Why Isn Pluto a Planet Any More?
You are right about the fact that Pluto’s orbit is quite strange. At some points in its course around the Sun, Pluto overlaps with Neptune, and is even closer than it at points. A fully fledged planet must be the largest object in its orbit, and because Pluto shares with Neptune sometimes, it is demoted for being small. Also, other dwarf planets have been discovered that are the same size or larger than Pluto, and this puts it on shaky ground. Not to mention the fact that Pluto’s position makes the planetary segment of our solar system highly irregular: four small rocks, four gas giants, and one piddly little ball of ice. Courtesy of my science teacher and Bill Bryson’s “A Short History of Nearly Everything”. Make sure to double check, and don’t trust the people with poor grammar!
Originally classified as a planet, Pluto is now considered the largest member of a distinct region called the Kuiper belt. Like other members of the belt, it is composed primarily of rock and ice and is relatively small: approximately a fifth the mass of the Earth’s moon and a third its volume. It has a highly eccentric and highly inclined orbit. The eccentricity takes it from 30 to 49 AU (4.4—7.4 billion km) from the Sun, causing Pluto to occasionally come closer to the Sun than Neptune. Pluto and its largest moon, Charon, are often treated together as a binary system because the barycentre of their orbits does not lie within either body. The International Astronomical Union (IAU) has yet to formalise a definition for binary dwarf planets, and until it passes such a ruling, Charon is classified as a moon of Pluto. Pluto has two known smaller moons, Nix and Hydra, discovered in 2005. From its discovery in 1930 until 2006, Pluto was counted as the Solar System’s ninth planet. In the lat
Here’s the link to the first answer, that was lifted and pasted without attribution: http://en.wikipedia.org/wiki/Pluto Pluto was once called a planet because it was a solid body, thought to be bigger than Mercury, orbiting the sun. Recent decades brought the discovery that it was smaller than Mercury, but it kept its designation as a planet. In the last few years, a number of bodies, some slightly smaller and some larger than Pluto, have been found not much further from the sun, in similar orbits (inclined, and possible coming inside Neptune’s orbit). There is reason to believe that there may be hundreds of them. If Pluto was to be considered a planet, then the new discoveries would have to be also. This would mean that there could be several hundred “planets”. Men with beards but no moustaches decided that this was too untidy, so they changed the DEFINITION of the word “planet” to exclude Pluto and others like it. Thus,
