Bring up the former planet Pluto in conversation and you’re guaranteed to be met with a strong opinion. In one camp are those ...

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

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.

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 ...

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.

Pluto had been considered our solar system’s ninth planet since its discovery in 1930. But in 1992, astronomers discovered Pluto’s small, icy neighbors in what has become known as the Kuiper Belt.

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.

In 2006, the IAU famously dropped Pluto from the pantheon of planets because it did not meet the union’s criteria. As stated on the union’s website, a planet in the solar system: ...

Pluto may have lost its status as a full-fledged planet in 2006, but that doesn't mean it's a joke of a world this April Fools' Day and the folks behind Pluto TV want to make that clear.

“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.

Pluto once held its place proudly as the ninth planet in our solar system,a distant, icy world on the edge of the cosmic frontier. But in 2006, everything changed. This in-depth explainer unpacks ...

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