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What do you mean, I'm not a planet?

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This user or group remembers Pluto.

--The Shoemaker Talk Red FactionDinosaur.gif 15:21, 21 July 2009 (BST) If this is vandalizing, then whatever. I think it isn't, seeing as I'm supporting Pluto. Either way, no harm is done. A three second delete process, or a good read for some people.

Pluto Facts Diameter- 1,485 miles Mass- 12.5 x 1021 kilograms Density- 1,750 kg/m3 Surface Gravity- 0.58 m/s2

Arguments For Pluto

The controversy surrounding the planetary designation of Pluto sounds deceptively simple. While Pluto was identified as a planet upon its discovery in 1930, recent refinements in the taxonomy of orbital bodies have raised questions about whether Pluto is "really" a planet, or one of the smaller, more numerous objects beyond Neptune that orbit our Sun. Part of the controversy is essentially semantic: there is no rigid, formal definition of "planet" that either includes or excludes Pluto. The other eight planets are a diverse group, ranging greatly in size, composition, and orbital paths. Size is the primary distinction that sets them apart from the thousands of smaller objects orbiting the Sun, such as asteroids and comets. Pluto, however, is much smaller than the other planets but much larger than the bodies found in the asteroid belts. This fact alone has prompted some scientists to "demote" Pluto as a planet.

Size is not the only issue raised by astronomers who want to reevaluate Pluto's planetary status. For example, they point out that Pluto's orbit differs significantly from that of the other planets, and that its composition is more similar to comets than to the other planets. Scientific organizations, such as the International Astronomical Union, however, maintain that Pluto is a major planet, and that such distinctions are arbitrary.

Perhaps the most compelling aspect of this controversy is what it says about our understanding of the solar system. The image of our solar system consisting of one Sun and nine planets is elegant, easy to picture, and has been a staple of astronomy textbooks for more than 70 years. But as scientists learn more about the smaller bodies that orbit our Sun, and look far beyond Pluto and see a wide population of other orbital bodies, it seems simplistic and naive to view Pluto as the outer boundary of the solar system. If Pluto is re-assigned to the broader category of "Trans-Neptunian Objects," one of the small, solar system bodies orbiting beyond Neptune, it would become a recognizable exemplar of a group of far-off objects made mysterious by their distance from us, but nevertheless a part of our solar system.

Pluto, the last major planet of Earth's solar system, has been considered a planet since its discovery in 1930 by American astronomer Clyde W. Tombaugh at Lowell Observatory in Flagstaff, Arizona. Tombaugh was conducting a systematic search for the trans-Neptunian planet that had been predicted by the erroneous calculations of Percival Lowell and William H. Pickering. Some scientists maintain that the only reason Pluto is considered a planet today is because of the long, ongoing and well publicized search for what was then referred to as Planet X. When Pluto was discovered, media publicity fueled by the Lowell Observatory "virtually guaranteed the classification of Pluto as a major planet," according to Michael E. Bakick in The Cambridge Planetary Handbook.

However, it is not the public opinion that determines whether a celestial body is a planet or not. That responsibility rests with a scientific body known as the International Astronomical Union (IAU), the world's preeminent society of astronomers. In January of 1999 the IAU issued a press release entitled "The Status of Pluto: A Clarification." In that document the IAU stated, "No proposal to change the status of Pluto as the ninth planet in the solar system has been made by any Division, Commission or Working Group." The IAU stated that one of its working groups had been considering a possible numbering system for a number of smaller objects discovered in the outer solar system "with orbits and possibly other properties similar to those of Pluto." Part of the debate involved assigning Pluto an identification number as part of a "technical catalogue or list of such Trans-Neptunian Objects." However, the press release went on to say that "The Small Bodies Names Committee has, however, decided against assigning any Minor Planet number to Pluto."

Notwithstanding that decision, in year 2000 the Rose Center for Earth and Science at New York City's American Museum of Natural History put up an exhibit of the solar system leaving out Pluto. That action received press coverage and re-ignited the controversy. Alan Stern, director of the Southwest Research Institute's space studies department in Boulder, Colorado, criticized the museum's unilateral decision, stating, "They are a minority viewpoint. The astronomical community has settled this issue. There is no issue."

