So what’s the criteria for define an object in space as a planet ?
from here
From an article:
“a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a … nearly round shape, and has cleared the neighborhood around its orbit.”
But wait… just last week, the news was that they were increasing the number of planets, to twelve. IIRC, the asteroid Ceres and Pluto’s companion Charon were both being added as planets.
Is this a different body of astronomers who are rebelling? Did the same group simply change its mind?
I’m not completely sure about what “has cleared the neighborhood around its orbit” means in practice. If Pluto has not cleared the neighbourhood because of Neptune, then doesn’t that mean that Neptune hasn’t cleared the neighbourhood either? But it would have been really strange to demote Neptune as a planet.
That was the initial proposal, this is the voted on definition.
Yes, and the words “and has cleared the neighborhood around its orbit” were added, which clearly remove Ceres (and other asteroids) and the Pluto-Charon system (and other Kuiper belt objects) from the definition of planets. As far as I can tell, this proposed addition was made public just two days ago, on August 22nd.
I heard that it meant something like “the body contains over 50% of the total mass in its orbit” There’s enough other stuff in or around Pluto’s orbit that it doesn’t have greater than the cutoff percentage. If there was nothing but Pluto in that orbit, then it would be a planet.
Pluto doesn’t go anywhere near Neptune. Its orbit only appears to intersect Neptune’s if you look from a viewpoint perpendicular to the plane of Neptune’s orbit. But in fact Pluto’s orbit is inclined at 17 degrees to Neptune’s, which means Pluto passes far above/below Neptune at the supposed intersection point.
Alive At Both Ends
I believe the objects to which they are referring are Kuiper Belt objects. (Similar to an icy, cold, distant asteroid belt at Pluto’s distance and beyond). Among other objects in the Kuiper belt are Xena and Sedna. (are those names official yet?)
Anyway, I’m not very happy about Pluto’s “demotion” either. :mad:
Sedna is official, Xena is not. And I hope that Xena’s satellite will not be named for a TV show character. You have to have a certain amount of dignity here, you know…
I leave you folks alone for one lousy week and you LOSE A PLANET?
“It’s gone, Jim.”
Decker: My crew is on the ninth planet.
Kirk: There is no ninth planet.
Decker: Don’t you think I know that!
I think this “ups” my SAT scores. I might even get into a collage now.
You have very lofty ideals for yourself! I would simply hope to get into a portrait of any kind… 
My Very Energetic Mother Just Showed Us…
Nothing
(credit goes not to me, but to the lovely and most witty Rhiannon8404)
This planetary debacle might not be over yet. From what I’ve read, only about 5% of the 10,000 or so professional astronomers worldwide actually voted on this issue. (Apparently, there was no provision for electronic voting, so you had to be physically present at the convention to vote.) There are many, many astronomers who don’t like this new definition either, so it’s quite probable that the definition of a planet will be revised, or even completely rewritten, at some time in the future.
You should probably hold off buying any new science books for a few years.
Diceman
I was hoping that these reports of Pluto’s planetary demise might be greatly exaggerated.
This matter isn’t settled yet.
Thanks for the good news.
Huh? If I don’t vote in an election, I don’t have the right to say the result doesn’t count.