Is Pluto a planet after all? 'Dwarf' could be due an upgrade

Whether it's a planet, a dwarf – or just an astronomical hot potato – the status of Pluto provokes surprisingly strong feelings

The Planets
(Image credit: Michael Brown/Getty Images News)

Almost a decade after Pluto lost its status as a planet, a Harvard debate has fuelled hopes among some that its prestige may one day be restored.

The demotion came in 2006 when the International Astronomical Union (IAU) redefined the term "planet", excluding Pluto and assigning it the more lowly label of "dwarf planet".

Why? Well, the new official definition states that a planet is a celestial body that is in orbit around the Sun, is round or nearly round, and has "cleared the neighbourhood" around its orbit of solar system debris.

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It was judged that Pluto failed to meet the third of these criteria. However, the demotion proved controversial. Passionate views are held on either side.

A recent debate at the Harvard-Smithsonian Center for Astrophysics came down on the side of the Pluto boosters, The Independent reports.

In front of an audience of experts and members of the public, Owen Gingerich, who chaired the IAU planet definition committee, argued that "planet" is a "culturally defined word that changes over time" - and said that Pluto fits the bill. "The IAU was foolhardy to try and define the word," he said.

Dr Dimitar Sasselov, the director of the Harvard Origins of Life Initiative, agreed with Gingerich, declaring that any lump of matter large enough to form a sphere around a star should be classified as a planet.

Opposing both of them, Gareth Williams, from the IAU's Minor Planets Center, argued that since Pluto has not cleared a path through the space debris in its orbit, it must remain a dwarf.

However, Williams position was rejected by the audience, who voted in favour of restoring Pluto's planetary status.

The vote is neither official nor binding, but it displays how much support there is for the little ex-planet.

Planetary scientist Alan Stern told NBC that evolving knowledge of the solar system supports Pluto's claim. "The original view, until 10 or 15 years ago, was that we had four Earthlike terrestrial planets, four gas giants and the misfit Pluto," he wrote.

"But the new view is four terrestrial planets, four gas giants and hundreds of Plutos. It's jarring, because Pluto's no longer the misfit. It's the Earthlike planets that are the misfits."

Bill Nye, "the Science Guy", who describes himself as a "longtime fan of Pluto", comes to the opposing conclusion. In an email to the Huffington Post, he wrote: "I love Pluto as much as the next guy, but it has a different origin from the traditional planets and orbits in a different plane. It might be exciting to have names for hundreds of new (very old) planets, but I would be fine with eight 'traditionals' and hundreds of 'Plutoids'."

David Grinspoon, a curator of astrobiology at the Denver Museum of Nature and Science, believes that the entire semantic debate itself is an embarrassment to his field. "I'm getting sick of this," he wrote in Sky & Telescope. "Do planetary scientists really want to be known as the community that can't stop fighting about what a planet is, during a decade when we are actually finding more planets every year than in all of human history, and launching spacecraft to solve mysteries of planetary climate, landscapes, and habitability?"

Feelings run high, and not just in the scientific community. The final word, for now, must go to the third-grader from Pennsylvania who wrote to the Hayden Planetarium in protest at the 2008 decision. "Why do you think Pluto is no longer a planet?" demanded Emerson York. "Pluto is my faveret planet!!! PLUTO IS A PLANET!!!!!!!"

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