Horizons Online Edition

Issue date: 9/14/06 Section: News

Media Credit: IAU/Lars Holm Members of the International Astronomical Union debate the proposed definition of what a planet should be in our solar system.

The International Astronomical Union recently agreed upon a new definition of a planet. Now objects such as Pluto and UB313 can no longer campaign for planet status. The most famous of these controversial objects is definitely Pluto, a mass that has been generally accepted by much of the world as the ninth planet in this solar system.

ERAU professor Dr. Art Draut informed Horizons that a planet is defined as spherical, and "can not [obstruct] the path of anything else."

Since Pluto crosses Neptune's orbit, Draut declares, "It's out."

Though widely accepted by traditional society as a planet, "Pluto has looked odd for a long time" according to Dr. Rachford. If we consider Pluto a planet, then we must consider many other items in space as planets. UB313, more commonly known as Xena, was questioned as a possible tenth planet in our solar system, but was also demoted to a 'dwarf planet' by the IAU's new definitions. Most of the astronomical community "isn't up in arms" over the decision to drop the sun's ninth planet according to Rachford; in fact, Pluto's demotion to dwarf planet status "doesn't bother me at all," he said. Pluto is 17 degrees out of plane with the rest of the solar system, a fact that Draut believes denies its claim as a planet.

Even given the irregularities, many respected scientists, including Dr. Nordstrom would argue that Pluto is "a perfectly good planet."

Pluto is unique to other masses in question because it has a moon named Charon. This attribute alone, Nordstrom argues, "distinguishes it from other objects in question." Many things in science stand only for the sake of maintaining tradition. For instance, the common understanding of electricity and magnetism is founded on conventional current, and has not changed even as new data showed inaccuracies in the theory. Charges assigned to protons and electrons were not changed when it was revealed that protons do not move in an electrical system.

Pluto is among the largest dwarf planets in the near solar system. Further, it is now a model Pluton, which is defined by the IAU as an object with an orbital period of more then 200 years, a large eccentricity, and is out of plane with the other planets. So no matter what title we give Pluto, Rachford believes it will remain an interesting subject "as long as it's still out there."

Science changes as mankind gathers more information. So what will happen to Pluto and the rest of the universe as scientific knowledge increases? Mankind is forced to adapt as it gains a better understanding of the universe; the world is no longer flat, it is round; the earth is no longer the center of the universe, it revolves around the sun. Pluto is simply another question to be answered. Once the Horizons mission returns images of Pluto in 2015, there will surely be further discussion and controversy surrounding our largest "dwarf planet."

For more information on the definition of a planet, see the IAU's official website at [www.iau.org].

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