Still, the argument continues, occasionally appearing in journal articles and in the popular press. However, for every argument against Pluto's designation as a major planet, there seems to be rational counter arguments for retaining that designation. Scientists who argue against Pluto being a major planet stress Pluto's differences from the other eight planets—the four inner planets, Mercury, Venus, Earth, and Mars, and the four giant planets, Jupiter, Saturn, Uranus, and Neptune. Supporters of Pluto as a major planet believe such arguments are fallacious because the two groups of planets could, as the Lowell Observatory put it in 1999, "scarcely be more different themselves." For instance, Jupiter, Saturn, Uranus, and Neptune have rings. Mercury, Venus, Earth, Mars, and Pluto do not. Mercury has an axial tilt of zero degrees and has no atmosphere. Its nearest neighbor, Venus, has a carbon dioxide atmosphere and an axial tilt of 177 degrees. Pluto has an axial tilt between those two extremes—120 degrees. (Earth's tilt is 23 degrees.)

A main argument against Pluto being a major planet is its size. Pluto is one-half the size of Mercury, the next smallest planet in our solar system. In fact, Pluto is even smaller than the seven moons in our planetary system.

"So what?" is the response of Pluto's defenders. They point out that size is an arbitrary criterion for determining the status of orbiting bodies. Mercury, for instance, is less than one-half the size of Mars, and Mars is only about one-half the size of Earth or Venus. Earth and Venus are only about one-seventh the size of Jupiter. From the standpoint of giant Jupiter, should the midget worlds of Mercury, Venus, Mars, and Earth be considered planets?

The most commonly accepted definition of a planet, according to University of Arizona educator John A. Stansberry, is that a planet is "a spherical, natural object which orbits a star and does not generate heat by nuclear fusion." For an object in space to maintain a spherical shape it has to be large enough to be pulled into that shape by its own gravity. According to that definition, "Pluto is clearly a planet," concludes Stansberry.

Detractors have also pointed out that Pluto's highly eccentric orbit has more in common with comets that originate from the Kuiper Belt than with the other eight planets in our solar system. That's true, reply Pluto's supporters, but just because Pluto has an eccentric orbit doesn't mean that it isn't a planet. Besides, Pluto's elongated orbit is only slightly more "eccentric" than Mercury's.

Another argument against Pluto being a planet is that it has an icy composition similar to the comets and other orbital bodies in the Kuiper Belt. Supporters of Pluto's planetary status argue that planets are already categorized into two unlike groups: The inner planets—Mercury, Venus, Earth, and Mars—which are composed of metals and rock, and the outer planets—Jupiter, Saturn, Uranus, and Neptune—which are, essentially, giant gaseous planets. Why couldn't there be three kinds of planets: terrestrial, giant gas planets, and icy rocks? Pluto may simply be the first planet in a new category.

Apparently Pluto is the largest of the 1,000-plus icy objects that have been discovered in the Kuiper Belt region of space. Since Pluto is the largest, that provides further support for Pluto retaining its "major planet" designation. There has to be a dividing line between "major" and "minor" planets, or as some call them, planetesimals. As Descartes reminds us, "No one of the sciences is ever other than the outcome of human discernment." In this context the quote reminds us that the distinctions we make between objects in orbit around the Sun are determined by our human decision. Planetary scientist Larry A. Lebofsky proposes that the IAU simply define Pluto's diameter of 1,413 miles (2,273 km) (almost half that of Mercury, the next smallest planet) as the smallest acceptable size for a major planet. It's an elegant solution to an argument that is fueled by differences in definitions. Let Pluto be the dividing line. In an age when we look forward to the development of technology that will soon allow us to spot orbiting bodies around other stars, it is a solution that would enable us to adopt a planetary classification scheme that would, as Stansberry puts it, provide "consistent and rational answers whether applied to our solar system, or to any other star system." --The Shoemaker Talk Red FactionDinosaur.gif 15:21, 21 July 2009 (BST)

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