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IN THE NEWS: Agency decides new categories of planets; Pluto falls
The International Astronomical Union (IAU) recently resolved that planets and other bodies, except satellites, in the solar system be classified into three distinct categories: a planet, a dwarf planet or a small solar system body. This new structure redefines Pluto from a planet to a dwarf planet.
IN THE NEWS: Agency decides new categories of planets; Pluto falls
The International Astronomical Union (IAU) recently resolved that planets and other bodies, except satellites, in the solar system be classified into three distinct categories: a planet, a dwarf planet or a small solar system body. This new structure redefines Pluto from a planet to a dwarf planet.

EXPERT OPINION: Dr. J. Allyn Smith, assistant professor of physics and astronomy at Austin Peay State University, said the IAU's new definition of a planet reflects the changes in technology, such as more enhanced telescopes and instruments, that are helping astronomers to discover more.

“We didn't find the things before that we're finding now,” Smith said. “The way telescopes have developed is helping us to see things that are farther away. But in this case, it all gets down to what is the definition of a planet.”

According to the IAU, a celestial body is a planet if it is in orbit around the sun, has sufficient masses for its self-gravity to overcome rigid body forces so that it assumes a nearly round shape and has cleared the path around its orbit. A dwarf planet, on the other hand, is similar to a planet, but it has not cleared the neighborhood around its orbit.

“It has to orbit a sun or a star, rather than another planet,” Smith said.

Pluto was downgraded to dwarf planet because it has not cleared its neighborhood of smaller bodies, Smith said. Under the new definition, however, three dwarf planets would be added to the Earth's solar system. For now, there are eight major planets that orbit around the sun.
“I expect this to be revisited in the near future to consider whether Pluto should become a full-fledged planet again,” Smith said.

Smith earned a Ph.D., two Master of Science degrees and a bachelor's degree all from the Florida Institute of Technology. Formerly a visiting professor of physics and astronomy at the University of Wyoming, Smith has refereed nearly 100 publications and published several abstracts. Currently, he has four research projects under way.

For further comments or information, contact Smith by telephone at (931) 221-6104 or by e-mail at smithj@apsu.edu.

Created by the APSU Office of Public Relations and Marketing, “Local Angle” is a service to selected media. Telephone Melony Leazer, communication specialist, at (931) 221-7868. The opinions expressed are those of APSU faculty and do not represent the official opinion of Austin Peay State University.