Is Pluto a planet?
In 2006, the International Astronomical Union (IAU) proposed a definition of a planet that left out Pluto, causing it to lose status and relegate it as a dwarf planet. Since Neptune’s gravity impacts its neighboring planet Pluto, and Pluto imparts its circle to solidified gases and protests in the Kuiper belt, that implied Pluto was out of planet status.
In a new study by the UCF planetary scientist Philip Metzger suggests that this standard for classifying planets is not supported in the research literature.
Metzger says there is no support in the research literature for requiring a planet to clear its orbit. The scientist reviewed the publications made in the last 200 years and found that only one, from 1802, used this requirement to classify a planet. In addition, this single publication was based on a reasoning that has since been refuted.
He said, “moons such as Saturn’s Titan and Jupiter’s Europa have been routinely 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 a defined on the basis of a concept that nobody uses in their research. And it would leave out the second-most complex, an 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. It’s a sloppy definition. They didn’t say what they meant by clearing their orbit. If you take that literally, then there are no planets, because no planet clears its orbit.”
“The literature review showed that the real division between planets and other celestial bodies, such as asteroids, occurred in the early 1950s when Gerard Kuiper published a paper that made the distinction based on how they were formed.”
“However, even this reason is no longer considered a factor that determines if a celestial body is a planet.”
Study co-author Kirby Runyon, with Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland said, “the IAU’s definition was erroneous since the literature review showed that clearing orbit is not a standard that is used for distinguishing asteroids from planets, as the IAU claimed when crafting the 2006 definition of planets.”
Metzger said, “We showed that this is a false historical claim. It is therefore fallacious to apply the same reasoning to Pluto. The definition of a planet should be based on its intrinsic properties, rather than ones that can change, such as the dynamics of a planet’s orbit. Dynamics are not constant, they are constantly changing. So, they are not the fundamental description of a body, they are just the occupation of a body at a current era.”
Metzger said, “And that’s not just an arbitrary definition. 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.”
“Pluto, for instance, has an underground ocean, a multilayer atmosphere, organic compounds, evidence of ancient lakes and multiple moons. It’s more dynamic and alive than Mars. The only planet that has more complex geology is the Earth.”
The study is published in the journal Icarus.