Astrophysical Object Phenomenon Thesis

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Astrophysical Object

Pluto's Demotion: From Fully-Fledged Planet to One of a Hundred Dwarfs

My Very Educated Mother Just Served Us Nine Pizzas" (Greene 2006). For years, every school child memorized this mnemonic device, to better recall the order of the planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. However, all of this changed in 2006. Then, the International Astronomical Union (IAU) met in Prague to more clearly define what constituted a planet. The Union decided that a planet must fulfill three criteria. Firstly, it must orbit the Sun, secondly it must be large enough to have a spherical shape, and thirdly, "it must have cleared out the other objects in its orbit" (Cain, "Why do some scientists think that Pluto is not a planet?" 2006). This decision spelled bad news for tiny, icy Pluto, the 9th planet in the solar system. While Pluto does fulfill the first criteria, it fails the last test. Pluto has only a fraction of the mass of the rest of the objects in its orbit, and does not dominate its moons.

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It may come as a surprise that the IAU only came to a coherent definition of what constitutes a planet in 2006. "In fact, the International Astronomical Union (IAU), charged with classifying heavenly objects, has never had a definition on record for planets. Never needed one. Everyone instinctively knew what a planet was," or so it seemed, until the 2006 resolution (Britt, 2000, p.1). Before 2006, finding even an unofficial textbook definition for the word "planet" was almost impossible. "Amazingly, many science and astronomy books -- just like the IAU -- don't define the word. You won't find a basic definition in the New York Public Library's Science Desk Reference, for example. And in the 1999 edition of Universe, a comprehensive tome used widely in college courses, "planet" is not even an entry in the 21-page glossary" wrote one science journalist in 2000 (Britt, 2000, p.1).

TOPIC: Thesis on Astrophysical Object Phenomenon Assignment

The recent controversy over Pluto's status as a planet reveals the fact that quite often, what seems like a scientific certainty is still quite contentious within the scientific community, when new discoveries are made through improved technology. In 1995, discoveries of large planets around other stars, plus new objects that are neither planet nor star, and free-floating objects in space that look like planets but do not orbit stars forced astronomers reformulate definitions of what constituted a planet (Britt 2000). Extrasolar planets may originate as brown dwarf stars, lack light, and are even in some cases as large as Jupiter, yet they orbit stars like planets (Britt 2000). In defining whether these burnt-out brown dwarfs were planets in the early 90s were planets, the issue of Pluto's planetary status again came to the forefront of scientific debate.

The matter is still far from closed. Many scientists today still believe that Pluto is in fact a planet, and support a more expansive definition of what are called planets, rather than the more narrow one advocated by the majority of the scientists at the Prague convention. But although most people cannot remember when Pluto was not a planet, scientifically speaking, in comparison to the other planets, Pluto was discovered relatively recently, in 1930 by Clyde W. Tombaugh at the Lowell Observatory in Flagstaff Arizona (Cain, "Why is Pluto not a planet?" 2008). The discovery had long been anticipated given astronomers had predicted that there would be a 9th planet in the solar system, based upon the behavior of other astral bodies. Tombaugh, while comparing photographic plates of images of a region of the sky, taken two weeks apart noted a moving object in the right orbit of one of the photographs. The object could have been an asteroid, comet -- or a planet. Astronomers speculated and then confirmed that this was the long-sought after 'Planet X,' the 9th planet of the solar system. They even held a contest to 'name that planet' which was won by an eleven-year-old schoolgirl in Oxford, England, who named the new, icy planet after the god of the underworld in Roman mythology (Cain, "Why is Pluto not a planet?" 2008). But today scientists believe that, given the desire to find a 9th planet, these scientists were over-eager in their desire to include Pluto in the list of planets.

