In Brief

Will Pluto become a planet again?

Scientists argue that the official definition of a planet is ‘sloppy’ and that Pluto should never have been downgraded

Astronomers are calling for Pluto’s status to be re-evaluated, after the solar system’s most distant world was downgraded to a “dwarf planet” in 2006.

A new study headed by the University of Central Florida’s planetary scientist Philip Metzger suggests that “well over 100” worlds have been incorrectly classified as planets since 1802.

Metzger argues that the official definition of a planet is “sloppy” and that scientists use the term liberally because it’s “functionally useful”.

The definition was put in place by the International Astronomical Union (IAU), a group of experts responsible for handling “astronomical nomenclature” around 12 years ago, says Space.com

Under the IAU’s definition, planets must have a dominant gravitational pull in their orbit around the Sun. This is known as “orbit clearing”. 

The Moon isn’t a planet because it revolves around Earth, for instance, but Earth is classified as a planet because it orbits the Sun, which means it’s the dominant gravitational body.

Pluto was declassified to a dwarf planet when the IAU issued its official definition in 2006 because the icy world shares its orbit with objects in the Kuiper Belt, an area in the far reaches of the solar system. 

But Metzger claims there would be no planets in the solar system if the IAU’s definition was taken literally, because “no planet clears its orbit”.

Responding to the study, an IAU spokesperson told Fox News that the union hadn’t received an official proposal to alter Pluto’s classification. 

“There is a very clear, and known, way to table motions in the IAU, which is to propose an IAU Resolution through the relevant working group(s) and division,” the spokesperson said. “So far, no such resolutions have been proposed.”

The spokesperson added that it was “good and healthy” to debate these topics.

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