Pluto to Get Partners? New Definition of "Planet" Proposed

August 16, 2006

Astronomers proposed a new definition of "planet" today.

The proposal would add at least three more planets to the nine we're familiar with, instantly outdating textbooks.

But it could add as many as 50—and that's a problem, some researchers say.

The term "planet" has never had an official definition.

Many scientists have long argued that it was a mistake to call Pluto a planet, since it is much smaller than the other eight generally accepted planets.

Recent discoveries have intensified the debate over Pluto's status and brought the issue to the forefront of the astronomy community.

Now the International Astronomical Union is meeting in Prague, in the Czech Republic, to debate how to best define the term based on physical properties.

Astronomers vote on the proposal next week.

Planets and Plutons

The IAU proposal says that a planet is an object large enough to have become rounded due to the force of its own gravity.

But it's not that simple. What counts as a planet also depends on what it's orbiting around.

A planet has to orbit a star, so rounded objects floating freely through space won't make the cut.

Continued on Next Page >>


SOURCES AND RELATED WEB SITES

ADVERTISEMENT

NATIONAL GEOGRAPHIC'S PHOTO OF THE DAY

NEWS FEEDS     After installing a news reader, click on this icon to download National Geographic News's XML/RSS feed.   After installing a news reader, click on this icon to download National Geographic News's XML/RSS feed.

Get our news delivered directly to your desktop—free.
How to Use XML or RSS

National Geographic Daily News To-Go

Listen to your favorite National Geographic news daily, anytime, anywhere from your mobile phone. No wires or syncing. Download Stitcher free today.
Click here to get 12 months of National Geographic Magazine for $15.