Pluto Why Is Pluto No Longer Term Paper

Pages: 5 (1636 words)  ·  Style: MLA  ·  Bibliography Sources: 4  ·  Level: College Sophomore  ·  Topic: Astronomy


Why is Pluto no longer a Planet?

Once upon a time, not so long ago, schoolchildren all over the world learned that the planet farthest away from the sun in our solar system was Pluto. They learned mnemonic devices to remember the names of all nine planets, made models and mobiles, all with Pluto orbiting at the very end of their dioramas. But no more. In August 2006, after many years of intense debate, astronomers declared that Pluto was officially not a planet in "a wholesale redefinition of planethood that is being billed as a victory of scientific reasoning over historic and cultural influences," although the decision to create a fixed definition of what constitutes a planet is "already being hotly debated" within the scientific community (Britt, "Scientists decide Pluto's no longer a planet," 24 Aug 2006).

When the planetarium at New York City's American Museum of Natural History removed Pluto from the ranks of the planets, one astrophysicist said, looking at the changed model: "This tiny thing [Pluto] in this oddball orbit -- a planet? Give me a break...I think that, when the dust settles, people will recognize that there really are just eight planets" (Inman, 2006) Thus, with a sweep of the pen, suddenly, there were only officially eight planets in the solar system, and the models in museums across the country had one less spherical orb. The vote of the International Astronomical Union came after eight days of contentious debate that involved four separate proposals at IAU's meeting in Prague, and was voted upon by 424 scientists out of about 10,000 professional astronomers around the globe. When asked about the cultural place of Pluto, one astronomer replied: "For astronomers, this doesn't matter one bit. We'll go out and do exactly what we did," no matter what the public says, arguing that "for teaching this is a very interesting moment. I think you can describe science much better now by explaining why Pluto was once thought to be a planet and why it isn't now" (Britt, "Scientists decide Pluto's no longer a planet," 24 Aug 2006). To say that Pluto is suddenly not a planet though, of course, is somewhat incorrect, as Pluto has remained unchanged, rather it is the scientific definition and astronomer's perceptions (and voting patterns within the organization) that have shifted.

Surprisingly, until 2006, astronomy textbooks never had a single, universally agreed-upon definition for the word planet, as the IAU had never established exactly what constitutes a planet, and set specific scientific standards. However, defining a planet, or any astronomical body is always extremely difficult, as the definition must be universally applicable, to all solar systems, not just our own. In reaching a definition, one of the earlier proposed definitions during the 2006 conference read: "A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet." (Britt, "Controversial New Definition," 16 Aug 2006)

In this early proposal, gravity was the determining factor, in separating planets from moons and other astral bodies. Under this terminology, Pluto would remain a planet and its moon Charon would be reclassified as a planet, although both would carry the additional sub-classification of plutons to distinguish them from the other planets. Also, the asteroid Ceres, "which is round, would be classified as a dwarf planet, and "a far-out Pluto-sized object known as 2003 UB313 would also be called a pluton" (Britt, "Controversial New Definition, 16 Aug 2006).

But even the discoverer of 2003 UB 313 said such a definition was too broad, as it made no sense to consider the relatively petite Ceres and Charon planets and not call the larger earth's moon a planet. Also, under the definition, "a pair of round objects that orbit around a point in space that is outside both objects -- meaning the center of gravity (or barycenter) is between the two planets in space as with Pluto and Charon -- would be called double planets," and even triple planets would be possible, theoretically under the formulation, which could be problematic in classifying heavenly bodies in other solar systems (Britt, "Controversial New Definition, 16 Aug 2006). Finally, if they were round, asteroids could be classified as planets. All this would make the definition of planet simply to commonplace, or too confusing, or both, and thus render the new definition less than helpful. All taxonomies are supposed to be a guide, and if definitions are too broad, they have the opposite effect.

Instead, through a much more conservative motion made Pluto and its moon Charon, demoted in the astronomical hierarchy "because they are part of a sea of other objects that occupy the same region of space. Earth and the other eight large planets have, on the other hand, cleared broad swaths of space of any other large objects" (Britt, "Scientists decide Pluto's no longer a planet" 24 Aug 2006).Under the finally agreed upon definition, the only planets in the solar system were the eight planets of Mercury Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Dwarf planets included Pluto and any other round object that "has not cleared the neighborhood around its orbit, and is not a satellite" (Britt, "Scientists decide Pluto's no longer a planet" 24 Aug 2006). Small solar system bodies like asteroids and all other objects orbiting the sun will be classified as satellites.

Although the original proposal was criticized for diluting the meaning of the word 'planet,' the debate highlights how what constitutes a planet is hardly a solid, unchanging matter. The word 'planet' means wanderers in the sky, in contrast to the more fixed position of the stars, but this early observation of the ancients no longer holds scientific muster, as this depends upon how we see planets from earth, not how planets actually function in the universe. However, Pluto, which was discovered in 1930, was always assumed to be a planet, firstly because it was thought to be larger than it is. But its real size, combined with "an eccentric orbit that crosses the path of Neptune and also takes it well above and below the main plane of the solar system" made it more and more controversial in terms of its status within the astronomical community (Britt, "Scientists decide Pluto's no longer a planet." 24 Aug 2006).

Thus, it is not that Pluto is no longer a planet -- or that it never was, but that the definition has changed and grown more exclusive, one might say. And still the matter is far from settled amongst astronomers, as the debate rages on. The definition requires that a planet "has cleared the neighborhood around its orbit" (Britt, "Scientists decide Pluto's no longer a planet." 24 Aug 2006). But Earth, Mars, Jupiter and Neptune all have asteroids as neighbors and thus, technically one could say that their neighborhoods are not clear and thus they fail to meet the standards of classical, full planets. One planetary scientist said the definition is ambiguous, and, only half jokingly added that the IAU has not answered the question "how round is round," for a planet to be a planet (Inman, 2006). "This will be an issue in the future" he said, because "dozens of objects are going to be straddling this line. The new definition is not going to help us with this," by adding geometric definition into the picture (Inman, 2006). He tenaciously added: "I'll still continue to maintain that Pluto is a planet," he said.

Another controversial and unclear aspect of the final definition is: "What exactly is meant by a planet 'clearing its neighborhood?" And also, "although the new definition is meant to… [END OF PREVIEW]

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Pluto Why Is Pluto No Longer.  (2007, March 12).  Retrieved December 9, 2018, from

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"Pluto Why Is Pluto No Longer."  12 March 2007.  Web.  9 December 2018. <>.

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