A team led by Philip Metzger, planetary scientist at the University of Central Florida (UCF) in Orlando, maintained that the rationale mentioned behind dilution of Pluto’s status from a planet to a dwarf planet was erroneous.
In 2006, the International Astronomical Union (IAU) — a global group of astronomy experts — asserted that to be called a planet, it is required to be the largest gravitational force in its orbit. Pluto failed to meet the criteria as Neptune’s gravity influences it.
“The IAU definition would say that the fundamental object of planetary science, the planet, is supposed to be defined on the basis of a concept that nobody uses in their research,” Metzger said.
Reviewing scientific literature from the past 200 years, Metzger found only one publication, from 1802, that used the clearing-orbit requirement to classify planets, and it was based on since-disproven reasoning.
According to co-author Kirby Runyon, from Johns Hopkins University in Maryland, 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.
“We showed that this is a false historical claim,” Runyon said. “It is therefore fallacious to apply the same reasoning to Pluto.”
The definition of a planet should not be based on properties that can change, such as the dynamics of a planet’s orbit, instead, on if it is large enough that its gravity allows it to become spherical in shape, Metzger said.