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Pluto might have to make room for 50 other dwarf planets

Australian researchers challenge the definition of a dwarf planet. If the International Astronomical Union changes the definition of a dwarf planet, then Pluto might receive yet another blow to its status and become one of 50 other dwarf planets.
Written by Boonsri Dickinson, Contributing Editor on

I feel sorry for Pluto. First, the International Astronomical Union (IAU) stripped away Pluto's planet status and reclassified it as a dwarf planet in 2006. And now, Australian scientists claim that being a dwarf planet isn't all that rare: 50 or more planets might also join Pluto's family. The Australian researchers put it this way: It's like being part of a VIP club, until you realize everyone has access too.

Technology Review reports:

The problem boils down to separating the potato-shaped objects in the Solar System from the spherical ones. What [Charles Lineweaver and Marc Norman at the Australian National University in Canberra ] have done is show from first principles how this dividing line falls naturally between objects that are larger and smaller than 200 kilometers in radius.

Their approach is simply to look for a potato-sphere threshold in images of bodies in the Solar System. The empirical evidence suggests that the threshold lies at about 200 km.

Currently, there are eight planets, five dwarf planets, and thousands of other small bodies in our solar system. By IAU standards, a dwarf planet not only has to orbit the Sun, but it also has to be nearly round with a diameter of 400 km or more. But the Australian National University scientists think dwarfs only need to have a potato radius. If the researcher's proposed 200 km radius holds up in front of the IAU, then objects classified as dwarf planets could increase tenfold.

ABC News in Australia reports:

Dr Charley Lineweaver of the Australian National University's Planetary Science Institute believes that definition is fairly arbitrary.

"If a body has enough mass, its own gravity forces it into a spherical shape, without enough mass it remains potato shaped," he says. "If it's large enough to be round then it should classified as a dwarf planet."

This post was originally published on Smartplanet.com

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