StarChild Question of the Month for December 1998


Is there a Planet X or 10th planet?



There is no known Planet X or 10th planet in our solar system. Scientists have been looking for about a hundred years. It was believed that such a planet was required to explain the orbital characteristics of the outer planets Uranus and Neptune. Many searches have been performed and, to date, no evidence of such a planet has emerged. In addition, better information about the masses of outer planets has also now shown that no other planets are necessary to explain the planetary orbits.

You can get a good historical account of the searches for "Planet X" at:

Read an update on the new objects being found in our solar system which are not being classified as planets!

Yet, there are new planets being discovered!

However, any new planets you may hear, or have heard, about being discovered are around other stars, not our Sun! You can read all about the search for, and discovery of, planets around other stars at

or get a very comprehensive discussion at

How will these new planets be named? The planets that are being found around other stars are given scientific catalog names (like SV168) and not the names of people (real or mythological). All objects, whether moons or asteroids or planets, are named by the International Astronomical Union according to strict guidelines. You can read about this at

Thanks for asking!

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