Pluto should be classified as a planet again, say scientists

Could Pluto be a planet again? (Picture: Nasa)
Could Pluto be a planet again? (Picture: Nasa)

Pluto could be a planet after all, scientists have said.

New research from the University of Central Florida says the reason Pluto lost its planet status in 2006 was not valid.

In 2006, the International Astronomical Union established a definition of a planet that required it to “clear” its orbit, or in other words, be the largest gravitational force in its orbit.

Because Pluto’s gravity is influenced by neighbouring Neptune and it shares its orbit with frozen gases and objects in the Kuiper belt, it lost its planet status.

However, a study published last week insists Pluto should be a planet again.

Philip Metzger, a planetary scientist at the Florida Space Institute, said this classification is not supported in the previous research literature.

In his own research, published in the journal Icarus, Dr Metzger reviewed information from the past 200 years and found only one publication, from 1802, that used the clearing-orbit requirement to classify planets. He said it was based on reasoning that has since been disproved.


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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,” said Dr 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.”

He described the IAU’s definition as “sloppy”.

He added: “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.”

Dr Metzger said Pluto is “more dynamic and alive than Mars”, adding: “The only planet that has more complex geology is the Earth.”

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