Pluto Demoted From Planetary Status Five Years Ago Today
August 24, 2012

Pluto Demoted From Planetary Status Six Years Ago Today

Lawrence LeBlond for - Your Universe Online

On August 24, 2006, the solar system´s most distant family member -- tiny, isolated icy planet Pluto -- received some shocking news: it would no longer be considered a true planet. The ruling spurred a hotbed of controversy, with many experts disagreeing with Pluto´s new status as a “dwarf planet.”

Despite the controversy and oppositions from scientists and laypeople alike, the ruling went through, reducing the number of planets in the solar system from nine to eight, with Neptune now being the outermost planet.

When Pluto was discovered in 1930, it was viewed as an oddball, and that perception has remained constant for more than sixty years. Pluto is much smaller than the other planets in the solar system and zooms around the sun at a significantly distant 3.65 billion miles, that is nearly a billion miles farther than the next farthest planet, Neptune, is from the solar body.

It wasn´t until the 1990s that scientists began to realize that Pluto was not such an oddball after all. They found other objects in Pluto´s realm that were equally as bizarre, including the ring of icy bodies beyond Neptune known as the Kuiper belt.

The somewhat large bodies found in the Kuiper belt, which also follow orbital paths around the Sun, led many scientists to concur that these objects should also be classified as planets, since they are similar to Pluto.

Yet, continued studies led others to rethink Pluto´s planetary status, and in 2005, Caltech astronomer Mike Brown announced the discovery of Eris, a substantially larger object than Pluto, in the Kuiper belt. Shortly after his discovery, the International Astronomical Union (IAU) stepped in.

In 2006, the IAU came up with a new definition of what a planet is: A body that circles the sun without being some other object's satellite, is large enough to be rounded by its own gravity (but not so big that it begins to undergo nuclear fusion, like a star) and has "cleared its neighborhood" of most other orbiting bodies.

Based on this new definition, Pluto was deemed not a "true" planet and was re-branded, along with Eris, as a “dwarf planet.” The ruling was agreed upon by most mainstream scientists, who said Pluto, Eris and other large Kuiper belt bodies do not belong in the same category as the eight “original” planets, because they are just too different from the others.

But some scientists remained unconvinced with IAU´s definition, calling it flawed and unscientific.

Alan Stern of the Southwest Research Institute in Boulder, Colorado, said he thinks the IAU should be embarrassed by their ruling. He is leading NASA´s New Horizons mission, which is sending a spacecraft to study Pluto up close.

Stern said he doesn´t disagree with the term “dwarf” planet, he just thinks dwarfs should be considered “true” planets just as well as the terrestrial planets and gas giants. He feels that by keeping dwarfs out of the planetary equation, the IAU and other scientists can keep the list of planets down to a manageable size.

Richard H. Miller of the University of Chicago said in 2006, after the IAU ruling, that the issue of Pluto not being a planet is really a matter for the public, not science. “Some people may be upset, but we´ve long regarded it (Pluto) as a minor planet,” he said.

Philip Diamond, a professor at the University of Manchester and a delegate at the IAU meeting in August 2006, said the ruling is appropriate. “We are finding more planets in our solar system, and some are larger than Pluto.”

He said what has been done is a good thing. “we have actually expanded the number of planets in our solar system, but just spread them over two categories,” he said at the time.