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How many planets orbit the sun? - Windows to the Universe

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This drawing shows where trans-neptunian objects are found.
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How many planets orbit the sun?

I was wondering if there is a new planet? Are there planets (a tenth planet?) after Pluto belonging to our solar system? What are the names of the new planets discovered in the solar system? Are there any objects that orbit the sun that are not in the same plane as the planets, excluding Pluto, comets, asteroids? Do we know any names to any other planets than those in our solar system? If yes, could you give me any examples?

As of today, January, 26, 2001, it's known that only 9 planets orbit the Sun. There have been many solar system objects that have been discovered recently, but none of them have been classified as planets. And none of them are the mysterious Planet X!

These objects have been called asteroids, minor-planets, trans-neptunian objects, or objects of the Kuiper belt. We'll use the word trans-neptunian object (TNO) because that simply means an object past Neptune. The first TNO to be discovered (beside Pluto!) was discovered in 1992. Since then, over 300 of these objects have been found!

One of the most recent discoveries of a TNO was in October of 2000. Astronomers found a huge TNO and called it 2000 EB 173. It is between 300-700 kilometers in size and as far as non-planets go in the solar system, it is second only in size to asteroid Ceres.

So, although no new planets have been discovered in our solar system, there have been many discoveries of planet systems outside our solar system. One such finding was in April 1999 of three planets around the star Upsilon Andromedae. Many other findings have been made. In fact there was just an announcement last week that astronomers found planets around two other stars. Please see this page for a listing of TNOs.


Submitted by Jana (New Jersey, USA), Sean (Ohio, USA), John (Ohio, USA), Saravanan (India), Puneet (India), Cassie (Colorado, USA), Jason
(January 26, 2001)

Last modified January 26, 2001 by Jennifer Bergman.

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