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Why Pluto Is Not a Planet? According to the 26 th General Assembly for the International Astronomical Union, Pluto is no longer a planet. More than 2, 500 astronomers, who took part in 7 Symposia, 17 Joint Discussions, and 7 Special Sessions adopted new definition of a planet. From now on, Resolution 5 A defines the planet as a celestial body that: Is in orbit around the Sun; Has enough mass for its self-gravity to overcome the rigid body forces to assume a hydrostatic equilibrium (nearly round) shape, and Has cleared the neighborhood around its orbit (IAU 2006 General Assembly: Result of the IAU Resolution votes.
Press Release) The General Assembly of the IAU made distinction between planets and dwarf planets and agreed that they are two distinct classes of objects (Pluto loses status as a planet, 2006). The dwarf planet, in their opinion, should be considered a celestial body that: Is in orbit around the Sun; Has sufficient mass for its self-gravity to overcome the rigid body forces to assume a hydrostatic equilibrium (nearly round) shape, and Has not cleared the neighborhood around its orbit, and Is not a satellite (IAU 2006 General Assembly: Result of the IAU Resolution votes. Press Release) The first candidates for draw planets became Pluto, Ceres, and 2003 UB 313. In addition, Pluto was recognized as the prototype of a new category of trans-Neptunian objects (IAU 0603: News: IAU 2006 General Assembly: Result of the IAU Resolution votes).
What was the reason of the resolution of the International Astronomical Union? The problem of Pluto has become a subject of heated debates, when the astronomers discovered an object under the temporary name 2003 UB 313. This object was big enough to claim for a status of a planet. The International Astronomical Union faced a dilemma: either to recognize 2003 UB 313 a planet, or to deprive Pluto the status of planet. The object 2003 UB 313 (not a planet) is bigger than Pluto (a planet).
Both of them have significantly smaller mass compared to other planets. In case the astronomers classify the objects of the Solar system with no prejudice, they will inevitably come to a conclusion: four giant planets (Jupiter, Saturn, Uranus and Neptune) fit into their category; four terrestrial planets (Mercury, Venus, Earth and Mars) fit into their category, and all other can be classified under one, or, probably, under several different categories. In such a way, the definition of planet embraces the groups of giant planets and terrestrial planets. At the same time, this definition can hardly be applied to Pluto and to the biggest objects from so-called Kuiper Belt.
We come to conclusion, that inclusion of Pluto in the list of planets significantly decreases the scientific value of the concept of planet. It was desirable that the astronomers come to distinct scientific definition of the planet. What were the most possible solutions for Pluto problem? To deprive Pluto status of a planet (8 planets); This solution implied exclusion of Pluto and 2003 UB 313.
It was one of the most obvious solutions: to acknowledge the fact that in 1930, when Pluto received a status of a planet, a mistake occurred (Britt, 2006). The Solar System consists only of eight planets, thousands of asteroids, and numerous thousands of objects in Kuiper Belt. Pluto is an object of the second magnitude compared to 2003 UB 313. Ceres is the biggest asteroid, correspondingly. Whether such solution can be applicable?
Evidently, it can. The similar procedure was done to Ceres approximately 150 years ago. In 1801 Ceres was discovered and received a status of a planet. Further, in 1802 the next planet was discovered (Place). In 1804 Union followed by Vestas discovery three years later. Finally, the astronomers realized that all those numerous objects cannot be called planets but rather the objects of a new class under the name asteroids.
The only planet that was acknowledged to satisfy new criteria was Neptune. To maintain the status quo (9 planets); What does it mean? Actually, such solution can have undesirable outcomes, as far as it can serve a peculiar sign that all discoveries in the Solar system already occurred and the discovery of a new planet is impossible in principle. To include the newcomer (10 planets); To a certain extent, this solution is quite similar to the second one. In case the astronomers recognize Pluto a planet, they will be forced to recognize all other objects that are bigger than Pluto.
Nowadays, the bigger object is 2003 UB 313. So, Solar System will consist of ten planets (up to a certain moment). As a result, the word planet will lose its meaning and will never be used as a definition. In order to illustrate the thought, we can draw an analogy to the word continent and geological definition continent. The word seems to be an exact scientific term. However, it is not.
The Europe is considered a continent; however, the geologists never discuss scientific meaning of the word. They prefer using more scientifically grounded terms, such as continental crust, continental platforms, but never use simply the term continent. To include all ice objects (53 planets) (It was one of the previous IAU recommendations); This solution is also disputable. Nowadays Iau's recommendation concerns 53 objects equal to planets, however, tomorrow the situation can change. This solution introduces definition of planet on a solid scientific basis. However, it simultaneously includes many other planets into the traditional structure of Solar System.
This definition implies that any celestial body, that is in orbit around the Sun and has sufficient mass for its self-gravity to overcome the rigid body forces to assume a hydrostatic equilibrium (nearly round) shape, should be considered a planet. However, all ten celestial bodies (including Pluto and 2003 UB 313) have such nearly round shape. It means that no celestial body will be excluded from the list. Here we face another problem: how big should the celestial body be to be considered the planet? The biggest asteroid Ceres (which has a nearly round shape) will become the planet for the second time in its history. The previous IAU proposal classified 12 objects as planets (Amir, n.
p. ). However, Kuiper Belt is the area where hundreds (and, probably, thousands) of ice celestial bodies are located. We do not know their exact quantity, as far as we are unable to make exact measurements. In addition, in case we examine ice satellites of giant planets, we can easily notice that almost all such satellites with diameter more than 400 km have a nearly round shape, and all those with diameter less than 200 km, have an irregular shape.
It means, that definition should lie somewhere between those measurements. Nowadays the astronomers know 44 celestial bodies in Kuiper Belt with diameter more than 400 km (including Pluto and 2003 UB 313). It gives us at least 8 + 1 + 44 = 53 planets according to the new definition of a planet. No reaction (How many planets should be, then? ) However, such solution is almost impossible.
In case the members of IAU vote against the resolution, the astronomers will continue facing misunderstandings concerning scientific definition of a planet. Taking into account all assumptions, we can come to conclusion that Iau's resolution was the most logically correct action. In fact, Pluto seems to be unnecessary in some astronomical and physical rules. It doesnt fall under Titles-Bode law and in dependence of the moment of motion and mass.
Pluto's measurements and orbit significantly differs from other planets. In such a way, Pluto hardly will ever achieve the status of a planet in the future, unless the IAU changes its mind. Bibliography Amir, A. A New Solar System. 24 February 2007 < web >.
Britt, R. R. Pluto's Demotion is Well Deserved and Long Overdue. 24 August 2006. 26 February 2007 < web >. IAU 2006 General Assembly: Result of the IAU Resolution votes.
Press Release. 24 August 2006. 26 February 2007 < web >. IAU 0603: News: IAU 2006 General Assembly: Result of the IAU Resolution votes. 24 August 2006. 26 February 2007 < web >. Pluto loses status as a planet. 24 August 2006. 26 February 2007 < web >.
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