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

Planet X used to be the name for a suggested 10th planet. The "X" means "unknown." Now you may ask, what makes scientists think that there is a 10th planet? Scientists can tell by the motion of the planets where other planets might be. So far, even with the discovery of Pluto, this motion suggests that there may be another planet still to be discovered. (By the way, it was this way that the planets Neptune and Pluto were discovered in the first place.)

However,it now looks like that the idea of the 10th planet can be satisfied by 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)

---

Last modified January 29, 2001 by the Windows Team

The source of this material is Windows to the Universe, at http://www.windows.ucar.edu/ at the University Corporation for Atmospheric Research (UCAR). © The Regents of the University of Michigan. Windows to the Universe® is a registered trademark of UCAR. All Rights Reserved. Site policies and disclaimer