions: it must orbit the Sun, have enough mass to become approximately round, and clear the area around its orbit. Pluto failed the third condition. Many scientists now challenge that requirement. Planetary scientist Philip Metzger argues that an object’s position in space should not determine whether it is a planet.

Opponents of a broader definition say it could open the door to hundreds of planets, including some natural satellites. Mike Brown, who discovered Eris and became known as “the man who killed Pluto,” has argued that restoring Pluto would also raise questions about the Moon’s status.

The New Horizons mission added emotional force to the scientific dispute when it flew past Pluto in 2015. Its images revealed mountains, water ice, complex geology and signs of relatively recent geological activity. Supporters view those features as evidence that Pluto deserves planetary status. Pluto has also become a symbol of the outsider, especially in the United States, where the campaign to restore it remains particularly strong. NASA Administrator Jared Isaacman called this year for the decision to be reconsidered. Critics maintain that the 2006 ruling was necessary, while supporters say a vote replaced scientific criteria. The debate continues.