The decision to reinstate Pluto as a planet is not a recent topic of debate, however. There has been much argument over the classification of a planet since the ruling was made by the IAU.

The debate over Pluto’s status highlights the evolving nature of scientific classification. Definitions should reflect our growing understanding rather than arbitrary criteria.

While Planet X was estimated to be about six times more massive than Earth, Pluto’s mass is only 20% that of the Moon, itself 1% of the Earth’s mass. Pluto is much too small to gravitationally ...

Pluto, therefore, is not the gravitationally dominant object in its neighborhood — and thus, not a planet, according to the new definition.

Since Pluto is surrounded by many other KBOs, it hasn't achieved gravitational dominance in its region. As a result, it doesn't fulfill criterion 3, meaning it can no longer be classified as a planet.

Though Pluto has formally been considered a dwarf planet for almost two decades, it still has many lessons left for planetary scientists — including hints about how the solar system formed.

At this moment, Pluto is still classified as a dwarf planet. Despite ongoing debate and public support for its reinstatement, the International Astronomical Union has not changed its 2006 decision.

Pluto was the little planet that could — until it couldn’t. Discovered in 1930 at Lowell Observatory in Flagstaff, Arizona, Pluto was hailed as the ninth planet in our solar system.

Because Pluto did not fit the last of these requirements, after years of debate it was "demoted" to the status of a dwarf planet by a majority vote of the International Astronomical Union at its ...

Pluto was demoted from a planet to a dwarf planet in 2006. So why is its status still so controversial today? When you purchase through links on our site, we may earn an affiliate commission.

“For that reason alone, Pluto’s status as a full-fledged planet should be kept.” Tombaugh came to NMSU in 1955 and developed a world-class astronomy research program.

But why isn't Pluto considered a planet anymore? It starts with the definition of a planet — or lack thereof. Before 2006, there weren't strict criteria for a planet.