Proposed definition of planet should be rejected

and Pluto should be demoted

A new definition of what constitutes a planet could change the way scientists and the public talk about the solar system: it would definitively classify Pluto, questioned in recent years, as a planet and change the classification of three other objects—possibly more in the future—from asteroid to planet. The International Astronomical Union, meeting in Prague, Czech Republic, plans to vote Thursday on whether to accept or reject the proposed definition.

The definition should be rejected and Pluto reclassified as a "minor body," not a planet, according to Angela Speck, assistant professor of astronomy in Physics and Astronomy.

"Pluto should not be a planet, and neither should the other 'minor bodies' that would be classified as planets based on this definition," said Speck. "The reason we categorize space objects is to facilitate our understanding, and categorizing these bodies as planets will not help us understand them or the solar system better. They are characteristically more like asteroids, comets and each other than they are like planets."

Speck said the proposed definition, which classifies a planet as any body that orbits a star and has a mass significant enough to form it into a round shape, would cause more confusion than clarity because it could raise the number of planets in the solar system from nine to "dozens and dozens." She called on scientists to reject the new definition and pushed for Pluto to be "demoted" from a planet to a minor body. Using as examples two objects at first called planets but now classified as asteroids—Ceres and Vesta—she said that scientists should be willing to reclassify objects if they learn new information that shows they are different than originally believed.

Speck is an infrared astronomer with broad experience including stellar evolution, galactic chemical evolution, meteorites, astromineralogy and dust around evolved stars, and the optical properties of materials.

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Angela Speck
The Mizzou Stardust Group
Department of Physics and Astronomy