Planet definition outcome

The IAU have live streaming from the General Assembly about the last draft resolution for the definition of planets. Jocelyn Bell Burnell was chairing the debate (which she does well). It has now finished and the results are finally in although there were votes on having revotes and I think everyone was getting a bit tired. Here are the basic results.



  • Pluto is now a dwarf planet and the traditional eight are just plain planets (the term "classical" was voted down).


  • Ceres is a dwarf planet.


  • 2003 UB313 is probably a dwarf planet.


  • A new class of objects has been created of which the first example is Pluto. These objects lay beyond the orbit of Neptune but are dwarf planets. Presumably this includes 2003 UB313.


  • Charon is just a moon because it is not the "dominant" body in its neighbourhood.
However, Resolution 6b was voted against (as was a recount) so the classification for the objects of which Pluto is the first example has no name. The results is that a committee must now be set up to give it a name.

So we have 8 planets. We have several dwarf planets (Pluto, Ceres, 2003 UB313 and perhaps also 2005 FY9 and 2003 EL61). There is a new class of objects - as yet un-named - which include all the dwarf planets that are beyond Neptune ie. all but Ceres. Is that clear now?

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Posted in astro blog by Stuart on Thursday 24th Aug 2006 (15:29 BST) | 4 Comments | Permalink

Comments: Planet definition outcome

So what is the cut off for determining if a planet is a dwarf or not, and what is the sceintific justification for a planet being a dwarf (instead of a regular planet)?

Posted by Matt on Thursday 24th Aug 2006 (15:52 UTC)

Heh, or I could read the post below this one. Just ignore me.

Posted by Matt on Thursday 24th Aug 2006 (15:56 UTC)

Sorry Matt, I couldn't be bothered to put the whole description again and I was a bit rushed to add a link to the previous post.

I've been editing (a huge job that takes a lot longer than I thought) the IAU session and it is now on the Jodcast if you want to listen to the edited highlights (22 minutes) of what happened.

Posted by Stuart on Thursday 24th Aug 2006 (18:48 UTC)

First let me thank you Stuart, for all the work you have done in covering this issue and the IAU in general. As a lazy beggar who choose sleep over IAU deliberations, the Jodcast was a real pleasure. Me, I was looking forward to tweleve planets, and I'm slighly dissapointed UB won't be (that was the question :-). Now we need new memory jingles.

Posted by Ian Musgrave on Thursday 24th Aug 2006 (22:01 UTC)

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