Pluto: A planet or not?
This diagram (left) shows that Pluto, what we thought to be the furthest planet from our Sun was actually closer to it than Neptune in the year 1989 (Circled) when the two planets' orbits intertwined.
Pluto is said to be made of mainly rock and ice. Through a telescope, it has a brownish colour, this is because the thin atmosphere around it is composed of nitrogen, methane and carbon dioxide.
A planet's satellite (moon) often orbits around the planet, Pluto's relation with Charon (its moon) however is considered a "binary system" as both objects are almost as big as each other and rather than Charon orbiting around Pluto, both objects seem to orbit around each other; the centre of their orbits do not lie within either object. For example, our (Earth's) moon's centre of orbit is the Earth, therefore it orbits around that
point/object. Charon's centre of orbit however does not lie within Pluto's point, and neither does Pluto's orbit lie within its moon. They therefore move around a space between them.
This raised another question as to what defines a planet, and whether Pluto should be considered as one; is Pluto's size to insignificant?
As mentioned above, a planet must have enough gravitational pull within itself to be able to hold a sphere/round shape and appearance, it must orbit around A sun, and has cleared it neighbourhood. ("clearing its neighbourhood" I PRESUME means have a clear space around the planet, like the other 8 official planets have, whilst Pluto a "dwarf planet" (see above) is found in the Kuiper Belt and has therefore NOT cleared its neighbourhood). This definition is given by the International Astronomical Union.
So why Pluto should remain a planet?
Pluto being classified as a "dwarf" planet already differentiates it with the rest of the more obvious planets, but still emphasises the fact that this object is nonetheless a planet. The change of Pluto's status therefore is unnecessary as it falls nicely into the category of "dwarf planet".
There is also no official definition for a planet that states anything about where the barycentre of a planet-moon system is. As mentioned above, Charon's centre of orbit does not lie in the centre point of Pluto and that's why they are considered to have a "binary-system". This happens through course of nature and after a few million (billion?) years the same thing may happen to Earth's system. This is not enough of a characteristic to demote Pluto as a planet.
If crossing another planet's orbit is enough to demote a planet, then in that case Neptune should also be eliminated as a planet.
Changing the status of Pluto as the ninth planet will mean changing all the textbooks, posters, syllabi, programmes etc that state otherwise. This will only be a hassle because so far, we have only studied Pluto from the Earth's distance, and we have yet to send a probe to Pluto for further investigation; we are still unsure of what Pluto really is. However a spacecraft will land on Pluto in 2015, then we may be able to study Pluto from a closer view and decide more fairly.
The definitions given for a "planet" is also not detailed enough to be able to judge clearly what makes a planet one and not just a piece of rock/ice in space.
All reasons mentioned above seem to be strong evidence and reason why Pluto should remain a planet, but this question was raised and is being studied for good reasons and argument.
Why should Pluto lose its status as a planet?
Some astronomers and scientists argue that Pluto's size is insignificant; its smaller than the other 7 satellites in the solar system and in proportion to its own moon Charon, it is a small object. In fact, some astronomers consider Pluto and Charon as a double planet in itself rather than a planet-moon relation.
Pluto's orbit is also an unusual one; it's the only orbit that's been found in our solar system that intervenes with another planet's (Neptune's) orbit. Astronomers argue that this may disqualify Pluto as a planet.
As I mentioned above, Pluto is primarily made of rock and ice, just like the 4 inner planets of the Solar System. The outer planets which Pluto is supposedly part of are made of different types of gas, Pluto is not. This misfit suggests that Pluto perhaps is just another piece of rock and ice in space, as it does not follow the pattern (that the further planets from the sun are made of gas and effectively, the further away, must be more gas than rock).
Pluto's status as a planet was not in danger of loss until QB1 was found in 1992. QB1 is an object not much bigger/smaller than an asteroid that orbits around the sun. QB1 is composed of primarily rock and ice, not much different to Pluto and since 1992, over a 100 objects just like QB1 has been found. If Pluto was to be classified as a planet, then so should the other objects such as QB1 which also orbits around the Sun.
Objects such as QB1 that are found beyond Neptune's orbit are known as the Kuiper Belt. Pluto is also found in the Kuiper Belt. Isn't Pluto just merely the largest object found in the said Belt? Isn't it just a particularly large comet/asteroid?
Should Pluto remain a planet? Or should it be reclassified as another Kuiper Belt Object? Or. Should the rest of the Kuiper Belt objects that are relevant in size be classified as planets aswell?
For the sake of open-mindedness, I will acknowledge both sides of this argument as they both have valid points supported by valid theories. However, I think that Pluto should remain as a Planet for the mean time, until 2015 when the first probe sent to Pluto will land. Then we can investigate and study Pluto more from a closer more detailed view and make a more accurate and thorough decision as to what Pluto should be classified as. Changing Pluto's status now before we get a chance to study it further will be pointless and a hassle as textbooks, videos and school curriculum would have to be altered, and that will cause confusion and nothing short of chaos. Why bother, when there is still a possibility that we were right to begin with anyway? To conclude, right now, we should just acknowledge the theories and evidence mentioned above and consider them "possible" rather than "wrong" or "right.
History of Pluto:
Pluto has been defined by scientists and astrologers as a "dwarf planet". A dwarf planet is a "minor planet", an object in the Solar System that holds enough gravity within itself to keep a sphere/round shape. It must also orbit around the Sun and is not a moon of any other dwarf planet/planet in the Solar System. A planet to be classified as one must have "cleared its neighbourhood", whilst a "dwarf planet" must NOT have done this. Hence Pluto is a "dwarf planet".
It was also considered and taught in schools/universities as the furthest planet from our Sun, although this statement had also raised a slight controversy as it doesn't always orbit the furthest; it intertwines with Neptune's orbit, therefore Neptune at times appear to be further away than Pluto.