Over a decade after Pluto lost its planet status, researchers of a new study argue that it should be reclassified as a planet. How did Pluto lose its planet status in the first place?

Pluto’s Planet Status

In August of 2006, Pluto lost its planetary status after the International Astronomical Union (IAU) established that for a planet to be classified as such, it must have the ability to clear the neighborhood around its orbit as the largest gravitational force in the area. As it happens, Pluto shares its orbit with various gasses and objects in the Kuiper belt, and is influenced by Neptune’s gravity.

Now, over a decade after Pluto was stripped of its planet status, researchers of a new study published in the journal Icarus argue that the very classification that caused Pluto’s downgrade is actually not supported by research literature.

Evidently, upon reviewing literature from the past 200 years, researchers found only one publication from 1802 that required orbit clearing for a planet to be classified as such and this was based on since-disproven reasoning.

‘Sloppy’ Definition

According to study lead Philip Metzger of the Florida Space Institute, the IAU definition is based on a concept that is not being used in research, and that even Saturn and Jupiter’s moons have been called planets since the time of Galileo. Further, he describes the definition as “sloppy,” stating that if it is taken literally, then no planet would be classified as such because no planet clears its orbit.

“We now have a list of well over 100 recent examples of planetary scientists using the word planet in a way that violates the IAU definition, but they are doing it because it’s functionally useful,” said Metzger.

Study coauthor Kirby Runyon of the Johns Hopkins University also describes the IAU definition as erroneous and a “false historical claim” because literature does not show clearing the orbit as a standard for determining planets from asteroids as was claimed by the 2006 IAU definition.

What Is A Planet?

It was in the early 1950s when Gerard Kuiper’s research paper differentiated planets from other heavenly bodies such as asteroids based on how they were formed, but even this is no longer a factor in considering the classification of planets.

Based on the IAU classification, a planet must be in orbit around a sun, has sufficient mass to have a nearly round shape, is not a satellite, and has cleared the neighborhood in its orbit. Dwarf planets have nearly all the qualifications apart from not clearing their orbits.

Researchers state that in defining planets, they would be better based on intrinsic properties rather than on changing properties such as its orbit. One recommendation was to classify planets based on if its gravity allows it to become spherical in shape and active geology is initiated in the body. For instance, Pluto has multiple atmospheres, evidence of moons and ancient lakes, organic compounds, and an underground ocean.

”It’s more dynamic and alive than Mars. The only planet that has more complex geology is the Earth,” said Metzger.

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