Tenth Planet

A stunning discovery at the far reaches of our solar system raises questions about what makes a planet a planet.

Planet Theory

In this video clip, Michael Brown and astrophysicist Neil deGrasse Tyson disagree on whether the word "planet" has any useful meaning.

Found it!

Michael Brown knew instantly the object he discovered in 2005 was a planet. In this video clip, he explains how. Watch online or subscribe to our video podcast to download the clip.

Ask the Expert

Astronomer Michael Brown of Caltech answers viewer questions about the 10th planet.

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© | Created January 2006