When was Pluto not a planet anymore?

American astronomer Clyde Tombaugh discovered Pluto in 1930. From 1930 until 2006, Pluto sat comfortably beyond Neptune as the ninth planet in our solar system.

In 2006, however, changes were made. The truth is, nothing about Pluto changed, but the definition of a planet did. Once these changes became official, Pluto no longer fit the definition of a planet.