Planets in Our Solar System
http://www.universetoday.com/13573/why-pluto-is-no-longer-a-planet/ Is pluto a planet?
IS PLUTO A PLANET?
One important part of science is classification. Classification is when scientists decide what categories exist, and they decide what things belong in which categories. This gives the scientists the vocabulary they need in order to talk about science clearly. Why is classification important? Well, imagine you decide to start collecting stamps. At first you might keep your stamps all in a little envelope somewhere, but if your collection grew, you would want a system to help you know what stamps you have. You might put all the cancelled stamps in one place. You might put the stamps with pictures of famous people together, and the stamps with pictures of wildlife together. Scientists order things like this. They do this because it makes what they are studying clear for them, and also so they can talk about things with other scientists. Your stamp collection might be a jumbled mess, but you would still use words like “faces” or “wildlife” if you wanted to tell someone to hand you a specific stamp from your collection.
Until 2006, the classification of “planet” was not very clear. A planet was simply a big thing in space that moved. The word “planet” comes from the Greek word for wanderer, and basically that’s all you had to do to be a planet: wander around in the sky. The definition of planet was very vague. Since we only knew about nine planets, defining them more clearly was not a high priority. Recently, however, stronger telescopes have revealed a lot more things wandering around in the sky. Classifying the planets was becoming important. If you only had nine stamps, you might not organize your stamps at all. But if you suddenly got a bunch of new stamps for your birthday, and you knew you were going to collect even more, you might want to think about organizing your stamps by some system that would make it clear to you. After over two years of debate, nearly three thousand scientists got together to define the word “planet”.The new definition is simple and clear. In order to be a planet, the object must:
1. orbit the sun
2. be large enough that its own gravity makes it spherical in shape
3. clear the neighborhood around its body;
(which means that the object's gravity is strong enough to collect up all the matter around it and its orbit does not overlap with other planets)
Even though the definition seems simple, it clarifies a lot of things for scientists. It also clarifies a lot of things for Pluto in particular. Many scientists had felt that Pluto should not be classified as a planet. It is much smaller than the others; its center of gravity is different; even its orbit is different from the other planets’ orbits, both in shape and in length. These scientists felt that a clearer definition of planet was needed, and that Pluto should be excluded from this definition. Other scientists felt that a broader definition of planets would make it possible to include not only Pluto, but several other recently discovered bodies in the solar system.
Let's return to the stamp collection: imagine that you have eight stamps that are all different sizes, but they all have pictures of wildlife on them. You also have this one little stamp that’s from another country and has a picture of a flag. It’s a stamp, but it’s weird. Then for your birthday you get three more stamps with pictures of flags. Now, do you keep all these new stamps with your regular stamp collection, or do you put them in another envelope to keep them separate? This was basically the kind of decision the scientists had to make. By creating three categories for all celestial bodies, they clarified Pluto’s position as well as the positions of other as-yet-undiscovered wanderers. The new categories created by the scientists are: planets, dwarf planets, and small solar-system bodies. Under the new system, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune are the only real planets. Pluto is separate from the other planets with which it was previously grouped, and is now considered a dwarf planet.
One important part of science is classification. Classification is when scientists decide what categories exist, and they decide what things belong in which categories. This gives the scientists the vocabulary they need in order to talk about science clearly. Why is classification important? Well, imagine you decide to start collecting stamps. At first you might keep your stamps all in a little envelope somewhere, but if your collection grew, you would want a system to help you know what stamps you have. You might put all the cancelled stamps in one place. You might put the stamps with pictures of famous people together, and the stamps with pictures of wildlife together. Scientists order things like this. They do this because it makes what they are studying clear for them, and also so they can talk about things with other scientists. Your stamp collection might be a jumbled mess, but you would still use words like “faces” or “wildlife” if you wanted to tell someone to hand you a specific stamp from your collection.
Until 2006, the classification of “planet” was not very clear. A planet was simply a big thing in space that moved. The word “planet” comes from the Greek word for wanderer, and basically that’s all you had to do to be a planet: wander around in the sky. The definition of planet was very vague. Since we only knew about nine planets, defining them more clearly was not a high priority. Recently, however, stronger telescopes have revealed a lot more things wandering around in the sky. Classifying the planets was becoming important. If you only had nine stamps, you might not organize your stamps at all. But if you suddenly got a bunch of new stamps for your birthday, and you knew you were going to collect even more, you might want to think about organizing your stamps by some system that would make it clear to you. After over two years of debate, nearly three thousand scientists got together to define the word “planet”.The new definition is simple and clear. In order to be a planet, the object must:
1. orbit the sun
2. be large enough that its own gravity makes it spherical in shape
3. clear the neighborhood around its body;
(which means that the object's gravity is strong enough to collect up all the matter around it and its orbit does not overlap with other planets)
Even though the definition seems simple, it clarifies a lot of things for scientists. It also clarifies a lot of things for Pluto in particular. Many scientists had felt that Pluto should not be classified as a planet. It is much smaller than the others; its center of gravity is different; even its orbit is different from the other planets’ orbits, both in shape and in length. These scientists felt that a clearer definition of planet was needed, and that Pluto should be excluded from this definition. Other scientists felt that a broader definition of planets would make it possible to include not only Pluto, but several other recently discovered bodies in the solar system.
Let's return to the stamp collection: imagine that you have eight stamps that are all different sizes, but they all have pictures of wildlife on them. You also have this one little stamp that’s from another country and has a picture of a flag. It’s a stamp, but it’s weird. Then for your birthday you get three more stamps with pictures of flags. Now, do you keep all these new stamps with your regular stamp collection, or do you put them in another envelope to keep them separate? This was basically the kind of decision the scientists had to make. By creating three categories for all celestial bodies, they clarified Pluto’s position as well as the positions of other as-yet-undiscovered wanderers. The new categories created by the scientists are: planets, dwarf planets, and small solar-system bodies. Under the new system, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune are the only real planets. Pluto is separate from the other planets with which it was previously grouped, and is now considered a dwarf planet.