In order to determine whether or not Pluto is a planet, a number of issues must be raised and analysed. This essay will look at the set of criteria an object must satisfy in order to be classified as a planet. They are: The object must be in orbit around the sun, The object must be massive enough to be a sphere by its own gravitational force, and it must have cleared the neighbourhood around its orbit.
It can be argued that Pluto satisfies the first rule of classifying an object as a planet, since it is in orbit around the sun. This can be seen from official photographs and texts on the solar system, which clearly show Pluto with its own circular orbit around the sun:
Figure 1.0: http://img684.imageshack.us/i/solarsystem.gif/
It can be seen from Figure 1.0 that Pluto has its own unique orbit around the sun, fulfilling the first of this set of criteria. However, it may be argued that Pluto’s orbit is questionable, since it regularly interferes with the running order of the planets. For example, Pluto's orbit appears to intersect Neptune's, and for a period of about 20 years Pluto is slightly closer to the sun than Neptune [1] . Therefore, it can be argued that Pluto’s status as a planet is questionable, since it does not maintain a fixed orbit around the sun. On the other hand, it may be argued that while this orbit is eccentric, it still fulfills one of the set of criteria by being in orbit around the sun. Therefore, it can be argued that Pluto can be classified as a planet under the criteria set by the International Astronomical Union (IAU).
In addition to its orbit, Pluto may be referred to as a planet, since it also fulfills the second rule by which an object is judged to be a planet – that it must be massive enough to be a sphere by its own gravitational force. It can be argued that it does possess gravitational qualities. It does possess a gravitational pull of 0.637, compared to 1 for Earth [2]. Although it may be argued that this is an almost negligible force, it is nonetheless a gravitational pull belonging to Pluto. However, it may be argued that its miniscule gravitational pull allows it to be influenced by other planets. Malhorta supports this when he points out that Pluto’s gravitational force tends to be provided by Neptune, when Neptune’s gravitational force pulls Pluto into its own orbit [3]. Although, this is a temporary phenomenon. On the other hand, it can be argued that Pluto still satisfies the second law of the IAU planet classification by possessing its own gravitational force. Therefore, it may be argued that by these standards, Pluto is indeed a planet.
In addition to gravitational force, an object must also satisfy the third criterion in order to be classified as a planet. This is: it must clear the neighbourhood around its orbit. This means that it must become gravitationally dominant within its own orbit and be influenced by its surrounding objects. It can be argued that Pluto does indeed satisfy this criterion, when it is seen that Pluto has three moons: Charon, Nix, and Hydra [4], which are all influenced by Pluto’s gravitational force. This can be illustrated by the following:
It can be seen from Figure 2.0 that all three of Pluto’s moons are closely within orbit of their influential planet. However, it may be argued once again that Pluto does not strictly adhere to this criterion, since its orbit is occasionally intercepted by that of Neptune, which has a greater gravitational pull, and brings Pluto into its own orbit [5]. Again this is a temporary phenomenon. It can be argued that while Pluto is only influenced by Neptune’s orbit once every twenty years [6], Pluto is still unable to be gravitationally dominant, and this does not satisfy the criterion of clearing the neighbourhood around its orbit. Overall , it may be argued that Pluto is not a planet, since it does not satisfy this IAU criterion for classifying a planet.
In conclusion, it may be argued that while Pluto satisfies two of the three criterion for planetary classification, it still fails to meet the standards of the third and final criterion. Pluto orbits the sun, meaning that it fits the classification of a planet. In addition, it is a sphere by its own gravitational force, possessing three moons in its orbit. Therefore, Pluto could be classified as a planet for this reason. However, Pluto fails to clear the neighbourhood of its orbit, by intercepting Neptune and coming under the influence of Neptune’s gravitational pull, meaning that it fails to be gravitationally dominant. For this reason, Pluto fails to meet the criteria necessary to be classified as a planet. Therefore, Pluto is not a classified planet.
Bibliography
Malhorta, Renu, Dynamics of Pluto, http://nineplanets.org/plutodyn.html, (accessed on 16th February, 2011), 1997.
Perez, Daniel, http://library.thinkquest.org/, Pluto: The Far Planet, (accessed on 16th February, 2011), 2005.
Schilling, Govert, Pluto’s Twins Get Their Name, http://news.sciencemag.org/, (accessed on 16th February, 2011), 2006.
[1] Renu Malhorta, Dynamics of Pluto, http://nineplanets.org/plutodyn.html, (accessed on 16th February, 2011), 1997.
[2] Daniel Perez, http://library.thinkquest.org, Pluto: The Far Planet, (accessed on 16th February, 2011), 2005.
[3] Malhorta, 1997.
[4] Govert Schilling, Pluto’s Twins Get Their Name, http://news.sciencemag.org, (accessed on 16th February, 2011), 2006.
[5] Malhorta, 1997.
[6] Malhorta, 1997.
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