It's official. There are only 8 planets in our solar system. Pluto has been demoted to the status of "dwarf planet." This was decided by a vote during the congress of the International Astronomical Union on August 24th in Prague.
This is not the first time such a demotion has occured. Ceres, in the asteroid belt was formerly a planet 150 years ago, but was demoted because many other objects in the asteroid belt would have been planets too. Thus the new term "asteroid" was created.
The solar system is made up in neat layers: the first four planets- Mercury, Venus, Earth and Mars are rock planets; then comes the asteroid belt; then comes the four gas giants- Jupiter, Saturn, Uranus and Neptune; lastly comes the Kuiber belt- ice objects that orbit the sun.
The new definition of a planet is: 1) Must be an object that orbits the sun. 2) Must have enough gravity of its own to make itself spherical. 3) Must have significantly cleared other objects from its path. 4) Must not orbit another sattelite of the Sun.
Ceres is not a planet because it has many asteroids in close vicinity. Ceres has been elevated to the status of "dwarf planet." Xena, Pluto and Charon (a satellite of Pluto) are not planets, due to their location in the Kuiber belt, in close vicinity to thousands of ice satellites.
Throw this trivia question at some one to stump them! How many planets does our solar system have? 9. Wrong- it's now 8.
2 comments:
The term "pluton" was very nearly used. There must have been a number of astronomers who felt that it would be too great a disappointment if Pluto was called a pluton. That must be why the term "dwarf planet" was arrived at. The International Astronomical Union was very clear in saying that Pluto is no longer in the same category as the other planets. I feel that "dwarf planet" confuses the issue and that pluton would have been a better name.
As long as it still knows who it is. Like all the mao's in China wondering wht their not cats.
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