It looks like the argument on whether or not Pluto is a planet will never be resolved. Even the chief administrator of the National Aeronautics and Space Administration (NASA) Jim Bridenstine joined in on the debate claiming that Pluto is indeed a planet.
THE CONFUSION
Pluto was widely accepted as a planet for more than 70 years. But in 2006, the International Astronomical Union established a definition of what it is to be tagged as a planet: a planet should be able to clear its orbit or in exact terms used by the IAU, "clearing the neighborhood around its orbit." Meaning, in order for a celestial body to be a planet, it should become gravitationally dominant with no other celestial body close to its size except for some of its satellites.
Many astronomers including Bridenstine himself challenge this definition. During a speech at the International Astronautical Congress, he said: "I am here to tell you, as the NASA administrator, I believe Pluto should be a planet." He then continued to support his statement by saying that Pluto has an ocean present beneath its surface, and there are organic compounds on its surface.
However, the IAU's reason to remove Pluto from the list of the planets in the solar system is because of Neptune's gravity. According to the IAU, the ice giant heavily influences Pluto's movement and that its orbit is inhabited by frozen glass and debris from the Kuiper Belt.
But, some researchers claim that the IAU's definition is wrong. A study published by researchers from the University of Central Florida Orlando reviewed all published journals regarding planetary science for the past 200 years. It only found 1 publication dating back to 1802 that used the requirement of clearing the orbit as a prerequisite to be classified as a plant. Apparently, this definition was disproved a long time ago.
Lead author Philip Metzger of the Florida Space Institute explained: "Moons such as Saturn's Titan and Jupiter's Europa has been called planets by planetary scientists since the time of Galileo. The IAU definition would say that the fundamental object of planetary science, the planet is supposed to be defined based on a concept that nobody uses in their research, And it would leave out the second-most complex, interesting planet in our solar system." He also said that the team now has a list of at least 100 examples of planetary scientists using the word planet while disregarding the definition given by the IAU.
He also explained the literature showed that this division between planets and other celestial bodies started with Gerard Kuiper in the early 1950s when he published a paper that claimed the distinction between planets and other celestial bodies based on how they were formed.
Co-author Kirby Runyon of the John Hopkins University Applied Physics Laboratory also explained that the IAU's definition of a planet is fallacious since there are literature stating otherwise. "We showed that this is a false historical claim and therefore fallacious to apply the same reasoning to Pluto."
HOW DO WE DEFINE A PLANET?
According to Metzger, we should define a planet according to its intrinsic properties. He explains that since the dynamics of a planet's orbit is not constant, they should not be the fundamental description but just the occupation of a celestial body in the current era. He suggests classifying planets based on its size, if whether or not it is large enough that its gravity will allow it to be spherical.
"And that's not just an arbitrary definition," Metzger says. "It turns out this is an important milestone in the evolution of a planetary body, because apparently when it happens, it initiates active geology in the body."
