Historical Study Might Help Pluto Regain Its Status as a Planet


Back in 2006, Pluto lost its status as a planet, when the International Astronomical Union concluded that it wasn’t worthy enough for the title, downgrading it to the status of a “dwarf planet.” Scientists said that the small rocky planet, which is 7.5 billion km from ours, wasn’t clearing its orbit; thus it wasn’t a planet.

When a celestial body cannot clear its orbit, it means that it is not the largest gravitational force in its orbit. Considering Pluto spends its time in the Kuiper belt and shares its orbit with many other space rocks, scientists agreed that Pluto must get out of the planet’s club.

But new research at the University of Central Florida, which was published in the journal Icarus, argues that it was a hasty decision.

A “Sloppy” Definition

The lead planetary scientist, Philip Metzger, looked back at scientific literature written hundreds of years ago and found a publication from 1802 that used the same standard which classified planets. Big moons like Titan and Europa were also frequently mentioned as planets, he said:

“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. And it would leave out the second-most complex, interesting planet in our solar system.”

Metzger added that more than 100 planetary scientists used the word planet, even if it doesn’t match the IAU definition, but he explains that they use that word “because it’s functionally useful.”

Twelve years ago, Metzger said that the IAU definition is “sloppy,” and stands by his words:

“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 co-author of the study, Kirby Runyon (Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland) stated that the IAU’s definition wasn’t correct, since clearing orbit is not a standard that is used to set apart asteroids from planets:

“We showed that this is a false historical claim. It is therefore fallacious to apply the same reasoning to Pluto.”


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