A new study led by a University of Central Florida researcher became the latest to maintain that Pluto has to be reclassified as a planet and that the reasons behind its demotion to dwarf planet status in 2006 don’t hold much weight.
As recalled by BBC News in 2015, the debate over whether Pluto is a planet or not began to heat up in the first few years of the 21st century. A few years after New York’s Hayden Planetarium presented an exhibit with just eight planets, scientists discovered a number of Kuiper Belt Objects (KBOs) that were similar in mass to Pluto, with Eris standing out as looking larger than Pluto and briefly being referred to unofficially as our solar system’s 10th planet.
Ultimately, the International Astronomical Union decided in 2006 that Pluto should no longer be classified as a planet, as it was deemed to be incapable of “clearing” its orbit or being the largest gravitational force within that orbit. Meanwhile, American scientists Mike Brown and Neil deGrasse Tyson, who both pushed for its declassification, became respectively known as the “man who killed Pluto” and the one who “[drove] the getaway car” after Pluto was demoted.
While the IAU’s definition of a planet clearing its orbit held water in the sense that Pluto shares the same orbit with other KBOs and is influenced by its larger neighbor Neptune’s gravity, the UCF study cited by Phys.org noted that only one other study from the past 200-plus years defined planets in the same way, and that Jupiter’s moon Europa and Saturn’s moon Titan were both considered planets in previous years. Furthermore, the aforementioned piece of scientific literature was eventually debunked, as it was “based on since-disproven reasoning.”
“The IAU definition would say that the fundamental object of planetary science, the planet, is supposed to be a defined on the basis of a concept that nobody uses in their research,” wrote UCF planetary scientist Philip Metzger.
“And it would leave out the second-most complex, interesting planet in our solar system. 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.”
Metzger also opined that the IAU’s definition of a planet when it determined Pluto should be demoted from its planet status was quite “sloppy,” as the organization did not give a straight definition of orbit clearing. He added that the IAU’s criteria, if followed to the letter, would result in none of the planets in our universe qualifying as such, as none of them are truly close to clearing their orbit.
Talking about the criteria that could be used instead for planet classification, Metzger insisted that people should look at “intrinsic properties” when deciding whether a planet is real, such as whether it is large enough to become spherical by means of the body’s “active geology.” He concluded by saying that Pluto should be classified as a planet as its underground ocean and proof of ancient lakes are among the many features that make the dwarf planet “more dynamic and alive” than Mars.