A planet orbits a star, has enough mass that it's mostly spherical, and is large enough that it's cleared its orbit.
I've received a number of emails and IMs asking me what I think of this definition and what it means for Pluto. My answer is that I love it. No because it demotes Pluto (though that doesn't bother me one bit.) I love it because millions of people all across this jumpin' green sphere are reading about and talking about astronomy and that can only be good.
Posted by: Pharod | August 25, 2006 5:25 AM
pluto is the red-headed step child of the solar system. It's too small, its orbit is eliptical, and most of all, which has hardly been mentioned in this debate over the past couple weeks, its orbit is 17deg out of plane with the rest of the planets!! (mercury being the exception, at 7deg itself) it simply doesn't belong. good riddance, i saw.
Posted by: joe | August 25, 2006 5:42 AM
Pluto is within Neptune's orbit so by this definition, Neptune cannot be a planet as it hasn't cleared its orbit.
I'm glad these people don't write specs for any projects I work on!
Posted by: Steve | August 25, 2006 7:21 AM
I'm sad. Pluto was always my favorite planet. So tiny, so cold, so remote, and a bit mysterious.
Asa makes a great point, though. I don't think I've ever heard this much buzz and public discussion about astronomy!
Posted by: Dawn Foster | August 25, 2006 8:29 AM
So it doesn't matter at all that Pluto has a moon? If Pluto isn't a planet any more, where does that leave Charon? Not that I'm losing sleep over this or anything... I'm just curious.
Posted by: Patrick | August 25, 2006 8:40 AM
Patrick, the latest thinking on Charon is that it's not quite a moon. A moon orbits a planet (more specifically, a point that resides inside a planet) and in the case of the Pluto Charon system, they actually orbit eachother -- that is, they're each orbiting a point that's in space between the two bodies.
There was a proposal on the table to use that feature as a reason to call Pluto and Charon a double planet but that proposal didn't get sufficient support.
- A
Posted by: Asa Dotzler | August 25, 2006 9:09 AM
diffenitions are what everying agrees to, so if someone said pluto was an grape and people agreed to that, it would be true, so therefore everyone considers pluto a grape, i personally don't consider anything a planet that doesn't have life on it.. so if more people agreed to that then earth would be the only planet and others would be just big ass rocks/gas blimps.
Posted by: a | August 25, 2006 11:41 AM
I don't much like that quibbling about barycenters with regard to Charon. I say it's a moon. But nevertheless, having a moon is no particular indication of planet status, since a lot of asteroids that nobody would consider a planet also have moons.
Many people seem to be reacting as if Pluto is somehow being officially removed from the solar system. It's not--the whole point is that there is a lot more to the solar system than eight or nine planets!
Posted by: Matt McIrvin | August 27, 2006 6:36 AM
Once again Pluto doesn't get the respect that it deserves. If it didn't clean out its neighborhood, maybe that's because it has so much more neighborhood to clear out. As if that had something to do with being a planet.
And it doesn't even get credit for having a moon. Why? Because its moon is too big. Go figure.
Posted by: AnotherGuest. | August 28, 2006 6:04 AM
My mind is like a bunch of nothing, but I guess it doesn't bother me. I haven't been up to anything recently. I've pretty much been doing nothing to speak of.
Posted by: Sten77602 | March 12, 2007 10:58 PM
I must say that I feel a bit nostalgic. All my life I liked Pluto. It was very far away, had the coolest orbit and it had some sort of magic. But at least people are agreeing on a planet definition.