And then there were 12

[groovychk]

http://www.khaleejtimes.com/DisplayArticleNew.asp?xfile=data/theworld/2006/August/theworld_August550.xml§ion=theworld

So now the IAU says we have 12 Planets!



Mercury
Venus
Earth
Mars
Ceres
Jupiter
Uranus
Neptune
Pluto & Charon
Xena

My very educated mother can't just use nine planets considering xena. (heh - weak - but the best I can do on short notice)

So the conclusion is that any star orbiting object (and not orbiting another planet) with gravity strong enough to pull itself into a sphere is a planet. Charon was formerly considered a moon of Pluto (along with Hydra and Nix) but is now considered a planet on its own making Pluto-Charon a double planet.

The Pluto type objects are being given a new classification of "Plutons"

... the IAU said Pluto meets its proposed new definition of a planet: any round object larger than 800 kilometers (nearly 500 miles) in diameter that orbits the sun and has a mass roughly one-12,000th that of Earth. Moons and asteroids will make the grade if they meet those basic tests.

Roundness is key, experts said, because it indicates an object has enough self-gravity to pull itself into a spherical shape. Yet Earth’s moon would not qualify because the two bodies’ common center of gravity lies below the surface of the Earth.

Of course this would also seem to mean Sedna and Quaoar will be planets as well. Also true for Orcus (90482 Orcus), Ixion (28978 Ixion), Varuna (20000 Varuna), "Easterbunny" (2005 FY₉) and "Santa" (2003 EL₆₁).

I'm glad to see Ceres in there - I always wanted it to be a planet. Click HERE for a great graphic of all the other objects being considered for planet status.

Comments

No Sir, I don't like it. I don't like it at all.

[(Anonymous)]

I think this definition is still too nebulous, and the size of 800km is too small. By my count there would be at least 4 more objects (55637) 2002 UX25,(55636) 2002 TX300,(19308) 1996 TO66, and (84522) 2002 TC302. And with current theories there could be hundreds of kuiper objects that fit the bill.
Personally to be called a planet I would go by this criteria. Granted I am just pulling these numbers out of my ass, but a degree in physics says I can do this with a bit of authority and reasoning.

The object must orbit the sun and not another planet. In the case of a double planet the gravitational centre of mass must be outside either planets surface.
As well the object must meet 2 of the following criteria.
-the size should be more on the order of >2000km.
-the orbital eccentricity should be roundish, say <0.1
-the object should have an atmosphere.

In this way we know the objects will be large enough for gravity to pull them into a sphere. And it will take into account oddball planets that may have been swung into bizarre orbits and inclinations by passing stars or collisions. However it would not include large trans kuiper objects that would be a planet under the new rules, and of which there could be hundreds of.

But hey, that's just me. what do I know.
-Zaphod

Re: No Sir, I don't like it. I don't like it at all.

[groovychk.livejournal.com]

Well pooh :-P
This way we're more like the system from Firefly. Hehe.
So any kind of atmosphere? Many of those worlds in the kuiper/oort will have them because of the deep cold. Pluto does - not sure about Charon - it might well. Ceres might have some very minor atmosphere. Mercury does.
I like the idea of a whole nother solar system in the outer belts. :-) And I always wanted poor Ceres to be a planet. It initially was but it got yanked.