The debate about whether Pluto is or is not a planet is an interesting one in that it highlights many interesting aspects of what we study in TOK.
Pluto itself did not change but the definitions we use to define what comprises our solar system did change. When we only knew of 9 objects of a particular size orbiting the sun, the inclusion of Pluto as a planet was not controversial but as new objects were added to the list, scientists needed to come up with a definition that either excluded Pluto or added many more objects to our list of planets.
It’s important to remember that like most definitions and language, meaning is based on agreement and man made rules. There is no “cosmic” definition of a planet. This article discusses this concept to some degree.
“For years, astronomers, planetary scientists and other space researchers have fought about what to call the small, icy world at the edge of our solar system. Is it a planet, as scientists believed for nearly seven decades? Or must a planet be something bigger, something more dominant, as was decided by vote at the International Astronomical Union (IAU) in 2006?
“The issue can bring conversations to a screeching halt, or turn them into shouting matches. “Sometimes,” Runyon said, “it’s just easier not to bring it up.””
Here are some interesting comments from the article as well. They illustrate some of the interesting aspects of the “debate” where people can get very emotional about the issue, as illustrated by the first comment below. But the second comment raises an interesting question about whether we would care as much if we hadn’t discovered Pluto almost a hundred years ago.