And then there were 12

[mdlbear]

The committee of the IAU that was studying Pluto's status has finally announced its new definition of "planet" (it will be voted on next week). It's simple, straightforward, sensible, hard to argue with -- and it would mean that the Solar System will have 12 known planets.

According to the IAU's press release (thanks to this article in Scientific American's newsblog for the link) the definition reads:

A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet.

There is also a new category of "plutons" -- small planets that orbit with periods of more than 200 years. There are three of them so far, with more expected.

So here's the list you've all been waiting for:

1. Mercury
2. Venus
3. Earth -- the moon is small enough to be considered a satellite
4. Mars
5. Ceres
6. Jupiter
7. Saturn
8. Uranus
9. Neptune
10. Pluto and Charon (tied for 10th place)
11.  
12. 2003 UB313 (Xena)

Comments

And that's just for now

[capplor.livejournal.com]

The article I read mentioned 43 other known "objects" that may qualify as planets when they get more data.

Sounds like the old joke about memorizing the names of the US presidents -- "Yea, Dad, but when YOU were a kid there were a lot fewer".