What can you tell me about Planet X, the unknown planet?

Planet X used to be the name for a proposed 10th planet. The "X" stands for the "unknown quantity." Now you may ask, what makes scientists think that there is a 10th planet? The reason is that there is are laws of nature (Kepler and Newton) which balance the motion of the planets with how much mass is in the solar system. So far, even with the discovery of Pluto, these laws suggest that there may be another planet still to be discovered. (By the way, it was by using this law that the planets Neptune and Pluto were discovered in the first place - that is, scientists knew that they should look for more planets because the law could not be balanced).

The Voyagers' results have now yielded more accurate measurements of the masses of the planets. It now looks like that 10th planet can be satisfied by the material which is in the Kuiper Belt, an asteroid belt outside of Neptune and Pluto. So there probably is no planet X.

Submitted by Kayla (age 14, North Dakota, USA)
Submitted by Eric (age 13, California, USA)
Submitted by Dirk (age 44, Wisconsin, USA)
Submitted by Amanda (age 11, New Jersey, USA)
Submitted by Austin (age 8, Texas, USA)
(December 29, 1997)

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Last modified January 29, 2001 by the Windows Team

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