It was not until 1978, however, that astronomers began to gain a clearer understanding of Pluto's relative mass and size to other planets. After discovering Pluto's largest Moon, Charon, they estimated the planet's total mass to be approximately 0.0021 Earths, and 2,400 km (1,500 miles) across, roughly half the size of Mercury's 4,880 km (3,032 miles) across. "Pluto is tiny, but it was considered larger than anything else past the orbit of Neptune" at the time (Cain 2008). However, more recent, accurate assessment of Pluto's mass suggested that its size is closer to 2,600 km (1,600 miles) across, far smaller than originally suspected (Cain 2008). In fact, Pluto was found to be half the size of even the smallest of the other eight planets (Britt 2000, p.1). Also, the other moons of Pluto, Nix and Hydra, appear to be part of the general orbital patterns of Charon and Pluto, as if the two larger astral bodies are part of the same gravitational force, rather than the pattern expected of a planet with three moons.

In the ensuing decades, greater knowledge was gained about the far, outer reaches of the solar system that began to put Pluto's status in further doubt. As early 1999, the IAU wrestled with the problem of Pluto by saying it should be classified as both a planet and as a Trans-Neptunian Object, reflecting its distant location (Britt, 2000, p.1). Interestingly, this campaign was dropped, not because of scientific objects, but because of a letter-writing and email campaign protesting the resolution. Still, today, "instead of being the only planet in its region, like the rest of the Solar System, Pluto and its moons are now known to be just a large example of a collection of objects called the Kuiper Belt... Astronomers estimate that there are at least 70,000 icy objects, with the same composition that measure 100 km across or more in the Kuiper Belt. And according to the new rules, Pluto is not a planet. it's just another Kuiper Belt object," a dwarf planet (Cain 2008).

The first serious calls for the demotion of Pluto came with the discovery of Eris, a larger object made of similar icy rock mixture. It also had approximately 25% more mass than Pluto. After Eris' discovery, astronomers decided they would make a final decision about the definition of a planet. If Pluto was a planet, it seemed as if more astral bodies would have to be incorporated into the definition. At the Prague Conference, "the initial proposal, hammered out by a group of seven astronomers, historians and authors, attempted to preserve Pluto as a planet but was widely criticized for diluting the meaning of the word. It would also have made planets out of the asteroid Ceres and Pluto's moon Charon" (Britt 2006).

The conference proved to be one of the most contentious in decades. Eventually, at the conference, scientists came to the first official definition of what constitutes a planet, despite the use of the term in the lay and scientific community for many years. The first parts of the definition that stated a planet was "an object that orbits the sun and is large enough to have become round due to the force of its own gravity" was not controversial (Inman, 2006, p.1.). It was the third addition to the definition that a planet has to dominate the neighborhood around its orbit that was called into question. One astronomer said that this strictness was part of the proposal's intention and praised its rigor: "It's going to be hard to find a new planet...You'd have to find something the size of Mars. Finding a new planet will really mean something" (Inman, 2006, p.2). A planet, in other words, should be something unique and 'special.'

Pluto is a dwarf planet by the... definition and is recognized as the prototype of a new category of trans-Neptunian objects," read the resolution (Britt 2006). Dwarf planets are not considered planets by the IAU. Ceres was classified as a dwarf planet, "the only dwarf planet in the asteroid belt," Charon as a satellite, and given the liberal definition of a dwarf planet, conceivably there could be "hundreds of dwarf planets," in the future (Britt 2008). The majority of scientists were swayed by the stricter definition and the prospect of Pluto's demotion because the other eight planets so clearly dominated all neighboring bodies and Charon, Pluto's extremely large moon was almost half the planet's size and the other two moons appeared to orbit Charon as well as Pluto at times. The other planets of the solar system are far larger than their moons (Britt 2006).

Furthermore, while the other planets more easily sweep up… [END OF PREVIEW] . . . READ MORE

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APA Style

Astrophysical Object Phenomenon.  (2008, August 2).  Retrieved January 16, 2022, from

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"Astrophysical Object Phenomenon."  2 August 2008.  Web.  16 January 2022. <>.

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"Astrophysical Object Phenomenon."  August 2, 2008.  Accessed January 16, 2022.